Corrosion effects in deposit environments , together with the glaze adherence and fit, could cause severe deterioration accompanied by different types of defects or growth of corrosion products. The aim of this work was to identify the source of surface degradation of the lead-glazed ceramics sets from the Prague area from the Romanesque to the Renaissance period. A combination of X-ray fluorescence (XRF), X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), and simultaneous thermal analysis (STA) techniques along with stress state calculations was used to study the defects. Based on the interpretation of the possible sources of the observed defects, four types of degradation effects were schematically expressed for the archaeological samples. It was shown that the glazes were already appropriately chosen during the production of the Romanesque tiles and that their degradation occurred only due to long-term exposure to unsuitable environmental conditions. The majority of historical glazed objects, whether they are utility goods, technical ceramics, stoves, or ceramic tiles, were provided with lead glazes with various colouring additives ,3,4,5,6.Study of defects created by the interaction of the glaze with the shard;Study of surface defects of glazes caused by the effect of the surrounding environment on the glaze layer itself.The defectoscopy (defect control) of glazes can be divided into two areas:Both areas can simultaneously contribute to the formation and growth of defects, i.e., the mismatch between the stress states of the glaze and the shards, as well as the action of corrosion factors. The first step in identifying the sources of defects is the evaluation of the consistency of the glaze and the shard material, followed by the evaluation of the degradation processes associated with the identification of the corrosion products. The chemical stability of the glaze layer can be influenced by three types of factors, namely the surrounding environment , the physical conditions of the degradation  ratio or area/volume, etc.) and the condition of the material that is subject to degradation  ,16. Contg), the set points (Tn), and other characteristic temperatures, i.e., the softening point (Td), could be used to evaluate the stage of the stress (σ) developed within the glaze and its substrate in MPa. The results of the graphical comparison of the measured curves, which are shifted to the set point of the glaze, and the results of the differences in the coefficients of linear thermal expansion can be compared with the calculations of the stress relations [g, onset crystallisation temperature Tx crystallisation temperature Tc and melting temperature Tm [The experimental determination of the stress relations and behaviour of glazed ceramic materials has an essential importance for evaluating the development of defects and deformations induced by the state of the stress established in the glaze-ceramic substrate system. The theoretical determination of flexion behaviour and stress state of glazed ceramic materials has considerable limits. The commonly used experimental methods to evaluate the stress or glaze to ceramic body adhesion are mainly the Steger method, glazed ring method, or different types of thermal analyses, i.e., optical dilatometry, dilatometry, or thermomechanical analyses ,36,37,38elations ,43,44,45ature Tm ,47,48.The aim of the presented work is the defectoscopy of lead glazes of archaeological finds with the determination of the source of their damage. The collection of glazed ceramic objects and fragments was selected to capture various types of Prague finds from the late Romanesque period (11th century) to the High Renaissance (18th century) ,50. All For the study of the degradation processes of glazes, fragments of archaeological finds of various types and dates, from the Romanesque period to the Gothic period to the Renaissance, were selected. The evaluated set contained more than 850 fragments, and 24 glazed samples were used to investigate the identification of the origin and cause of the defects : four frα radiation over the angular range of 5–80° 2θ. The measured data were evaluated using the PANalytical High Score Plus 4.0 software package . The semi-quantitative analysis of the ceramic bodies and glazes was performed using the Reference Intensity Ratio (RIR) values from the PDF4+ database.The initial characterisation of the chemical and mineralogical composition of the glazes and ceramic bodies of the studied set was performed using X-ray techniques. The chemical compositions of the ceramic bodies in the form of powdered samples and glazes in the form of flat samples were determined by X-ray fluorescence analysis (XRF). A fully automatic sequential WD-XRF Performix spectrometer  equipped with an Rd anode X-ray tube was used for the analysis. The acquired data were evaluated using Oxsas standardless software , and the measured data were further evaluated based on the measurement error. The chemical composition of the ceramic bodies and glazes was summarised by a principal component analysis (PCA) using XLStat statistical software for MS Excel. This statistical classification divided the obtained data according to quantitative variables, i.e., the identified oxides. The PCA method is used as a statistical evaluation of data obtained from XRF analyses for large sets of shards or input raw materials for their illustrative and effective differentiation ,52,53. TThe thermal analyses, especially the dilatometric measurements (DIL), thermomechanical analysis (TMA), and simultaneous Thermogravimetry/Differential Thermal Analysis (TG-DTA), were used to evaluate the glaze characteristic temperatures, glaze fit, and glaze adherence. Due to the limited amount of glaze samples of some of the studied archaeological fragments, the sample properties were calculated as a function of the composition using the Priven-2000 empirical model of SciGlass software and the glass property database ,55. The −1 or 5 °C·min−1 in a temperature range from room temperature (RT) to 800, 900, 1000, or 1200 °C. A controlled helium flow rate of 20 mL min−1, to ensure an inert atmosphere during the measurement, was used. The gas release (mainly H2O and CO2) was measured through a silica capillary with a ThermoStarTM GSD320 quadrupole-type mass spectrometer  in the range of 300 AMU. The Linseis Acquisition software controlled the measurement, and the detection of released gases was performed using the Quadera 4.62 software. The measured data were evaluated in the Linseis TA Evaluation software. The dilatometric measurements of ceramic bodies and glazes were carried out using a LINSEIS L75 HS 1600C PT  dilatometer. The ceramic bodies were analysed in the form of compact rectangular prism samples (dimensions of approx. 20 × 5 × 5 mm), and the glazes were analysed in the form of cylindrical samples (size of approx. 20 × 5 mm), which were cut from the fired compact samples. The measurements were carried out at heating rate of 5 °C min−1 and with a zero adjustment at the controlled force of 300 mN in a helium flow. The temperature range was 25–700 °C for the ceramic body samples and 25 °C for the deformation temperature of the glaze samples. The measuring process of the ceramic body samples consisted of several stages. First, annealing at a selected temperature mode was performed with dried compact samples. The strain-temperature dependence from the first annealing is influenced by thermal expansion and also by contraction due to the dehydroxylation (elimination of hydroxyl groups). The second measurement of the sample was performed on the previously analysed compact sample, and the degree of rehydroxylation of the sample was zero. The difference between these two annealing steps is the degree of natural irreversible moisture expansion of the rehydroxylation of the annealed sample. The second annealing dependence, therefore, corresponds to the thermal expansion of the studied ceramic body. The third and fourth measurements were performed only for selected compact ceramic body samples that were subjected to hydrothermal treatment in the autoclave  [For the simultaneous thermal analysis ) in the TG-DTA mode, the LINSEIS STA Platinum Series 1600/1750 °C HiRes system for 50 ± 0.05 mg of a powdered sample was used. The measurement was carried out in a platinum crucible with a lid at the heating rate of 10 °C minPa, 5 h) ,57,58. TSurface conditions, types of defects, and the presence of corrosion layers or products were examined using microscopic observations. An Olympus BX51 polarising optical microscope  with or without crossed polarisers and a Canon 500D digital SLR camera were used to investigate thin sections of the selected archaeological samples. An Olympus SZ61 stereomicroscope  with a ProgRes CT3 digital camera was mainly used to study the surface conditions and defects of the individual fragments. The images were processed in NIS Elements AR 4.60 and ZoomBrowser EX software. The obtained data were supplemented by evaluating the homogeneity, corrosion layers, pigments, and glaze morphology of the crystalline phases using a Tescan VEGA 3 LMU electron microscope  equipped with a chemical microanalysis using an OXFORD Instruments INCA 350 Energy-dispersive X-ray spectroscopy (EDS) analyser.The initial characterisation of the chemical composition of shards and glazes was performed using the XRF method, and the measurement results were statistically evaluated using principal component analysis. 2O3 and minor components of MnO were recorded in the fragmentary materials of the tiles. From the point of view of comparing the differences according to the different use of individual shard materials, the shard materials of the technical ceramics are closest to the stove tiles.The results show that the variability in the composition of the shards is primarily determined by the typology of the ceramic product. The sets of the oldest finds of Romanesque and Gothic tiles (brown circle) show the greatest variation in the chemical composition of the shard materials; the composition is more variable in the younger group of finds. The statistical evaluation shows that the shards are similar and differ primarily in the mutual ratio of silicon dioxide and aluminium, where the ratio is the highest in the oldest shards. A higher content of titanium dioxide was recorded in the younger finds, and a higher proportion of mainly Fe2 or other minor components, e.g., ZnO. In terms of the phase composition, the amorphous phase significantly prevailed in all of them; the crystalline components mainly contained lead feldspars with variable composition , colouring admixtures, potash, or corrosion products. The highest proportion of Fe2O3, similar to that of the shards, was found in the glazes of the Romanesque and Gothic tiles, R1–4 and G1–3, respectively. In the Gothic tiles G1, the colouring component in the form of crystalline hematite was confirmed (XRD), and individual clusters of crystals were observed by light microscopy (2O4) in the R4 tile, Fe-mineral with Pb admixture in the R1 and G3 tiles, another admixture could be fayalite (Fe2SiO4). For all the tiles, the corrosion products in the form of hydrated ferric and lead phosphates and lead feldspar formed by firing were identified (XRD).The chemical composition of glazes is correlated in croscopy . Various2O3, which can act in low-melting glazes like a slurp. All the green glazes of tiles S8 and S9 and the large-format wall reliefs W1 and W2 contained colouring components with a combination of Cu (0.2–4 wt.%) and Fe (0.3–1 wt.%) oxides. This combination of ionic dyes was also the main colouring admixture of other Renaissance green glazes on the technical ceramics T1, T2, and T3 and the youngest bowl find presented. They were combined with the melting admixture ZnO, which positively affects the resulting gloss of the glaze, and the opacifier SnO2 was confirmed in the form of cassiterite (XRD). Cassiterite was also identified as the main crystalline phase in the glazes of the faience imports F1 and F2, whose white and blue glazes contained 3.4–11 wt.% SnO2.The majority of the brown-coloured glazes , and Cl (0.4–1.4 wt.%) was recorded for most of the glazed finds from the pit environment. Mainly quartz, K-feldspar, and Ca-albite were identified in the fragmentary materials, which came from the colouring components hematite (tile), anatase, or rutile. Furthermore, a higher proportion of CaO was identified in the shards as anorthite or gehlenite, or diopside . In addition to the main minerals, mullite was also identified in the basin (M1).In the white and blue glazes of samples F1 , and in The individual groups were evaluated, which were sorted by age and defects. First, a set of Romanesque tiles was presented, then tiles from Gothic mosaic paving and modern utility goods (pan) were studied, followed by the most numerous set of Renaissance tiles; the last group consists of representatives, faience imports, and technical ceramics and relief large-format tiles.In the first set of Romanesque glazed tiles, numerous cracks and surface corrosion crusts were identified during the initial survey. To determine possible sources of the damage, calculations of the stress states of the glaze-ceramic shard systems were performed. The values of the longitudinal expansion of the shards were obtained dilatometrically, the values of the R1 and R4 glazes were measured with a thermomechanical analyser and compared with the calculations by the SciGlass software, and for the R2 and R3 glazes, the data calculated by the software were used to calculate the stress states. Corrosion products contain mainly phosphorus, lead, and calcium in the form of hydrated lead-calcium phosphates, e.g., wicksite, or carbonates, mainly cerussite. Furthermore, various degrees of surface damage were confirmed by the microscopic observations a–c.3. P, Ca, and Pb  were identified in the area of the crust edges. The corrosion crusts grew through the glaze until they came into contact with the substrate, and their expansion caused the glaze to peel off. When cracks from the centre of the corrosion crusts developed, a local change in the stress and a violation of the strength limit of the glazes in the place of the crusts took place. Even though the paving was made with the glaze in a moderate compressive prestress , it significantly degraded when placed in the ground. In the relief-decorated tiles (mainly R1 and R4), the plastic decor was damaged by surface mechanical abrasion, visible in The course of the stress states of the samples of the Romanesque tiles calculated from the second dilatation measurements of the fragments characterise the state of the samples after firing d,e. It wThe defectoscopy of the glaze of the younger Gothic group of the archaeological paving G1 was evaluated using optical analyses. On the surface of the Gothic tile samples, only the partially preserved remains of the glaze were strongly cracked. A tiny interlayer between the glaze and the porous sherd mass was identified as peeling, see In the case of the fragments of the M1 pan, a network of fine cracks was observed a,c; on s2O5) and sulphur (7 wt.% SO3) was identified by the XRF analysis. Sulphates were also determined in the clays of the individual layers of the pit in the form of leachates in values of up to 5563 mgkg−1, which caused the activation of corrosion and the formation of defects. From the longitudinal expansion data calculated by the software and measured by the thermomechanical analyser in Based on the measured values from the dilatometer and the thermomechanical analyser, tensile stress leading to cracking of the glazes was detected in the tile glazes. The measured relative expansions were compared with each other and then used to calculate the stress states d and ver2+ ions is visible.The two three-component systems (shard-glaze-underglaze decor) of the imported faience, which have a different chemical and mineralogical composition due to the higher content of calcium and magnesium components compared to the other studied samples, were also included in the selection on the study of the degradation processes and differed from each other in the content of the individual types of calcium minerals. The last group of studied samples of archaeological glazed ceramics is a set of technical ceramics and two large-format relief-decorated lunette tiles, in which microscopic observations showed similar manifestations of the degradation effect of green glazes a,c, whicTo identify the stress states of the studied glaze-shard mass systems, calculations of the stress states and values of their total difference  were used, which were compared with a graphical evaluation of the measured expansion or thermomechanical curves. A summary of the measured data and calculated stress states, together with the most frequent defects and identified corrosion products, is presented in Another manifestation of the degradation of the glazed ceramics can be the gradual crazing (delayed crazing)—The last type of degradation process, captured in Archaeological glazed ceramic finds with porous shards show a number of defects. The aim of studying their surfaces was to describe the damage and determine the source of the damage. From the results of the defectoscopy of the glazes of a selected set of archaeological finds, four types of degradation of the glazed ceramics were traced. The knowledge gained is useful for both contemporary and historical glazed ceramics and applicable to a wide range of samples. The scheme in


Estimation of children’s chronological age is highly important in human and forensic sciences. The Demirjian method has been reported as accurate for this purpose. The literature review shows some evidence that the accuracy of estimating chronological age via the Demirjian standards is not a straightforward process. The objective of this research is to analyze the reliability of the Demirjian standards in Portuguese and Spanish children and adolescents and adapt it to include sex and group age as contingent factors. Methods: Orthopantomographs of 574 Portuguese and Spanish male and female children and adolescents were employed to test the reliability of the Demirjian method. After testing for inter-rater consistency and age estimation using the Demirjian standards, multiple regression analysis was performed controlling for sex and age group. Results: The Demirjian standards overestimated chronological age for both sexes, mainly for females. Through the development of regression functions, more detailed dental age estimation was performed. The predictive capacities of the Demirjian method and the significant teeth varied as a function of children’s age. The Demirjian global standard predicted over 65% of the variance of the chronological age. Taking a tooth-by-tooth approach, the predictive ability increased by over 70%. Conclusions: The accuracy of estimating chronological age via the Demirjian method is not as reliable as it might appear, judging from the results found according to age group and according to sex crossed with age group. Age estimation plays a prominent role in forensic sciences, anthropology, human sciences, medical jurisprudence, pediatrics, and orthodontics, and “(…) is one of the most important characteristics used to establish the identity of any individual in different legal, forensic, or anthropological research context” , p. 203.The identification of victims is essential not only for humanitarian reasons, but also because it is needed for civil and/or criminal investigations, being used in many different situations such as immigration, child abuse, and criminal examination ,4,5,6,7.Teething provides valuable information for the identification process through age estimation ,13,14,15Visualization of dental radiographs in clinical dental practice provides useful information for the most varied types of diagnosis and treatment plans. Through these radiographic records, in children and young adults, we can assess the development of dental maturity as they present morphologically different stages of formation and mineralization . This isDental age can be determined by dental eruption and mineralization, the former being an event of short duration, related to the number of teeth emerging in the buccal cavity, during mixed dentition . BesidesSeveral methods have been proposed for estimating chronological age by means of dental maturity and mineralization, among which the Demirjian et al.  method iAccording to Demirjian et al. , to use The literature review tends to show that estimating chronological age by means of the dental mineralization stage is not a straightforward analysis as some contingent factors may influence the relationship, namely age group, sex, and the tooth under analysis. Several researchers found that the Demirjian standards need re-specification in order to correct for the over-estimation  and Spanish (n = 304) Caucasian children aged between 6 and 14 years, 296 boys  and 278 girls . The sample calculation was performed using the sample size determination formula based on the estimated proportion of the population with p  and q  unknown [The collected sample represents central and northern Portugal and Spain . The sample comprises 574 dental radiographs from Portuguese . Informed consent was requested from the children’s parents/guardians.Inclusion criteria: Children and adolescents aged 6 to 14 years. The following radiological criteria of exclusion were applied: lack of clarity of dental structures due to problems of contrast, movement, or artifacts; impacted teeth; radiopaque obturations or crowns; periapical lesions; endodontic treatment teeth; crowns bridging neighboring teeth.To replicate Demirjian’s original procedure, we focused on 7 teeth from the left lower quadrant  to assess a subject’s dental maturity.Data analyses were performed for each tooth and targeted age group and sex sub-samples using the Statistical Package for Social Sciences (IBM SPSS).The radiographs were evaluated by two different examiners, both with experience in dental radiology. In order to test for inter-rater reliability, we used the intra-class correlation coefficient (ICC1) by Shrout and Fleiss . AdditioSubjectivity plays an important role in categorizing dental maturity with the Demirjian standards. Some authors studied the accuracy assessment of dental age estimation with the Willems, Demirjian and Nolla methods in Spanish children . TherefoSimple and multiple linear regressions were used to obtain a parsimonious model, allowing estimation of chronological age from the measurements made of the seven teeth based on each method and the variables of sex and age group, since in previous studies the Demirjian method is shown to be sensitive to these variables ,36,37,38The inter-rater agreement test of 72 individuals by means of the Intra-class Correlation Coefficient (ICC1), returned values indicating that subjectivity in codifying dental maturity is not a matter of concern in this study. ICC1 values found for each tooth ranged from 0.77 to 0.86 for single rater and 0.93 to 0.98 for the average of raters. ICC1 for Demirjian score (seven teeth) is even better with 0.92 for single rater and 0.98 for the average of raters thus showing clear convergence on decisions made.p < 0.05), thus showing good consistency over time. Subjectivity should therefore be ruled out as a possible bias in later results, as shown in Test-retest of ratings (6-month time lag) returned values ranging from 0.78 to 0.95 . However, when we use the seven teeth, the proportion of age estimation is very similar in boys and girls . The equations forecasting chronological age for boys and girls from the Demirjian global score and for significant teeth are shown at the end of A comparison of children’s real chronological age and estimated age indicated, for both boys and girls, an overestimation when applying the Demirjian method. That overestimation is found in girls in all age groups, with higher values from 6 to 7 years and from 11 to 13 (see error column for girls in p < 0.05. The youngest age groups (up to 9 years of age) are predicted most significantly. More specifically, the most strongly predicted age groups were identified in boys from 7 to 8 years of age  and from 8 to 9 years (R2 = 73.1%), and in girls from 6 to 7 years (R2 = 68.3%) and from 8 to 9 years (R2 = 64.1%). The age group least predicted by the method was from 10 to 11 years, for both boys (R2 = 20.7%) and girls (R2 = 21.3%).2 coefficient lets us compare the magnitude of the predictive capacities of each tooth. The most significant teeth are found to be the canine, second molar, and second pre-molar. The tooth with the least predictive capacity is the central incisor. A comparison of tooth-by-tooth estimation between boys and girls shows that the central incisor, lateral incisor, second pre-molar, and second molar have the greater predictive capacity in boys. In turn, the canine, first pre-molar, and first molar have the greater predictive capacity in girls.Finally, the regression equations of each tooth in boys and girls are presented see . The R2 Estimation of children’s chronological age is important for several reasons and the Demirjian standards have been reported as accurate for this purpose. The Demirjian global score was able to predict 65.1% of the variance of the chronological age of Portuguese and Spanish children and using the seven teeth increases the predictive abilities to 71.7%. The Demirjian standards overestimated chronological age for both sexes, mainly for females. The predictive capacities of the Demirjian method and the significant teeth varied as a function of children’s age. Despite these results, there is an indication that the Demirjian scores are of limited use  report aOccasional reports of re-specification of the Demirjian standards in order to account for ethnic or age differences led us to hypothesize that there are contingency factors  that may require further investigation.R2 = 76.9%) and from 8 to 9 years (2R = 73.1%), while for girls it was 6 to 7 years old (R2 = 68.3%) and from 8 to 9 years (2R = 64.1%). The age group least predicted by the method was from 10 to 11 years, in both boys (R2 = 20.7%) and girls (R2 = 21.3%). Indeed, the literature shows that accuracy decreases with age even when using deciduous teeth for estimation [The influential study of Demirjian et al.  has sometimation . Koshy atimation  also fouOur results gave support to the two hypotheses formulated: H1: the estimation of chronological age by means of Demirjian scores varies across age groups both for global score and tooth score per se; and H2: The accuracy of estimation of chronological age by means of the Demirjian scores varies with sex, both for global score and tooth score per se.Comparison between children’s real chronological age and estimated age indicated overestimation of chronological age for both boys (overestimation of 10.22 months) and girls (overestimation of 15.13 months). The application of the London atlas of tooth development and eruption showed an average overestimation of age by only one month in the Portuguese population, although further studies are needed . ApplyinRevisiting the study by Cruz-Ladeira et al. , which aIn summary, our results are in line with studies indicating the existence of inaccuracies in estimating chronological age using the Demirjian method. For estimation with each tooth taken individually, the results lead us to conclude that the most significant teeth are the canine, the second molar, and the second pre-molar, with the central incisor being the tooth with the least predictive capacity. A comparison of tooth-by-tooth estimation between boys and girls reveals that the greatest predictive capacities lie in different teeth for boys and girls. As limitations of this research, the lack of proper validation methodology  should be noted, resulting in caution in the interpretation of results. The scope for generalizing the results becomes restricted since the sample did not cover all of the Iberian Peninsula. A larger sample, stratified according to age and sex, would allow a broader range of results, improving the external validity of the results.The accuracy of estimating chronological age via the Demirjian standards is not as straightforward as it might appear, judging from the results found according to age group and sex crossed with age group. Research should develop in the direction of verifying which other factors should be included in order to gain a better understanding of the limits of chronological age estimation with the Demirjian standards.It is also recommended when using the Demirjian standards that raters take special caution when the estimated age falls between 10 and 11 years for boys and girls, and in girls beyond 12 years of age. Notwithstanding these caveats, the Demirjian scores have predicted the chronological ages of individuals with an acceptable degree of accuracy. The only concern is that the degree of prediction is not as high as it may appear to be when the entire population is treated as a homogeneous group, especially when compared with segmentation by age and sex groups.


The discharge characteristics and variation in active species during the plasma electrolytic oxidation (PEO) process were studied by optical emission spectroscopy. The surface morphology and element composition of the membranes were observed by scanning electron microscope. The ion transfer of the substrate was studied by atomic absorption spectroscopy. The phase composition and corrosion characteristics of the PEO membranes were examined with XRD and an electrochemical workstation, respectively. The heat and mass transfer models during the PEO process were introduced. The contributions of ions to the membranes and active species were also analyzed. The results indicated that the ion transfer at different stages exhibits different tendencies. At the first and transition stages, the migration resistance of the ions was low and increased gradually. At the initial discharge stage, the migration resistance was the highest because the highest membrane growth rate occurred at this stage. At the later discharge stage, the migration resistance tends to be stable, which is ascribed to a dynamic equilibrium PEO membrane growth rate. The intensity of active species is related to the energy state of the working electrode’s surface. The higher the energy, the greater the probability that the active species will be excited to generate energy level transitions, and the higher the plasma concentration.ZrO Plasma electrolytic oxidation (PEO) technology is an effective method for the surface modification of metallic materials. It can grow ceramic membranes on the substrate in situ due to the mutual effects of electrochemistry, plasma chemistry, and thermal chemistry. Because the chemical reaction happens between the interface of the substrate/electrolyte and the electrolyte/substrate, rather than by simple physical deposition, the membranes are strongly adhered to the substrate with different compositions, membrane thickness, colors, strength, hardness, friction property, photocatalytic activity, etc. ,2,3,4, tSome important features of the PEO process are the phenomena of fulmination, luminescence, discharge, and heat release that occur between the interfaces of substrates/electrolytes . At diffThe composition and characteristics of active species in the plasma field and their influence on the PEO process are important for understanding the mechanism of PEO. Therefore, analysis of the discharge active species in the plasma field and its thermodynamic state is of great significance.The breakdown and discharge phenomena are other important features of PEO technology that have been studied by many researchers ,7,8,9,102 membranes prepared by PEO [2 particles improved the ion exchange capacity and induced anion-selective properties on the membranes. Dzyazko [However, most research has focused on improving the performance and micro-structure of the membranes, such as the photocatalytic activity of the TiOd by PEO ,6, the nd by PEO ,9 on thed by PEO  reported2 nanoparticles on the microstructure and properties of Al2O3-TiO2 composite coatings. They discussed two growth mechanisms of the PEO process. Up to now, little research has reported the influence of the ions in the electrolyte on the heat and mass transfer between the interfaces. Further studies on the composition of plasma active species and the characteristics of micro-discharges are necessary to answer these questions.What is the influence of the ions in the electrolyte on the heat and mass transfer between the interfaces? How do the ions affect the plasma field and active species? How are the PEO membranes formed? What is the relationship between the ions and the PEO membrane composition? Wail  used ab The fast-imaging digital camera, optical emission spectroscopy (OES) and scanning electron microscope were used to further investigate the discharge mechanism of the PEO process and the influence of the anion and cation in the electrolyte on the plasma field and the PEO membranes. The influence of cations and anions on ion transfer was derived. The heat and mass transfer models and PEO membranes’ growth mechanisms were also introduced. The sources, orbit transitions, and transition orders of the active species were also discussed.2ZrF6 was 0.025 mol/L. The mole ratio of K2ZrF6 to NaH2PO4 was 9:1 to ensure the pH of the electrolytes was around 4.5. The samples were treated under a voltage of 460–470 V for 30 min. The voltage and current were recorded with a data acquisition system. The sampling period of the data was 200 ms. The reagent is from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China.The details of the PEO membrane preparation were reported in our previous studies ,5. The mThe evolution of bubbles and micro-discharges on the surface of the substrate was recorded by the digital camera’s fast imaging .The details of the active species of the micro-discharges in the plasma field formed during the PEO process were captured by optical emission spectroscopy (OES), which has been reported in our previous studies ,5. Subse2+ in electrolytes, comprising just the dissociative magnesium ions in the electrolyte. Samples were taken out after the experiments finished at every fixed voltage and reaction time. The electrolyte was mixed fully before sampling. Then the solution was diluted to certain concentrations and analyzed with AAS.AA-6800 atomic absorption spectrometry (AAS) was used to analyze the concentration of dissolved MgThe micro-morphology of the PEO membranes was observed with a scanning electron microscope (SEM)  at different voltages. The elements and content of the membranes were obtained with the energy dispersive X-ray spectroscopy (EDX) affiliated with SEM.The phase composition of the PEO membranes was analyzed by  .2. A platinum plate and a saturated calomel electrode (SCE) were used as the counter and reference electrode, respectively. The scanning rate was 1 mV/s from −1.6 V to −0.9 V versus the reference electrode.Corrosion resistance of the oxide membranes was tested by potentiodynamic polarization tests using an Autolab system  in 3.5 wt.% NaCl solution at a temperature of between 30 and 33 °C. All samples were sealed with epoxy resin, and the tested areas were 0.5 cm2ZrF6 electrolyte are shown in Voltage-time and current-time curves of the PEO process with KWhen the voltage continued to increase above the breakdown down Point D , the cur2O+ (549.3 nm), O2 (628.0 nm), and H2O (719.2 nm), which further proves that the breakdown first occurred in the bubbles of the gas envelope. As shown in At the transition stage, the collected weak spectral signals were mainly from Hand H2O 79.2 nm, w2O+ 49.3 nm, and H2O 79.2 nm, w2O+ 49.3 nm, 2ZrF6 electrolyte at the plasma discharge stage. As shown in 2 (759.37 nm), O2+ (383.05 nm), and OI (448.72 nm), as detected in the OES spectra. These atoms and molecules were mainly from the substrate and gases produced on the surface of the substrate . At the initial discharge stage, the voltage increased from 455 to 466 V, and the spectra intensity increased from 60 to over 800 a. u. At the later discharge stage, because the sparks’ density decreased and the size increased owing to the increasing thickness of the membranes and the decreasing energy on the substrate, the spectra intensity decreased gradually  was between 500–1000 a. u., while the highest intensity of active species  was between 100–300 a. u. On the one hand, the intensity differences in these species may have been due to the fact that the active species excited by the metal elements had higher concentrations in the plasma field during the discharge stage, because the minimum excitation energy was required for the metal elements, followed by the H and O elements. On the other hand, it may be related to the energy state of each of the active species. The higher the energy the active species observed, the stronger was the intensity of the spectra. The excitation level transitions and energy requirements of each active species are shown in As shown in 3 and 3 × 104 K, according to the Balmer hydrogen lines . The high-temperature environment provided the possibility for PEO ceramic membrane melting and sintering.The temperature level of the micro-discharge in the plasma field was a very important parameter. As calculated in our previous study , the cal2+ from the substrate in the electrolyte. During the conventional anodic oxidation reaction, the magnesium ions were eluted, and at this stage, Mg2+ migrated to the electrolyte in a large amount, from 0 to 68 mg/L. These results also prove that at this stage, the growth rate of the membrane was slow, and the substrate was more susceptible to ionization. Furthermore, the migration resistance was low, so it was easier for magnesium ions to migrate from the substrate to the membrane/electrolyte interfaces. At the transition stage, the amount of Mg2+ migrated from the substrate increased rapidly from 68 to 83 mg/L when the voltage was increased from 300 to 400 V. Additionally, at the transition stage, the gas envelope was broken down, followed by the breakdown of the dielectric barrier layer, so the migration resistance was also low at this stage. Therefore, the dissolution rate of the magnesium ions was also larger at the transition stage. The migrated Mg2+ continuously increased at the initial discharge stage from 83 to 89 mg/L (before 466 V-5 min), because at this stage, the large number of discharge channels made it easy for Mg2+ to migrate into the electrolyte. At the later discharge stage (after 466 V-5 min), the variation trend of migrated Mg2+ tended to be relatively stable, with the concentration remaining between 88–89 mg/L. Because the membrane’s thickness increased gradually at the later discharge stage, as discussed above in 2+ tended to be stable at the later discharge stage.2+ was produced by the anodic reaction of the substrate (reaction (1)). The cathodic reaction is shown in reaction (2).Under the electric field function, Mg62− of the K2ZrF6 electrolyte. The source of O elements was complicated; they might come from the OH− or from the O2 dissolved in the electrolyte during the PEO process, but the OH− and O2 were from the water ionization. At the conventional oxidation stage, the Mg2+ was mainly from the anodic oxidation, and then migrated into the electrolyte. The ZrF62− was also ionized, and then migrated to the electrolyte/substrate interfaces to react with the substrate at the same time. At the transition stage, the inelastic collision and electron avalanche occurred, which was another way for the Mg2+ and F− to migrate at the gas/electrolyte and substrate/gas interfaces aside from the electrode reaction. At the discharge stage, the micro-discharge channels were the main way for the ions to migrate between the gas/electrolyte and substrate/gas interfaces.The ion migration between the electrolyte/membrane interfaces was different because of the different reactions, the Joule heat, and the membrane thickness. To some extent, the composition of the membranes formed at different voltages during the PEO process reflects the ion migration between the electrolyte/membrane interfaces. The composition variation of the membranes is shown in 62− and OH− also migrated to the interfaces of the substrate/electrolyte to participate in the membrane-formation reaction. Under the high-energy conditions in the plasma field, the ZrF62− was dissociated into Zr4+ and F−, and Zr4+ underwent weak hydrolysis and ionization in water (as shown in reactions (5)). Ionized OH− would accelerate the ionization of Zr4+, leading to the deposition of Zr(OH)4 (as shown in reactions (6)). Thus, the content of Zr and O increased at this stage. At the transition stage, the content of Mg and F still decreased, while that of Zr and O increased gradually. At the initial discharge stage (before 466 V-5 min), the content of Mg and F decreased sharply, indicating that the membranes’ growth rate was much higher at this stage. The membranes’ increased growth rate resulted in the increased resistance of the Mg and F ions migrated to the substrate/electrolyte interfaces. In addition, the content of O and Zr elements increased sharply, which may be attributed to the higher concentration of ZrF62− and OH- in the electrolyte. After the gas envelope was broken down, ZrF62− and OH- migrated to the electrolyte/substrate interfaces to participate in the PEO membrane reactions (as shown in reactions (5) and (6)). At the later discharge stage (after 466 V-5 min), the variation trends of Mg, F, Zr, and O contents became smaller and smaller, which indicated that the ion migration between the substrate/electrolyte and electrolyte/substrate interfaces had reached a dynamic equilibrium. That is to say, the PEO membranes’ growth rate also reached a dynamic equilibrium at this stage.As shown in It could be concluded that at the conventional oxidation stage and transition stage, the migration resistance of the ions was low and increased gradually. At the initial discharge stage, the migration resistance was the highest because of the highest membrane growth rate. At the later discharge stage, the migration resistance tended to be stable with a dynamic equilibrium PEO membrane growth rate. Furthermore, the cations played an important role in the membranes’ composition.There are many complicated chemical processes during the PEO process, such as thermo-chemistry, plasma chemistry, and electrochemistry, etc. There are also heat- and mass-transfer behaviors between the gas/liquid, gas/solid and liquid/solid interfaces. Based on the data discussed above, the simplified heat and mass transfer models were proposed to directly demonstrate the PEO mechanism, which is shown in 2) were continuously generated on the substrate. When the energy of the surface of the whole substrate reached a certain value, water vapor (H2O) was also generated on the surface of the substrate. At this stage, the anions (X− or Y−) in the electrolyte were also aggregated toward the surface of the substrate by the function of electric field. When the applied voltage reached a certain value, under the function of the thermal radiation, the surface of the substrate emitted weak light. At the transition stage . H2O would be ionized to produce H2 and O2; O2 would be further dissociated to O, O2+ or OI; H2 would be further dissociated to produce Balmer line H). The breakdown of the gas envelope occurred at this time . The anions were accelerated by the holes created by the ruptured bubbles and moved to the surface of the substrate. This was the kinetic energy transfer e. The moCombining the results discussed in SEM of cross sections at the transition stage and the discharge stage is shown in 2 ceramic membranes. It can be seen that the PEO ceramic membrane was mainly composed of ZrO2 and a little MgF2. ZrO2 has three different crystal phases: cubic crystal phase (c-ZrO2), tetragonal crystal phase (t-ZrO2), and monoclinic crystal phase (m-ZrO2). The melting and sintering temperatures of the cubic and tetragonal crystal phases were above 1500 °C, which belongs to the high-temperature crystal phase. The presence of the high-temperature crystal phase of ZrO2 further proves that the plasma field exhibited a high-temperature environment, which provided conditions for the membrane melting and sintering and then improved the corrosion resistance of the ZrO2 ceramic membrane. The remaining XRD peaks were MgF2 peaks.2 ceramic membrane. The polarization curve was fitted according to the tafel curve-fitting software provided by the electrochemical workstation. The corrosion potential of the ZrO2 ceramic membrane was −1.29 V, the corrosion current density was 3.1 × 10−9 (A/cm2), and the corrosion resistance was 6.5 × 107 Ω. Compared to the substrate , and corrosion resistance was 109.8 Ω), the corrosion current density of the PEO ceramic membrane was improved by six orders, which is attributed to the high-temperature phase formation of the ZrO2.(1)The cations had the highest spectra intensity related to the lowest excitation energy with the higher plasma concentration. Although the anion of the electrolyte does not contribute to the composition of the plasma active species, it plays an important role in the charge balance of the entire system and the composition of the membrane layer. The intensity of active species during the PEO process is related to the energy state of the working electrode’s surface. The more energy there is, the more likely it is that the active species will be excited to generate energy level transitions.(2)The heat and mass transfer during the PEO process were analyzed, and the PEO films’ growth mechanism was also proposed. The ion transfer at different stages exhibited different tendencies. At the conventional oxidation stage and transition stage, the migration resistance of the ions was low and increased gradually. At the initial discharge stage, the migration resistance was the highest because the highest membrane growth rate occurred at this stage. At the later discharge stage, the migration resistance tended to be stable, which is ascribed to a dynamic equilibrium PEO membrane growth rate.(3)The prepared PEO ceramic membranes had a uniform surface with many different inner discharge channels distributed in the outside discharge channel. This proves that the PEO membranes grow layer by layer from the inner layer to the outer layer.(4)2 ceramic membrane was improved by six orders of magnitude compared with the AZ31B substrate, a result attributed to the high-temperature phase formation of the cubic, tetragonal, and monoclinic ZrO2.The corrosion current density of the ZrO


The extrusion of hollow profiles from hard-deformable AlZnMg alloys by using porthole dies encounters great technological difficulties in practice. High extrusion force accompanies the technological process, which is caused by high deformation resistance and high friction resistance in extrusion conditions. As a result of high thermo-mechanical loads affecting the die, a significant loss of dimensional accuracy of extruded profiles can be observed. The different projects of porthole dies for the extrusion of Ø50 × 2 mm tubes from the 7021 alloy were numerically calculated and then tested in industrial conditions by using a press of 25 MN capacity equipped with a container with a diameter of 7 inches . New extrusion die 3 with modified bridge and mandrel geometry and a special radial–convex entry to the die opening was proposed. FEM was applied to analyse the metal flow during extrusion, geometrical stability of extruded tubes and the die deflection. The photogrammetric measuring method was used to evaluate dimensional accuracy of tubes extruded in different conditions and geometrical deviations in porthole dies elements, especially the bridges and the mandrels. Research revealed a high dimensional accuracy of tubes extruded from the 6082 alloy and from the 7021 alloy by using original extrusion die 3, while much higher dimensional deviations were noted for tubes extruded from the 7021 alloy by using extrusion dies 1 and 2, particularly in relation to the circularity, centricity and wall thickness. The hollow extruded profiles from 7000 series aluminium alloys are currently used in a wide application of the construction of various means of transportation, including important automotive systems. Therefore, the profiles must fulfil high quality expectations, in particular, concerning dimensional accuracy. The extrusion of aluminium alloys becomes more difficult as its strength is increased. The 7000 series alloys not containing copper are easier to extrude compared to, e.g., high strength 7075 alloys, but the extrusion force is high, which is what implicates various dimensional defects in the extruded profiles. Additional difficulties are connected with a high friction at the tool surface, which produces non uniform metal flow from the die cavity. The extrusion parameters and the porthole die design can also have an impact on the extrudate geometry. The complex set of reasons of the geometrical defects in extrudate comprises the result from the unsuitable design of the porthole die and parameters of the whole production line, including extrusion process, heat treatment on the run-out table and stretching. In turn, the production parameters cover types of alloy, extrusion force, billet temperature, extrusion speed, rate of cooling in the quenching tunnel and force of stretching.The most important tolerance measures are as follows: wall thickness, circularity and eccentricity, convexity and concavity of the walls, angularity, straightness, bow and twist along the profile. The direct reasons for the loss of profile dimensional accuracy are as follows: elastic deflection of die, including deflection of mandrels; non-uniform metal flow within the die cavity; imperfect design of the welding chamber and bearings; die wear; non-uniform temperature distribution within the billet; too high a cooling rate within the quenching tunnel; and sometimes excessive plastic deformation during stretching. When designing the extrusion process, one should take account of the fact that tighter tolerances will push up the cost and make the production longer.When a new profile is produced, trials and corrections of the die are necessary in order to fulfil required geometrical tolerances, as well as to achieve the compromise between effectiveness, surface quality and die life. Therefore, that finite element simulation (FEM) is a useful tool for analysing the relation between the process parameters, the tool design and the profile quality.Many researchers analysed the influence of the porthole die geometry on die deflection and the resulting geometrical quality of the extruded aluminium profiles ,2,3,4,5.The influence of die deformation on the speed, temperature distribution and distortion of the two profiles from AA6082 alloy is reported and analysed in . As a coRefs. ,12 reporHsu et al.  studied Incidentally, it is worth noting that the AlZnMgCu alloys are very difficult as far as the dimensional accuracy is considered because of both the high extrusion force and deformation resistance leading to large die deflection and non-uniform metal flow. The large distortion of the rectangular hollow profile from the 6061 alloy was observed as a result of the non-uniform exit velocity . To decrThe study  presenteIn this work, the influence of different porthole die design on the metal flow during extrusion and on the dimensional accuracy of round tubes of Ø50 × 2 mm from the 6082 and 7021 alloys was investigated. The die deflection was experimentally measured for different design solutions to investigate the effect of the die deflection on the material flow. FEM simulation was applied in the design of the porthole dies and to predict the metal flow and the die deflection. The photogrammetric measuring method was used to evaluate the dimensional accuracy of tubes extruded in different conditions and the geometrical deviation of porthole dies, especially the bridges and the mandrels. The statistical correlation method was used to determine the influence of the technological parameters of the extrusion process on the dimensional accuracy of profiles. The ANOVA analysis was applied for extrusion dies.The billets of 178 mm in diameter, of which chemical compositions are presented in The QForm-Extrusion software and specially prepared material model were used to analyse the extrusion process of tubes of Ø50 × 2 mm from aluminium alloy grade 7021 (AlZnMg) using porthole dies of various geometry. Combined Lagrangian–Eulerian approach is the method that is used in QForm-Extrusion in order to describe the deformed material motion. This approach combines two basic formulations, taking advantages of both of them—from the Eulerian: adapted stationary mesh that allows improving the accuracy of metal flow prediction significantly and reduces simulation time, and from the Lagrangian: dynamically movable mesh to animate the profile flow after the bearing exit. These features, consolidated by coupled thermal and mechanical tasks available in the software, allow the obtaining of a precise distribution of the profile velocities that, in turn, means the accurate prediction of parameters defining dimensional accuracy of the extrudates.The first step in the numerical modelling FEM was preparation of proper 3D models of tools and billet using CAD Solid Works program. The geometry of the porthole die has a crucial importance from the point of view of minimum deformation resistance in the extrusion process, which, in turn, relates to minimisation of extrusion force, elastic deflection of the die, improvement in metal flow, dimensional accuracy of the profile and maximisation of the exit speed.Three different solutions of 2-hole die geometry were taken to calculation—the die with maximum opening of the inlet channels (die 1), conventional porthole die for 6xxx alloys based on the local 3-armed bridges (die 2) and die 3, which is a modified version of die 2. The geometry of die 2 was taken from extrusion industry practice for 6082 alloy. The final design of extrusion die 3 was developed based on gradual optimization of different die geometry using FEM numerical simulations based on three assumed criteria. The first criterion defined a maximum force not exceeding 25 MN. The second optimization factor minimized the elastic deflection of the die during the process, not exceeding 0.5 mm. The third criterion included ensuring an even outflow of metal from the die bearing, so the velocity deviation did not exceed ±20% of the average value. In total, almost 100 numerical FEM simulations were carried out analysing the influence of portholes, webs, cores, welding chambers, pockets and bearing geometry to determine the final specific die geometry.The massive bridges were assumed for die 1 and adapted for hard 7xxx alloys; the thickness of bridges for die 3 was increased by 4 mm, whereas their length was increased by 40 mm in relation to die 2. In addition, a radial and convex entry to cavity of die 3 was added. The thickness of bridges was equal to 28, 16 and 20 mm for die 1, die 2 and die 3, respectively; length of bridges was 70, 55 and 95 mm, whereas height of the welding chambers was 25, 30 and 27 mm. The maximal broad inlet channels, shaped pockets, bearings of varied length and proper geometry of the central baffle and mandrels were adapted for die 3. The 3D models of the porthole dies discussed and the view from the bottom are presented in The second step of the FEM modelling was preparation and implementation of the material model for the alloy 7021, which after approximation was expressed by the constitutive equation of Hansel–Spittel (Equation (1)). The starting point was the plastometric compression tests with the use of Gleeble 3800 simulator , which allowed for determining stress–true strain equation, dependent on temperature and strain rate .(1)σ=10The third step of the FEM modelling was defining of boundary conditions. Friction model used in QForm allowed for taking into account the adhesion effect between aluminium and steel. The constant shear friction law is adapted everywhere between workpiece and tool materials, except in bearings where the contact pressure is relatively low. The friction on the bearings was calculated based on the phenomenological model that includes a number of parameters, such as resulting bearings angle, pressure, etc. This approach allowed us to obtain the realistic behaviour of the metal in simulation with three possible zones: sticking, sliding, and separation zone. All the defined extrusion process parameters are presented in The extrusion trials for the round tube of Ø50 × 2 mm from the 7021 alloy with the use of the discussed porthole dies were performed on the hydraulic direct press of 25 MN capacity and equipped with container of 7″ in diameter.The conditions of the trials were identical to those in the numerical simulation for different billet heating temperature and extrusion speed. In the case of extrusion through die 3, the trials were performed for billet temperature of 480 °C and ram speed of 1.5 mm/s as a result of the experiences gained during previous extrusion with dies 1 and 2, which were also tested with higher extrusion speeds and higher billet temperatures. The run-out table of the press with the cooling system and the tested porthole dies of two holes are shown in During the trials, the following process parameters were recorded: ram speed, exit speed, extrusion pressure and profile temperature with the use of the data acquisition system.The surface quality was inspected on-line with respect of cracking or tarnish. The maximal extrusion speed was recorded when cracking on profile surface began. The samples taken from the tubes extruded with different process conditions were submitted to optical scanning to check their dimensional accuracy. Similar optical scanning was performed on the used dies and their dimensions were compared with these for new ones.The scanner GOM Atos Core 200  a was useThe first step of the dies measurements included gathering coordinates of all the selected points on the samples’ surface. Next, the detailed scanning from the different perspectives was realized to digitalize the whole available surface. Due to complicated shape of the dies, the process needed about 75 scans from each side. The surfaces of bridges, mandrels and bearing lands were inspected, in particular. The coloured maps of deviations allowed indications of the regions evidently subjected to wearing.The analysis of the results was performed with the use of Gom Inspect program, and the deviations from the nominal geometry were generated. The deviations concerned diameters, ovality, eccentricity, wall thickness and surface quality of the extruded tubes. The results were analysed and the statistical correlations was obtained using Origin Lab code. The correlation determined interactions between selected variables but did not explain the reasons or the method of their origination. A positive correlation (correlation coefficient from 0 to 1) suggested that as one feature rose, the mean values of the second increased too. A negative correlation (correlation coefficient from −1 to 0) indicated the opposite dependence. The power of correlation is defined in the following way: 0.2 poor correlation; 0.2 ÷ 0.4 low correlation (distinct dependence); 0.4 ÷ 0.6 moderate correlation (key dependence); 0.6 ÷ 0.8 high correlation (significant dependence); 0.8 ÷ 0.9 very high correlation (very high dependence); 0.9 ÷ 1.0 full dependence. In the case of dies, the results were converted to ANOVA statistics.The detailed data concerning the metal exit speed in the die cavity on the profile perimeter and elastic deflection in different regions of the mandrel for the all analysed dies are presented in The extrusion of the examined tubes was performed for die 1, die 2 and die 3 for variable heating temperatures of billet: 520 °C, 510 °C, 500 °C and 480 °C and for variable extrusion speed: 1.5 ÷ 4 mm/s. In the case of die 3, the billet temperature was of 480 °C and the extrusion speed was of 1.5 mm/s. Exemplary technological parameters of extrusion process for die 3 were shown in During the tests for die 1 and 2 and for the lowest billet temperature, the cracking of a mandrel occurred in both the tested dies and the mandrels were damaged , is also significant. Regarding the eccentricity of the tube in the case of die 1, a low acceptable value is observed even for high extrusion speeds. However, a large value of eccentricity for the tube of die 2 is observed (over 1 mm) for a low extrusion speed of 1 mm/s, which unexpectedly drops twice for high extrusion, with a speed of 4 mm/s. As reported before, a small deviation of the wall thickness below 0.1 mm for die 1 and a low extrusion speed of 1.5 mm/s occurred, whereas for a high extrusion speed of 4 mm/s the deviation slightly exceeds the permissible value of ±0.25 mm. In the case of die 2, a large deviation of the wall thickness, exceeding the acceptable limit is observed, independently of the extrusion speed . Die 3 pBased on the analysis results, a correlation coefficient was established. In particular, a coefficient from 0.6 to 1.0  was taken into consideration. The significant coefficients of correlation were indicated in red in In the case of die 2, a negative and high correlation of the extrusion speed and wall thickness is observed (correlation coefficient of—0.70), as well as the extrusion speed—inner diameter (correlation coefficient of—0.77), whereas a high correlation between extrusion speed and the outer diameter (coefficient of correlation 0.76) occurred. This means, in practice, a high decrease in the wall thickness and inner diameter, as well as an increase in the outer diameter, will cause a rise in extrusion speed. Moderate decreases in the circularity of the tube with an increase of billet temperature (correlation coefficient of—0.54) is also visible.The close-up of a chosen bridge (on the left) and a chosen mandrel (on the right) for the discussed tube from the 6082 alloy in The results from the measurements with the use of optical scanning 3D were utilized in a statistical analysis. Surfaces of the bridge part and insert die were divided between the regions in which the dimensional deviations were determined, which was the result of the matching CAD models of the dies and real scans.In the case of the bridge-part of die 1 (H90259), three crucial areas were analysed. Area 1 relates to the frontal part of the bridge. It was considered as a whole without demarking between particular apertures because of the die design, areas 2–5 concern the side surface of the channel and areas 6–7 indicate the surface of the mandrel/core land a. The laIn the case of the insert-part of die 1 (H90259), three crucial areas were analysed. Areas 1–2 indicate the frontal part of the channel, 3–4 the side surface of the channel and areas 5–6 relate to the die land. In the case of this element, the highest deviation values, at a maximum level of −0.3 mm, occur for the areas 5–6 b. The obThree regions for each die aperture were marked in the case of the bridge-part of die 2 (H90227). The area marked with 1–4 means the dimensional deviations of the channel surface, 5–8 refers to deviations from the surface of the core land and 9–12 are related to the frontal surface of the bridge a. The hiIn the case of the insert-part of die 2 (H90227), two areas were marked and analysed. Areas 1–4 indicate deviations obtained from the side surface of channels in the die insert, whereas areas 5–8 relate to quantities obtained from the die land surface b. The reThe distribution of the metal velocity during the extrusion of the tubes of Ø50 × 2 mm from a hard 7021 alloy, with the use of die 1 a, indicaIt is worth noting that the improvement of the die 1 design, aimed at the acceleration of the metal flow within outer regions of the die aperture in the sub-bridge area and connected with the extending of the welding chambers and lowering of the die lands, has proved to be unsuccessful. On the one hand, the maximum opening of the inlet channels in die 1, along with an application of the central two-ridge bridge, offered a chance for a decrease in the metal flow resistance during extrusion and to an increase in the average exit speed. On the other hand, it resulted in a non-uniform metal flow at the perimeter of the tube and, finally, impeded a loss of geometrical stability of the extruded tubes .As shown in the subsequent photogrammetric investigations, a correlation can be found between the tendency to lose roundness when using die 1 and high uniformity of the metal flow within the die aperture. In the case of die 2, where a uniform metal flow was observed b, deviatLower values of the elastic deflection of the mandrel were obtained for die 1, with bridges of 28 mm in thickness and 70 mm in length, whereas significantly higher elastic deflections occurred for die 2 of 16 mm bridge in thickness and of 55 mm in length. In addition, higher permanent deflections of bridges were measured for die 2. Consistently, the higher dimensional deviations of the wall thickness and eccentricity phenomenon of die 2 were confirmed. However, a large ovality of extruded tubes was stated for the extrusion of die 1 as a result of non-uniform metal outflow from the die opening and back bending of mandrels.The above observations suggest the inadequate porthole die design of die 1 and die 2, which were modified in terms of better metal flow control and higher strength and stiffness. The following corrections were performed to design the extrusion of die 3: slightly lowered/rounded entry to the inlet channels, the original geometry of central die compartment, thicker bridges of up to 20 mm, elongated bridges of up to 95 mm, greater height of the welding chambers of 21–25 mm, elongated mandrels of modified geometry, and radial-convex entry to the die cavity.The FEM calculations indicated lower elastic deflections of both bridges and mandrels, as well as more uniform supply of the metal to the die aperture, while also eliminating regions where the material passes from the elastic to plastic state . The industrial trials of the extrusion of the discussed tubes using modified die 3 and the subsequent 3D optical scanning of extruded tubes and used dies positively validated the established assumptions. A high compliance of extrusion force was obtained for FEM numerical calculations and experimental extrusion tests of the analysed tubes .The extrusion of tubes of Ø50 × 2 mm from the 7021 alloy with the use of the porthole dies is connected with high deformation resistance and high frictional resistance in comparison to the extrusion of analogical tubes from the 6082 alloy, which translates to higher extrusion pressures and lower metal exit speeds.High unit pressures during extrusion tubes of Ø50 × 2 leads to high thermo-mechanical loads of dies connected with permanent deflection of bridges and mandrels, which leads to significant dimensional deviations of circularity and eccentricity, exceeding standard’s limits.Strong plus correlation between extrusion speed and tube circularity, strong minus correlation of extrusion speed and the wall thickness, inner and outer diameter of tubes, and moderate minus correlations between billet heating temperature and circularity of tubes exist. This means that maximal permissible extrusion speed cannot be applied, but high billet heating temperatures should possibly be advised.The application of the modified die 3 resulted in successful control of the metal flow, which consisted in the effective facilitating of the inflow of metal to the sub-bridge areas, thus minimizing the side deviation of mandrels.The design of the porthole dies for the extrusion of the 7xxxx series aluminium alloys needs new assumptions in relation to classic dies for the extrusion of the 6xxxx series alloys. In the extrusion of tubes from a 7021 alloy, we recommend: slightly thicker and considerably elongated bridges, special central die compartment, higher welding chambers, shaped pocket dies, geometrically modified mandrels and smooth entries to the die cavity.Based on the obtained results, the following conclusions can be formulated:


First of all, the explosion-welding method was adopted to prepare steel fiber-reinforced steel-aluminum composite plates. Secondly, the smooth particle hydrodynamic (SPH) method was used to investigate the effect of introducing steel fibers to a vortex region created at the bonding interface of the steel-aluminum composite plate. Thirdly, the following conclusions were drawn through an analysis of the vortex region with the assistance of scanning electron microscopy and energy-dispersive X-ray spectroscopy. A brittle intermetallic compound FeAl was produced in the vortex region in an environment characterized by high temperature, high pressure, and high strain rate, resulting in cracks, holes and pores. In addition, the hardness of the vortex area was less than the estimated value, which is mainly because the main element in the vortex area was 2A12 aluminum with low hardness, and there were cracks, holes, pores and other defects that caused hardness reduction. Although the addition of steel fibers caused defects at the bond interface, the addition of steel fibers was effective in improving the tensile resistance performance of steel-aluminum composite panels to a certain extent. In addition, the larger the fiber diameter, the more significant the increase in tensile resistance. With the rapid development of industry, more and more regions need to produce special equipment by machining high-quality metals into sheets with excellent anticorrosion, antioxidation, and mechanical properties. If all these devices are made of high-quality metals, their costs will be inevitably high, resulting in unnecessary waste. Therefore, replacing high-quality metals with bimetallic materials is the most ideal solution. SS-304 stainless steel is characterized by high strength, impact resistance, reliable performance, and good welding and riveting performance, but it has a lot of shortcomings, such as high maintenance cost, heaviness, and large production energy consumption. However, 2A12 aluminum material has a lot of advantages, including lightness, good electrical conductivity, ease of extension, corrosion resistance, and few toxic and side effects. Bimetallic materials have the advantages of two metal components, so the application of steel-aluminum composite plates can reduce the mass of SS-304 stainless steel and improve its corrosion resistance. Explosive welding is a solid-phase welding method, which can be used for the welding of double-layer or multilayer composite plates of the same or different metals ,6. CompaExtensive studies have been conducted on steel-aluminum composite plates, with outstanding achievements. In 1983, Kotov V A studied  unidirecThe effects of steel fiber with different diameters on the interface and mechanical properties of steel-aluminum composite sheets were studied. In the early stage, the SPH method in Autodyn software was used to study the influence of high-temperature and high-pressure environments on steel fiber and composite interface to simulate the explosive welding experiment. Later, scanning electron microscopy and energy-dispersive spectroscopy were adopted to systematically study the changes in the bonding interface and the formation of intermetallic compounds after adding steel fibers. The effect of the addition of steel fiber on the hardness of the base plate was further studied by microhardness tests. Finally, a universal testing machine was used to verify the impact of the addition of steel fibers on the tensile properties of steel-aluminum composite plates.3, the explosive height is 20 mm, and the detonation velocity is 2430 m/s. The specific parameters of ANFO are shown in Ansys/Autodyn software was used to carry out simulation experiments on SS-304 and 2A12 aluminum composite plates prepared by explosive welding. The SPH method can extensively simulate large deformation problems such as disintegration, fragmentation, solid spalling, and brittle fracture of continuum structures and avoid algorithm coupling, so it is very suitable for numerical simulation of explosive welding of multilayer metal plates ,20. TherExplosive welding mainly includes: directly in the atmosphere, in water, and in rough vacuum. Compared with explosive welding experiments in low vacuum and water, explosive welding experiments in the air have a simpler assembly process, use lower detonation velocity of explosives, and are safer and more efficient. Therefore, in this paper, explosive welding experiments in the air ,22,23 wevp, the collision angle β, and the moving speed of the collision point vc. The moving speed of the collision point is equal to the detonation velocity of the explosive. Using 2# rock ammonium nitrate explosive, the parallel explosive welding experiment was used, satisfying the following relationship [vp is the impact velocity; 2E is the Gurney energy; m is the mass of the flyer plate; R is the explosion ratio; ρe is the density of the explosive; ρf is the density of the flyer plate; he is the height of the explosive; hf is the thickness of the flyer plate; C is the explosive mass per unit area; Se is the explosive area, which is the same as the surface area of the flyer plate; M is the explosive payload; vd = vc equals the detonation velocity of the explosive. Therefore, the detonation velocity is 2400 m/s [vp = 668 m/s, β = 17.5°.Explosive welding aims to connect weldments by using the impact force generated by the explosion to cause the rapid collision of the weldments. The three most critical parameters are the impact velocity of the composite plate tionship :(1)R=ρeh2400 m/s . vp = 66vp and the impact angle β meet the explosive welding window; (2) there must be jet formation when welding, so that the interface can be self-cleaning, exposing the fresh surface; and (3) a fine and uniform corrugated interface or a flat interface with sufficient strength is formed. Finally, to better understand this problem, SPH simulation was introduced to study the detailed evolution process of the steel-aluminum interface.The bonding of explosive welding is divided into three categories: (1) direct bonding of metals; (2) forming a uniform and continuous melting layer; and (3) undulate bonding, which is the most common form. In undulate bonding, because the molten material at the bonding interface is retained in the vortex and is periodically and discontinuously separated, when there is an external load, the microcrack source generated by the interface defects in the melting tank is not easily propagated. Therefore, the most ideal method is tiny undulate bonding. Many experiments and studies have shown that to realize high-quality explosive welding, the following three requirements should be met: (1) undulate bonding can be obtained under certain collision conditions, that is, the impact velocity The thermodynamic state of the explosive welding process was simulated by the SPH method to better understand the interface evolution. To further analyze the distribution of elements in the unilateral vortex area of steel fiber, 8 points were selected for EDS point scanning in this area, as shown in To further explore the impact of the addition of steel fibers on the interface of the steel-aluminum composite plate prepared by explosive welding, EDS scanning was carried out on the interface of the steel-aluminum composite plate without steel fibers and the steel-aluminum composite plate with a steel fiber diameter of 0.5 mm, and the results are shown in To explore the micromechanical properties of the steel fiber-reinforced steel-aluminum composite plate, a microhardness test of the cross-section of the steel-aluminum composite plate with a steel fiber diameter of 0.5 mm was carried out. The corresponding test area was divided into five parts, as shown in σ is the tensile strength, F is the loading load, and S is the stressed area of the sample.A 0.5 mm notch was opened on one side of the sample to measure the tensile strength of the sample, then the impact of the addition of steel fibers on the tensile properties of steel-aluminum composite plates prepared by explosive welding was explored. Three specimens were taken in the steel fiber parallel to the tensile load direction and the steel fiber perpendicular to the tensile load direction. The specific location and size parameters of the sample are shown in − and 5+ samples, and the fiber diameters in 2− and 6+, 3− and 7+, 4− and 8+ samples were 0.25 mm, 0.35 mm, and 0.5 mm, respectively. To ensure the accuracy of the experimental data, each sample of the steel fiber parallel to the tensile load direction contained four steel fibers.The samples in each group were from the same position in the center of four steel-aluminum composite plates prepared by explosive welding, aiming to avoid the influence of boundary effect on tensile samples. In − was 420.53 MPa. The average tensile strength of sample 2− increased by 8.5% compared with sample 1−, with the highest increase of 9.8% and the lowest increase of 7.0%; the average tensile strength of sample 3− increased by 15.4% compared with sample 1−, with the highest increase of 18.3% and the lowest increase of 13.8%. The average tensile strength of sample 4− increased by 33.7% compared with sample 1−, with the highest increase of 38.6% and the lowest increase of 29.9%. In the direction of the steel fiber perpendicular to the tensile load, the average tensile resistance of sample 5+ was 435.48 MPa, and the average tensile resistance strength of sample 6+ was 2.9% higher than that of sample 5+, with the highest increase of 3.5% and the lowest increase of 2.2%. Compared with sample 5+, the average tensile resistance strength of sample 7+ increased by 6.5%, with the highest increase of 8.9% and the lowest increase of 2.2%. Compared with sample 5+, the average tensile resistance strength of sample 8+ increased by 11.2%, with the highest increase of 14.8% and the lowest increase of 8.4%. The main difference between samples 1−, 2−, 3−, 4− and samples 5+, 6+, 7+, 8+ was that the first four groups of samples were parallel to the direction of the tensile load and along the direction of the detonation wave propagation, while the last four groups were perpendicular to the direction of the tensile load and the detonation wave propagation. Among them, the sample groups 1− and 5+ were from the steel-aluminum composite plates without steel fibers. When the highest and lowest tensile resistance properties were removed from the two groups of data, they were 435.35 MPa and 438.93 MPa, respectively. The difference in the tensile resistance between the two groups could be neglected, so the influence of the propagation direction of the detonation wave on the tensile resistance was excluded. In summary, the addition of steel fibers could improve the tensile resistance of steel-aluminum composite plates prepared by explosive welding. With the increase in steel fiber diameter, the tensile resistance strength increased gradually. Agraw Ryuichi [SEM was used to analyze the fracture of the tensile specimen and study the failure mechanism of steel fiber-reinforced steel-aluminum composite plates. The steel fiber-reinforced steel-aluminum composite plate was successfully prepared by explosive welding, and the interface evolution mechanism of the steel-aluminum composite interface after adding steel fiber was simulated by the SPH method. Then, steel fiber-reinforced steel-aluminum composite plates were further studied using SEM, EDS, and tensile tests, and the following conclusions were drawn.(1)The SPH simulation method proved that there was a certain angle formed by the steel fiber, the base plate, and the composite plate, which blocked the direction of the jet so that the jet accumulated on one side of the steel fiber to form an environment with high temperature, high pressure, and high strain rate, thereby forming a vortex area. The residual stress of the jet particles in the vortex region forced them to undergo strong stirring, producing cracks, holes, and air pores in the vortex region.(2)SEM and EDS analysis proved the following two points. 1. The main reason for cracks, holes, and air pores in the vortex area was the formation of a large number of brittle intermetallic compounds, and the brittle intermetallic compound was mainly FeAl. 2. due to the blocking effect of steel fiber on the jet, the transition of elements at the interface of the composite plate with steel fiber was relatively fast.(3)Microhardness test results revealed that the cracks, holes, and air pores in the vortex region influenced the microhardness of the bonding interface to a certain extent. As the microhardness of 2A12 aluminum was relatively small, the microhardness increased with the decrease in 2A12 aluminum content in the vortex region.(4)The tensile test on the universal specimen machine proved that adding steel fibers could improve the antitensile properties of the steel-aluminum composite plates. The larger the diameter of steel fiber, the more obvious the tensile properties are. The main reason is that the steel fiber material is S20910 stainless steel, which was significantly strengthened during the explosion process.(5)Fracture morphology analysis indicated that 2A12 aluminum had a typical ductile fracture. The ductile fracture far from the bonding interface was more obvious because of explosion strengthening. The SS-304 stainless steel layer and steel fiber were quasi-cleavage fractures, and the steel fibers showed a necking phenomenon during fracture.


After this article  was publThe corresponding author provided the original underlying images and quantitative data to support several figures in the article , but staOverall, the data provided resolved some but not all of the image integrity concerns.Specifically:In the left western blot panel in In the right western blot panel in The images provided in For Figures S2B and S6, the original data  clarifieFor Figure S3, the authors stated that the original data are no longer available and so we were unable to resolve the concerns about the published figure. However, the authors provided replication data  that supWhen levels are adjusted to visualise background, there appear to be discontinuities suggestive of image splicing in Figures S2A, S2B, S3, and S6. In Figure S3 the M lanes in the left and centre blots appear similar.During our assessment of this case, faint bands were noted in the original image  for the The authors stand by the conclusions of the study and consider that the additional data provided support all original claims. The corresponding author has provided a revised schematic for PLOS Biology concluded that the article’s main conclusions appear to be supported. However, in light of the unresolved issues and the extent of concerns about the integrity of image data reported in the article, the PLOS Biology Editors issue this Expression of Concern.Overall, S1 File(ZIP)Click here for additional data file.S2 File(ZIP)Click here for additional data file.