The Portevin-Le Chatelier (PLC) effect means serrated yielding or jerky flow phenomenon in some alloys. In this paper a macroscopic model is developed to investigate the PLC effect with the emphasis on mechanical resp...The Portevin-Le Chatelier (PLC) effect means serrated yielding or jerky flow phenomenon in some alloys. In this paper a macroscopic model is developed to investigate the PLC effect with the emphasis on mechanical response of the structure evolution on microscopic scale. In addition to the normal work hardening effect, the model takes account of the thermal activation of dislocation moving with the aid of stress and the collective interactions between mobile dislocations and solute atoms due to dynamic strain ageing (DSA). It can satisfy the negative strain rate sensitivity of flow stress, which is believed to be one of the most special features associated with the PLC effect. The heterogeneous nature of the deformed material is also considered by introducing a nonuniform spatial distribution of some model parameters. The serrated yielding and localized deformation behavior can be successfully reproduced via numerical simulation based on this model.展开更多
In this study,the high-temperature stability and the generation mechanism of the Portevin-Le Chatelier(PLC)effect in solid-solution Mg-1Al-12Y alloy with different heat treatment processes were investigated by adjusti...In this study,the high-temperature stability and the generation mechanism of the Portevin-Le Chatelier(PLC)effect in solid-solution Mg-1Al-12Y alloy with different heat treatment processes were investigated by adjusting the content of long-period stacking ordered(LPSO)phases.It was found that the content of LPSO phases in the alloys differed the most after heat treatment at 530℃for 16 h and 24 h,with values of 13.56%and 3.93%respectively.Subsequently,high-temperature tensile experiments were conducted on these two alloys at temperatures of 150℃,200℃,250℃,and 300℃.The results showed that both alloys exhibited the PLC effect at temperatures ranging from 150 to 250℃.However,at a temperature 300℃,only the alloy with a greater concentration of LPSO phases exhibited the PLC effect,whereas the alloy with a lower proportion of LPSO phases did not exhibit this phenomenon.Additionally,both alloys exhibited remarkable high-temperature stability,with the alloy containing a greater percentage of LPSO phases also demonstrating superior strength.The underlying mechanism for this phenomenon lies in the exceptional high-temperature stability exhibited by the second phase within the alloy.Furthermore,the LPSO phase effectively obstructs the movement of dislocations,and it also undergoing kinking to facilitate plastic deformation of the alloy.The results indicate that the PLC effect can be suppressed by reducing dislocation pile-up at grain boundaries,which leads to a decrease in alloy plasticity but an increase in strength.The presence of the PLC effect in the WA121 alloy is attributed to the abundant dispersed second phase within the alloy,which initially hinders the movement of dislocations,leading to an increase in stress,and subsequently releases the dislocations,allowing them to continue their movement and thereby reducing in stress.展开更多
In this paper, solute concentration and precipitate content in A2024 aluminum alloy are adjusted by solution treatment （ST） at different temperatures and tensile experiments on these treated specimens are carried ou...In this paper, solute concentration and precipitate content in A2024 aluminum alloy are adjusted by solution treatment （ST） at different temperatures and tensile experiments on these treated specimens are carried out. It is found that the temperature of solution treatment （ST temperature） has a remarkable influence on the amplitude of the serrated flow and the propagation characteristics of shear bands. These results are due to the effects of solute atoms and precipitates on dynamic strain aging （DSA）. When ST temperature is higher than 300 ℃, solute concentration is relatively high and solute cloud is a key factor of DSA. When ST temperature is lower than 300 ℃, precipitate content is relatively high and the mechanism of DSA is determined by precipitates.展开更多
The effects of alloying elements and processing parameters on the mechanical properties and Portevin-Le Chatelier effect of A1-Mg alloys developed for inner auto body sheets were investigated in detail. Tensile testin...The effects of alloying elements and processing parameters on the mechanical properties and Portevin-Le Chatelier effect of A1-Mg alloys developed for inner auto body sheets were investigated in detail. Tensile testing was performed in various Zn and Mg contents under different annealing and cold-rolling conditions. In the results, the stress drop and reloading time of serrations increase with increasing plastic strain and exhibit a common linear relationship. The increase rates of stress drop and reloading time increase with increasing Mg or Zn content. The alloys with a greater intensity of serrated yielding generally exhibit a greater elongation. The stress drop and reloading time of serrations decrease with increasing grain size in the case of the annealed samples. The cold-rolled sample exhibits the most severe serra- tion because it initially contains a large number of grain boundaries and dislocations.展开更多
In the alloy with solute content higher than the limiting solubility,the solute atoms that have failed to dissolve will precipitate from the solid solution and form precipitations.In this study, the Portevin-Le Chatel...In the alloy with solute content higher than the limiting solubility,the solute atoms that have failed to dissolve will precipitate from the solid solution and form precipitations.In this study, the Portevin-Le Chatelier(PLC) effects in annealed 5456 and 5052 aluminum alloys with different precipitation contents have been investigated under different applied strain rates.The results suggest that precipitations have significant effect on the PLC effect and the more the precipitations are, the greater the influence is.Furthermore,the solute diffusion is pipe diffusion in 5052 alloy with lower precipitation content.However,for 5456 alloy with higher precipitation content,the diffusion is no longer the case but more complex.展开更多
The plastic deformation showing instability has been a subject receiving considerable attention for centuries due to its importance in many industrial processes.For Al alloys,the major instability is the Portevin-Le C...The plastic deformation showing instability has been a subject receiving considerable attention for centuries due to its importance in many industrial processes.For Al alloys,the major instability is the Portevin-Le Chatelier(PLC)effect that appears within a certain region of strain,strain rate and temperature.It manifests itself on the stress−strain curve as serrations associating with the rapid accumulation of plastic deformation within inclined slip bands.The PLC effect has severe practical consequences,which damages the surface quality after the sheet metal forming process and threatens the tensile ductility.Therefore,it is crucial to investigate the fundamental mechanisms underlying the PLC effect and in particular to investigate how it can be tempered by tailoring the material microstructure.In this paper,we review the common interpretations of the PLC effect and summarize the experimental results of the effects of the precipitation and the grain refinement,two conventional strengthening methodologies in Al alloys,on the serrated plastic flow.The effectiveness of solute atom clusters in suppressing the PLC effect is emphasized.展开更多
Portevin-Le Chatelier (PLC) effect in a severely cold-rolled Al-Zn-Mg-Cu-Zr aluminum alloy (AA7055 type) plate before and after annealing was investigated. The results show that the sample annealed at 300 ℃ undergoes...Portevin-Le Chatelier (PLC) effect in a severely cold-rolled Al-Zn-Mg-Cu-Zr aluminum alloy (AA7055 type) plate before and after annealing was investigated. The results show that the sample annealed at 300 ℃ undergoes PLC effect,whereas the PLC effect is not observed in the deformed sample or the samples annealed at 110 ℃ or 200 ℃. The main precipitates in the sample annealed at 300 ℃ are the coarsened η phases,while a mixture of small η' phases and η phases dominates in the sample annealed at 200 ℃. In the deformed sample and sample annealed at 110 ℃,GP zone are the main precipitates. The different flow behaviors are ascribed to the type of precipitates as well as the dislocation density differences.展开更多
Plastic instability, called Portevin-Le-Chatelier(PLC) effect, manifests itself as an unstable plastic flow during tensile tests of structural materials. This phenomenon has a strong influence on diverse properties, l...Plastic instability, called Portevin-Le-Chatelier(PLC) effect, manifests itself as an unstable plastic flow during tensile tests of structural materials. This phenomenon has a strong influence on diverse properties, leading to unexpected vulnerabilities in the service environment.Among various magnesium-based alloys, PLC phenomenon is most prominently observed in the Mg-Mn-Nd alloy under elevated temperature and low strain rate conditions. An important aim of the study is to clarify and compare the significance of the RE and Ca addition, which are known to cause a formation of a largely weakened non-basal type texture, in the occurrence of plastic instability. Due to the PLC phenomenon, there is a risk of weakening texture and formability improvement by the addition of RE and Ca elements in Mg alloys. Based on the understanding of the role of Nd to the PLC phenomenon in Mg-Mn alloy identified in previous studies, the PLC characteristics according to alloying elements and deformation conditions were compared and analyzed. To identify the micromechanical mechanisms of the PLC phenomenon, varies in the microstructure and mechanical properties during deformation of Mg-Mn binary and Ca or Nd-containing Mg-Mn-based ternary alloys in various conditions were systemically analyzed. The addition of Ca did not show a marked PLC effect due to the formation of low number density Mn-Ca and Ca-Ca solute clusters and an unbalanced Mn:Ca ratio. In contrast, the addition of Nd leads to the formation of a higher number density of Nd-Nd and Mn-Nd solute clusters than that of Ca-Ca and Mn-Ca solute clusters of the Mg-Mn-Ca alloy, resulting in a stable solute-dislocation interaction atmosphere under specific ranges of deformation temperature and strain rate. The deformation in the regime of PLC phenomenon, results in a decrease in ductility and an increase in strength, despite deformation at elevated temperatures with maintaining the weakened texture.展开更多
According to the deformation state in skin stretch forming, an experiment was investigated to determine the critical strain, which make the slip line occur, and the strain criteria under different strain paths are obt...According to the deformation state in skin stretch forming, an experiment was investigated to determine the critical strain, which make the slip line occur, and the strain criteria under different strain paths are obtained. The uniaxial tension tests of different specimens were carried out to determine the critical strains of different strain paths. Then, the slip line limited curve(SLC) is available from these critical strains. Two kinds of aluminum alloys, 2024-T3 and 2524-T3, were studied, and two SLCs are gained. The application of the SLC to an airplane skin stretch forming simulation was investigated, and the results show that the SLC can be used to control the slip lines occurring in practice.展开更多
基金This work was supported by the National Natural Seience Foundation of China under gran No.10372098 and 10232030.We would also like to thank the Lab of Mechanical&Materials Science of USTC for their help in the experiments on MTS
文摘The Portevin-Le Chatelier (PLC) effect means serrated yielding or jerky flow phenomenon in some alloys. In this paper a macroscopic model is developed to investigate the PLC effect with the emphasis on mechanical response of the structure evolution on microscopic scale. In addition to the normal work hardening effect, the model takes account of the thermal activation of dislocation moving with the aid of stress and the collective interactions between mobile dislocations and solute atoms due to dynamic strain ageing (DSA). It can satisfy the negative strain rate sensitivity of flow stress, which is believed to be one of the most special features associated with the PLC effect. The heterogeneous nature of the deformed material is also considered by introducing a nonuniform spatial distribution of some model parameters. The serrated yielding and localized deformation behavior can be successfully reproduced via numerical simulation based on this model.
基金supported by the Qinghai Provincial Science and Technology Department Basic Research Program(No.2023-ZJ-913M).
文摘In this study,the high-temperature stability and the generation mechanism of the Portevin-Le Chatelier(PLC)effect in solid-solution Mg-1Al-12Y alloy with different heat treatment processes were investigated by adjusting the content of long-period stacking ordered(LPSO)phases.It was found that the content of LPSO phases in the alloys differed the most after heat treatment at 530℃for 16 h and 24 h,with values of 13.56%and 3.93%respectively.Subsequently,high-temperature tensile experiments were conducted on these two alloys at temperatures of 150℃,200℃,250℃,and 300℃.The results showed that both alloys exhibited the PLC effect at temperatures ranging from 150 to 250℃.However,at a temperature 300℃,only the alloy with a greater concentration of LPSO phases exhibited the PLC effect,whereas the alloy with a lower proportion of LPSO phases did not exhibit this phenomenon.Additionally,both alloys exhibited remarkable high-temperature stability,with the alloy containing a greater percentage of LPSO phases also demonstrating superior strength.The underlying mechanism for this phenomenon lies in the exceptional high-temperature stability exhibited by the second phase within the alloy.Furthermore,the LPSO phase effectively obstructs the movement of dislocations,and it also undergoing kinking to facilitate plastic deformation of the alloy.The results indicate that the PLC effect can be suppressed by reducing dislocation pile-up at grain boundaries,which leads to a decrease in alloy plasticity but an increase in strength.The presence of the PLC effect in the WA121 alloy is attributed to the abundant dispersed second phase within the alloy,which initially hinders the movement of dislocations,leading to an increase in stress,and subsequently releases the dislocations,allowing them to continue their movement and thereby reducing in stress.
基金supported by the National Natural Science Foundation of China (Grant Nos 10872189 and 10732080)
文摘In this paper, solute concentration and precipitate content in A2024 aluminum alloy are adjusted by solution treatment （ST） at different temperatures and tensile experiments on these treated specimens are carried out. It is found that the temperature of solution treatment （ST temperature） has a remarkable influence on the amplitude of the serrated flow and the propagation characteristics of shear bands. These results are due to the effects of solute atoms and precipitates on dynamic strain aging （DSA）. When ST temperature is higher than 300 ℃, solute concentration is relatively high and solute cloud is a key factor of DSA. When ST temperature is lower than 300 ℃, precipitate content is relatively high and the mechanism of DSA is determined by precipitates.
基金financially supported by the National Natural Science Foundation of China(No.51301017)the Fundamental Research Funds for the Central Universities of China(No.FRF-TP-13-034A)
文摘The effects of alloying elements and processing parameters on the mechanical properties and Portevin-Le Chatelier effect of A1-Mg alloys developed for inner auto body sheets were investigated in detail. Tensile testing was performed in various Zn and Mg contents under different annealing and cold-rolling conditions. In the results, the stress drop and reloading time of serrations increase with increasing plastic strain and exhibit a common linear relationship. The increase rates of stress drop and reloading time increase with increasing Mg or Zn content. The alloys with a greater intensity of serrated yielding generally exhibit a greater elongation. The stress drop and reloading time of serrations decrease with increasing grain size in the case of the annealed samples. The cold-rolled sample exhibits the most severe serra- tion because it initially contains a large number of grain boundaries and dislocations.
基金The financial support received from the National Natural Science Foundation of China under Grant Nos. 10732080,10872189
文摘In the alloy with solute content higher than the limiting solubility,the solute atoms that have failed to dissolve will precipitate from the solid solution and form precipitations.In this study, the Portevin-Le Chatelier(PLC) effects in annealed 5456 and 5052 aluminum alloys with different precipitation contents have been investigated under different applied strain rates.The results suggest that precipitations have significant effect on the PLC effect and the more the precipitations are, the greater the influence is.Furthermore,the solute diffusion is pipe diffusion in 5052 alloy with lower precipitation content.However,for 5456 alloy with higher precipitation content,the diffusion is no longer the case but more complex.
基金Projects(52001249,51761135031,51790482,51722104)supported by the National Natural Science Foundation of ChinaProject(2017YFB0702301)supported by the National Key Research and Development Program of ChinaProject(2019M653595)supported by the China Postdoctoral Science Foundation。
文摘The plastic deformation showing instability has been a subject receiving considerable attention for centuries due to its importance in many industrial processes.For Al alloys,the major instability is the Portevin-Le Chatelier(PLC)effect that appears within a certain region of strain,strain rate and temperature.It manifests itself on the stress−strain curve as serrations associating with the rapid accumulation of plastic deformation within inclined slip bands.The PLC effect has severe practical consequences,which damages the surface quality after the sheet metal forming process and threatens the tensile ductility.Therefore,it is crucial to investigate the fundamental mechanisms underlying the PLC effect and in particular to investigate how it can be tempered by tailoring the material microstructure.In this paper,we review the common interpretations of the PLC effect and summarize the experimental results of the effects of the precipitation and the grain refinement,two conventional strengthening methodologies in Al alloys,on the serrated plastic flow.The effectiveness of solute atom clusters in suppressing the PLC effect is emphasized.
基金Project(2005CB23705) supported by the National Basic Research Program of China
文摘Portevin-Le Chatelier (PLC) effect in a severely cold-rolled Al-Zn-Mg-Cu-Zr aluminum alloy (AA7055 type) plate before and after annealing was investigated. The results show that the sample annealed at 300 ℃ undergoes PLC effect,whereas the PLC effect is not observed in the deformed sample or the samples annealed at 110 ℃ or 200 ℃. The main precipitates in the sample annealed at 300 ℃ are the coarsened η phases,while a mixture of small η' phases and η phases dominates in the sample annealed at 200 ℃. In the deformed sample and sample annealed at 110 ℃,GP zone are the main precipitates. The different flow behaviors are ascribed to the type of precipitates as well as the dislocation density differences.
基金financial support of German Research Foundation (DFG)(Grant Nr. YI103/3-1 and AL1343/8-1)。
文摘Plastic instability, called Portevin-Le-Chatelier(PLC) effect, manifests itself as an unstable plastic flow during tensile tests of structural materials. This phenomenon has a strong influence on diverse properties, leading to unexpected vulnerabilities in the service environment.Among various magnesium-based alloys, PLC phenomenon is most prominently observed in the Mg-Mn-Nd alloy under elevated temperature and low strain rate conditions. An important aim of the study is to clarify and compare the significance of the RE and Ca addition, which are known to cause a formation of a largely weakened non-basal type texture, in the occurrence of plastic instability. Due to the PLC phenomenon, there is a risk of weakening texture and formability improvement by the addition of RE and Ca elements in Mg alloys. Based on the understanding of the role of Nd to the PLC phenomenon in Mg-Mn alloy identified in previous studies, the PLC characteristics according to alloying elements and deformation conditions were compared and analyzed. To identify the micromechanical mechanisms of the PLC phenomenon, varies in the microstructure and mechanical properties during deformation of Mg-Mn binary and Ca or Nd-containing Mg-Mn-based ternary alloys in various conditions were systemically analyzed. The addition of Ca did not show a marked PLC effect due to the formation of low number density Mn-Ca and Ca-Ca solute clusters and an unbalanced Mn:Ca ratio. In contrast, the addition of Nd leads to the formation of a higher number density of Nd-Nd and Mn-Nd solute clusters than that of Ca-Ca and Mn-Ca solute clusters of the Mg-Mn-Ca alloy, resulting in a stable solute-dislocation interaction atmosphere under specific ranges of deformation temperature and strain rate. The deformation in the regime of PLC phenomenon, results in a decrease in ductility and an increase in strength, despite deformation at elevated temperatures with maintaining the weakened texture.
基金Project(K0604020509) supported by Chengdu Aircraft Industrial Co. Ltd and National Foundation of Research of China
文摘According to the deformation state in skin stretch forming, an experiment was investigated to determine the critical strain, which make the slip line occur, and the strain criteria under different strain paths are obtained. The uniaxial tension tests of different specimens were carried out to determine the critical strains of different strain paths. Then, the slip line limited curve(SLC) is available from these critical strains. Two kinds of aluminum alloys, 2024-T3 and 2524-T3, were studied, and two SLCs are gained. The application of the SLC to an airplane skin stretch forming simulation was investigated, and the results show that the SLC can be used to control the slip lines occurring in practice.
