The tensile tests of the extruded ZK60 Mg containing a longitudinal weld seam were carried out at room and elevated temperatures, and the effects of induced microstructure inhomogeneity on tensile deformation behavior...The tensile tests of the extruded ZK60 Mg containing a longitudinal weld seam were carried out at room and elevated temperatures, and the effects of induced microstructure inhomogeneity on tensile deformation behavior was clarified. The results show that the deformation mode, dynamic recrystallization(DRX), texture evolution and mechanical properties are strongly affected by the longitudinal weld seam,temperature, and loading direction. The room temperature(RT) deformation of welding zone is controlled by the dislocation slips with the association of some twins, while twinning plays significant roles in the accommodation of c-axis strain of the coarse grains on matrix zone.The deformation at RT stretched along extrusion direction(ED) and transverse direction(TD) are controlled by basal slip/twinning and basal slip/prismatic slip/twinning, respectively. During high temperature tension, the dislocation cross slip of pyramidal slip is activated, and grain boundary sliding occurred in welding zone, leading to the superplastic behavior. With the increase of tensile temperature, the predominant DRX mode is transformed from continuous DRX to discontinuous DRX. Moreover, the basal poles of the grains spread from TD towards ED with the decrease of maximum pole intensity when stretched along ED, while non-basal textures are transformed to (10-10) fiber texture when stretched along TD. The slip-dominated flow is seen during RT tension along ED, while twinning becomes predominant during RT tension along TD. The fine grain structure causes the superior RT tensile properties along ED of welding zone with ultimate tensile strength of 315 MPa and elongation to failure of 13.8%. With the increase of tensile temperature, the slipping-dominated deformation is transformed into twinning-dominated, causing the decrease of strength and increase of elongation.展开更多
Al/Mg/Al sheet with good bonding quality and mechanical properties was fabricated based on the proposed porthole die co-extrusion and forging(PCE-F)process.There were no voids,cracks or other defects on the Al/Mg inte...Al/Mg/Al sheet with good bonding quality and mechanical properties was fabricated based on the proposed porthole die co-extrusion and forging(PCE-F)process.There were no voids,cracks or other defects on the Al/Mg interface.A continuous diffusion zone with two-sub-layer structure was formed across the Al/Mg interface,and its width increased with higher temperature or reduction ratio.The sub-layers formed at low and high temperature were identified to be solid solutions and intermetallic compounds(IMCs)including y-MgpAl^and^-Al3Mg.In Al layer,the welding zone mainly consisted of fine equiaxed grains with several coarse elongated grains,while the majority of matrix zone is coarse elongated grains.The rolling textures were dominated in both welding and matrix zones.In Mg layer,the welding zone exhibited complete DRXed grain structure,while several unDRXed coarse grains were observed in the matrix zone.With the increasing temperature,the grain size of Al and Mg layer firstly decreased and then increased.High reduction ratio strongly refined the grain structure of Al layer,while slightly affected the Mg layer.The Al/Mg/AI sheet experienced stress-drops twice during the tensile test.The first stress-drop was determined by the IMCs and microstructure of Mg layer,while the second stress-drop was closely related to the microstructure of Al layer.Al/Mg/Al sheet forged at the lowest temperature without the formation IMCs exhibited the highest stress for the first stress-drop,and that forged under the highest reduction ratio with the smallest grain size in Al layer had the highest stress for the second stress-drop.展开更多
The microstructure evolution of Mg-5.65 Zn-0.66 Zr(wt.%)alloy was studied based on the hot compression tests.The results indicated that the flow stress increased rapidly to a peak point at the initial stage,and then i...The microstructure evolution of Mg-5.65 Zn-0.66 Zr(wt.%)alloy was studied based on the hot compression tests.The results indicated that the flow stress increased rapidly to a peak point at the initial stage,and then it gradually decreased.Moreover,high temperature and low strain rate resulted in the decreasing of flow stress.All samples exhibited a necklace grain structure because of the occurrence of partial dynamic recrystallization(DRX).High temperature increased both the size and fraction of DRXed grains,while high strain rate showed an opposite tendency.At the conditions of 350°C/0.001 s^(-1)and 350°C/0.1 s^(-1),the twins were not exhibited and DRX played a dominant role.Importantly,the obvious split of basal texture was observed.The pyramidal<c+a>slip with high value of Schmid factor was active in large deformed grains,which corresponded to the peak split point in(0001)pole figure.A mechanism about the grain rotation was proposed to explain the relationship between the pyramidal slip and the split of basal texture.Finally,it was found that large number of{10–12}extension twins were formed during the initial stage at condition of 300°C/1 s^(-1),and the number of twins decreased with the increase of strain.The twins greatly contributed to the fast formation of basal texture and grain rotation.Moreover,the non-basal slips were active in twining region,which could facilitate the nucleation of DRX.展开更多
Abnormal grain growth(AGG)easily takes place in Mg alloys during high-temperature solutions,result-ing in deterioration of mechanical properties.Hence,the compression prior to solution(pre-compression)was conducted to...Abnormal grain growth(AGG)easily takes place in Mg alloys during high-temperature solutions,result-ing in deterioration of mechanical properties.Hence,the compression prior to solution(pre-compression)was conducted to suppress AGG,and the microstructure evolution as well as suppressing mechanisms was investigated based on quasi-in-situ analysis.After compression along the transverse direction,<11-20>//ED grains preferentially nucleated and rapidly grew up,and the initial<10-10>//ED texture was weakened.Two grain growth modes of heat-induced and strain-induced grain boundary migrations were found.The former was attributed to the high interfacial energy of grain boundaries with large curvature.The latter consumed the adjacent grains with high storage energy,forming abnormal grains with irregular shapes.The compression with a reduction>6%could obviously suppress AGG.The suppressing effects were mainly attributed to weakening the size advantage of<11-20>//ED grains,increasing nucleation,reducing grain boundary character distribution,and redistributing storage energy distribution.After 12%compression along the transverse direction,30°misorientation of<11-20>//ED grains and high energy grain boundaries were reduced.The{10-12}tensile twins and{10-15}high index twins induced by com-pression increased the nucleation of static recrystallization.Beside,compression introduces high-density dislocations,which also contributed to suppressing AGG behavior during solution.展开更多
The pre-tension was induced to suppress the abnormal grain growth(AGG)of ZK60 Mg profile during solution treatment.The effects of pre-tension on the microstructure evolution and mechanical properties were studied,and ...The pre-tension was induced to suppress the abnormal grain growth(AGG)of ZK60 Mg profile during solution treatment.The effects of pre-tension on the microstructure evolution and mechanical properties were studied,and the suppressing mechanism was discussed.If the pre-tension strain was larger than 10%,AGG during solution could be effectively inhibited,resulting in a sharp decrease in the grain size.The suppression effects were realized by restricting the orientation dependent of AGG and promoting static recrystallization.The pre-tension reset the distributions of stored energy and sizes of the grains with〈11–20〉and〈10–10〉orientations,and thus retarded the orientation dependent of AGG.Moreover,the pre-tension introduced a mass of dislocations,twins,and stacking faults,all of which promoted the occurrence of static recrystallization,and the grain structure was further refined.The pre-tension accelerated the precipitation kinetics during aging,resulting in fine and dense precipitates.With the increase of pre-tension strain,the strength of ZK60 Mg profile monotonically increased.展开更多
In this paper,a comparative study on the spray deposited and as-cast 2195 alloy was carried out to reveal their microstructure evolutions and differences during the homogenization process.The dissolution of the second...In this paper,a comparative study on the spray deposited and as-cast 2195 alloy was carried out to reveal their microstructure evolutions and differences during the homogenization process.The dissolution of the secondary particles and the diffusion of solute were studied based on microstructure characterization and kinetics analysis.The precipitation behavior of Al3Zr dispersoids and its influence on recrystallization were investigated by using TEM and EBSD characterization.It was found that the large-size particles at triangular grain boundaries dissolve slower than the intragranular phases and other grain boundary phases.The required homogenization time depends on the dissolution processes of the large-size phases at grain boundaries.The size of grain boundary phases in the spray deposited alloy is much smaller than that in the as-cast alloy,so the homogenization time required for the spray deposited alloy is significantly shorter.Two-stage and ramp heating homogenization processes can promote the precipitation of Al3Zr dispersoids in the two alloys.In the spray deposited alloy,the dispersoids tend to precipitate at the positions of the T1 plates dissolved,which causes a non-uniform distribution and decreases the recrystallization resistance of the alloy.However,the distribution of the dispersoids in the as-cast alloy is more uniform after the homogenization,which brings a stronger inhibition on the recrystallization.According to the microstructural characterization and kinetics analysis results,it can be concluded that the homogenization with a slow ramp heating is suitable for the two 2195 alloys,and a shorter holding time can be used for spray deposited alloy,e.g.12 h at 500℃,while the holding time for the as-cast alloy is no less than 35 h at 500℃.展开更多
Porthole die extrusion of Mg alloys was studied by means of experimental and numerical studies. Results indicated that an inhomogeneous microstructure formed on the cross-section of the extruded profile. On the profil...Porthole die extrusion of Mg alloys was studied by means of experimental and numerical studies. Results indicated that an inhomogeneous microstructure formed on the cross-section of the extruded profile. On the profile surface, abnormal coarse grains with an orientation of <11-20> in parallel to ED(extrusion direction) appeared. In the profile center, the welding zone was composed of fine grains with an average size of 4.19 um and an orientation of <10-10> in parallel to ED, while the matrix zone exhibited a bimodal grain structure. Disk-like, near-spherical and rod-like precipitates were observed, and the number density of those features was lower on the profile surface than that in the profile center. Then, the formation and evolution of coarse grains on the profile surface were investigated, which were found to depend on the competition between static recrystallization and grain growth. The stored deformation energy was the factor dominating the surface structure through effective regulation over nucleation of the precipitates and recrystallization. A profile with a low stored deformation energy suppressed formation of precipitates and consequently facilitated grain growth rather than recrystallization, resulting in the formation of abnormal coarse grains. Finally, the surface coarse grains contributed detrimentally to hardness, tensile properties, and wear performance of the bulk structure.展开更多
基金the financial support from the National Natural Science Foundation of China (51875317,52222510)Key Research and Development Program of Shandong Province (2021ZLGX01)。
文摘The tensile tests of the extruded ZK60 Mg containing a longitudinal weld seam were carried out at room and elevated temperatures, and the effects of induced microstructure inhomogeneity on tensile deformation behavior was clarified. The results show that the deformation mode, dynamic recrystallization(DRX), texture evolution and mechanical properties are strongly affected by the longitudinal weld seam,temperature, and loading direction. The room temperature(RT) deformation of welding zone is controlled by the dislocation slips with the association of some twins, while twinning plays significant roles in the accommodation of c-axis strain of the coarse grains on matrix zone.The deformation at RT stretched along extrusion direction(ED) and transverse direction(TD) are controlled by basal slip/twinning and basal slip/prismatic slip/twinning, respectively. During high temperature tension, the dislocation cross slip of pyramidal slip is activated, and grain boundary sliding occurred in welding zone, leading to the superplastic behavior. With the increase of tensile temperature, the predominant DRX mode is transformed from continuous DRX to discontinuous DRX. Moreover, the basal poles of the grains spread from TD towards ED with the decrease of maximum pole intensity when stretched along ED, while non-basal textures are transformed to (10-10) fiber texture when stretched along TD. The slip-dominated flow is seen during RT tension along ED, while twinning becomes predominant during RT tension along TD. The fine grain structure causes the superior RT tensile properties along ED of welding zone with ultimate tensile strength of 315 MPa and elongation to failure of 13.8%. With the increase of tensile temperature, the slipping-dominated deformation is transformed into twinning-dominated, causing the decrease of strength and increase of elongation.
基金the National Natural Science Foundation of China(51875317)Key Research and Development Program of Shandong Province(2019GGX104087)Natural Science Foundation of Shandong Province(ZR2019QEE030).
文摘Al/Mg/Al sheet with good bonding quality and mechanical properties was fabricated based on the proposed porthole die co-extrusion and forging(PCE-F)process.There were no voids,cracks or other defects on the Al/Mg interface.A continuous diffusion zone with two-sub-layer structure was formed across the Al/Mg interface,and its width increased with higher temperature or reduction ratio.The sub-layers formed at low and high temperature were identified to be solid solutions and intermetallic compounds(IMCs)including y-MgpAl^and^-Al3Mg.In Al layer,the welding zone mainly consisted of fine equiaxed grains with several coarse elongated grains,while the majority of matrix zone is coarse elongated grains.The rolling textures were dominated in both welding and matrix zones.In Mg layer,the welding zone exhibited complete DRXed grain structure,while several unDRXed coarse grains were observed in the matrix zone.With the increasing temperature,the grain size of Al and Mg layer firstly decreased and then increased.High reduction ratio strongly refined the grain structure of Al layer,while slightly affected the Mg layer.The Al/Mg/AI sheet experienced stress-drops twice during the tensile test.The first stress-drop was determined by the IMCs and microstructure of Mg layer,while the second stress-drop was closely related to the microstructure of Al layer.Al/Mg/Al sheet forged at the lowest temperature without the formation IMCs exhibited the highest stress for the first stress-drop,and that forged under the highest reduction ratio with the smallest grain size in Al layer had the highest stress for the second stress-drop.
基金financial support from National Natural Science Foundation of China(51875317)Key Research and Development Program of Shandong Province(2019GGX104087)National Natural Science Foundation of Shandong Province(ZR2019QEE030)
文摘The microstructure evolution of Mg-5.65 Zn-0.66 Zr(wt.%)alloy was studied based on the hot compression tests.The results indicated that the flow stress increased rapidly to a peak point at the initial stage,and then it gradually decreased.Moreover,high temperature and low strain rate resulted in the decreasing of flow stress.All samples exhibited a necklace grain structure because of the occurrence of partial dynamic recrystallization(DRX).High temperature increased both the size and fraction of DRXed grains,while high strain rate showed an opposite tendency.At the conditions of 350°C/0.001 s^(-1)and 350°C/0.1 s^(-1),the twins were not exhibited and DRX played a dominant role.Importantly,the obvious split of basal texture was observed.The pyramidal<c+a>slip with high value of Schmid factor was active in large deformed grains,which corresponded to the peak split point in(0001)pole figure.A mechanism about the grain rotation was proposed to explain the relationship between the pyramidal slip and the split of basal texture.Finally,it was found that large number of{10–12}extension twins were formed during the initial stage at condition of 300°C/1 s^(-1),and the number of twins decreased with the increase of strain.The twins greatly contributed to the fast formation of basal texture and grain rotation.Moreover,the non-basal slips were active in twining region,which could facilitate the nucleation of DRX.
基金support from the National Natural Science Foundation of China(Nos.51875317,52222510)the Key Research and Development Program of Shandong Province(No.2021ZLGX01).
文摘Abnormal grain growth(AGG)easily takes place in Mg alloys during high-temperature solutions,result-ing in deterioration of mechanical properties.Hence,the compression prior to solution(pre-compression)was conducted to suppress AGG,and the microstructure evolution as well as suppressing mechanisms was investigated based on quasi-in-situ analysis.After compression along the transverse direction,<11-20>//ED grains preferentially nucleated and rapidly grew up,and the initial<10-10>//ED texture was weakened.Two grain growth modes of heat-induced and strain-induced grain boundary migrations were found.The former was attributed to the high interfacial energy of grain boundaries with large curvature.The latter consumed the adjacent grains with high storage energy,forming abnormal grains with irregular shapes.The compression with a reduction>6%could obviously suppress AGG.The suppressing effects were mainly attributed to weakening the size advantage of<11-20>//ED grains,increasing nucleation,reducing grain boundary character distribution,and redistributing storage energy distribution.After 12%compression along the transverse direction,30°misorientation of<11-20>//ED grains and high energy grain boundaries were reduced.The{10-12}tensile twins and{10-15}high index twins induced by com-pression increased the nucleation of static recrystallization.Beside,compression introduces high-density dislocations,which also contributed to suppressing AGG behavior during solution.
基金financially supported by the National Natural Science Foundation of China(Nos.51875317 and 52222510)the Key Research and Development Program of Shandong Province(No.2021ZLGX01).
文摘The pre-tension was induced to suppress the abnormal grain growth(AGG)of ZK60 Mg profile during solution treatment.The effects of pre-tension on the microstructure evolution and mechanical properties were studied,and the suppressing mechanism was discussed.If the pre-tension strain was larger than 10%,AGG during solution could be effectively inhibited,resulting in a sharp decrease in the grain size.The suppression effects were realized by restricting the orientation dependent of AGG and promoting static recrystallization.The pre-tension reset the distributions of stored energy and sizes of the grains with〈11–20〉and〈10–10〉orientations,and thus retarded the orientation dependent of AGG.Moreover,the pre-tension introduced a mass of dislocations,twins,and stacking faults,all of which promoted the occurrence of static recrystallization,and the grain structure was further refined.The pre-tension accelerated the precipitation kinetics during aging,resulting in fine and dense precipitates.With the increase of pre-tension strain,the strength of ZK60 Mg profile monotonically increased.
基金financially supported by the National Science Foundation of China(No.51735008)the Science Fund for Distinguished Young Scholars of Shandong Province(No.JQ201810)。
文摘In this paper,a comparative study on the spray deposited and as-cast 2195 alloy was carried out to reveal their microstructure evolutions and differences during the homogenization process.The dissolution of the secondary particles and the diffusion of solute were studied based on microstructure characterization and kinetics analysis.The precipitation behavior of Al3Zr dispersoids and its influence on recrystallization were investigated by using TEM and EBSD characterization.It was found that the large-size particles at triangular grain boundaries dissolve slower than the intragranular phases and other grain boundary phases.The required homogenization time depends on the dissolution processes of the large-size phases at grain boundaries.The size of grain boundary phases in the spray deposited alloy is much smaller than that in the as-cast alloy,so the homogenization time required for the spray deposited alloy is significantly shorter.Two-stage and ramp heating homogenization processes can promote the precipitation of Al3Zr dispersoids in the two alloys.In the spray deposited alloy,the dispersoids tend to precipitate at the positions of the T1 plates dissolved,which causes a non-uniform distribution and decreases the recrystallization resistance of the alloy.However,the distribution of the dispersoids in the as-cast alloy is more uniform after the homogenization,which brings a stronger inhibition on the recrystallization.According to the microstructural characterization and kinetics analysis results,it can be concluded that the homogenization with a slow ramp heating is suitable for the two 2195 alloys,and a shorter holding time can be used for spray deposited alloy,e.g.12 h at 500℃,while the holding time for the as-cast alloy is no less than 35 h at 500℃.
基金financially supported by the National Natural Science Foundation of China(No.51875317)the Development Program of Shandong Province(No.2019GGX104087)the National Natural Science Foundation of Shandong Province(No.ZR2019QEE030)。
文摘Porthole die extrusion of Mg alloys was studied by means of experimental and numerical studies. Results indicated that an inhomogeneous microstructure formed on the cross-section of the extruded profile. On the profile surface, abnormal coarse grains with an orientation of <11-20> in parallel to ED(extrusion direction) appeared. In the profile center, the welding zone was composed of fine grains with an average size of 4.19 um and an orientation of <10-10> in parallel to ED, while the matrix zone exhibited a bimodal grain structure. Disk-like, near-spherical and rod-like precipitates were observed, and the number density of those features was lower on the profile surface than that in the profile center. Then, the formation and evolution of coarse grains on the profile surface were investigated, which were found to depend on the competition between static recrystallization and grain growth. The stored deformation energy was the factor dominating the surface structure through effective regulation over nucleation of the precipitates and recrystallization. A profile with a low stored deformation energy suppressed formation of precipitates and consequently facilitated grain growth rather than recrystallization, resulting in the formation of abnormal coarse grains. Finally, the surface coarse grains contributed detrimentally to hardness, tensile properties, and wear performance of the bulk structure.
