The residual stress in a 20%SiC w/6061Al composite as extruded was investigated by using X ray stress measurement method. It was found that, high residual stress existed in the composite and residual stress distributi...The residual stress in a 20%SiC w/6061Al composite as extruded was investigated by using X ray stress measurement method. It was found that, high residual stress existed in the composite and residual stress distribution in each direction are not uniform. Relaxation process of residual stress in the composite was dynamically measured during annealing at high temperature. It is verified that the relaxation of residual stress obeys the power law at high temperature. With the creep mechanism, the relaxation behavior of residual stresses at high temperature was analyzed. The results show that, the stress exponent and activation energy for stress relaxation of the composite are obviously higher than those of the matrix alloy.展开更多
The application of compound parts of Al [AlBO] w/Al not only reduces the cost of the parts but also improves its properties. However, there is a large thermal residual stress between Al and [AlBO] w/Al, and it is harm...The application of compound parts of Al [AlBO] w/Al not only reduces the cost of the parts but also improves its properties. However, there is a large thermal residual stress between Al and [AlBO] w/Al, and it is harmful for practical application. From the theoretical analyses and experimental results, it was found that by the compressive pre plastic deformation perpendicular to the interface between Al and [AlBO] w/Al, the interlayer residual stress of compound parts can be reduced, while the mechanical properties of compound parts can be improved. [展开更多
With a micro mechanical model, the feasibility of modification of thermal residual stress of the composites treated by tensile pre plastic deformation was analyzed. The relationship between pre plastic strain and vari...With a micro mechanical model, the feasibility of modification of thermal residual stress of the composites treated by tensile pre plastic deformation was analyzed. The relationship between pre plastic strain and variation of thermal residual stress was established. By using the method of tensile pre plastic deformation, the thermal residual stress in 20%SiC w/6061Al composites was modified. The results show that, with increasing tensile pre plastic strain, the tensile residual stress in the matrix was decreased to zero gradually, and then it was turned into compressive stress. By comparison, it was found that the changing tendency of the test results is similar to that of theoretical analysis. In addition, due to pre plastic deformation, the dislocation density in the matrix was increased, and the yield strength of the composites was improved. The increasing yield strength is mainly due to the decreasing tensile residual stress and the changing of distribution of dislocation in the matrix.展开更多
Barley(Hordeum vulgare L.)is one of the most Aluminum(Al)sensitive cereal species.In this study,the physiological,biochemical,and molecular response of barley seedlings to Al treatment was examined to gain insight int...Barley(Hordeum vulgare L.)is one of the most Aluminum(Al)sensitive cereal species.In this study,the physiological,biochemical,and molecular response of barley seedlings to Al treatment was examined to gain insight into Al response and tolerance mechanisms.The results showed that superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)activity were inhibited to different degrees following Al exposure.The MDA content also significantly increased with increasing Al concentrations.SRAP results indicated significant differences between Al treatments and controls in terms of SRAP profile,and the genomic template stability(GTS)decreased with increasing Al concentration and duration.These integrative results help to elucidate the underlying mechanisms that the barley response to Al toxicity.展开更多
In order to improve the stress corrosion cracking resistance of the weldable Al Zn Mg alloys with medium strength, the near solvus pre precipitation following high temperature solution treatment was performed on LC52 ...In order to improve the stress corrosion cracking resistance of the weldable Al Zn Mg alloys with medium strength, the near solvus pre precipitation following high temperature solution treatment was performed on LC52 and 7039 aluminum alloys. The effect of the pre precipitation on the microstructure, age hardening and stress corrosion cracking of LC52 and 7039 alloy was investigated. The results show that the near solvus pre precipitation can be limited on grain boundary and can enhance the discontinuity of grain boundary precipitates. The stress corrosion cracking resistance of aged Al Zn Mg alloys can be improved with non deteriorated strength and plasticity via pre precipitation.展开更多
The effect of stress on the microstructure and properties of an Al-Cu-Mg-Ag alloy under-aged at 165 ℃ for 2 h during thermal exposure at 200 ℃ was investigated. The tensile experimental results show that the remaine...The effect of stress on the microstructure and properties of an Al-Cu-Mg-Ag alloy under-aged at 165 ℃ for 2 h during thermal exposure at 200 ℃ was investigated. The tensile experimental results show that the remained tensile strength of both specimens at room temperature after being exposed at 200 ℃ with and without applying stress rises firstly, and then drops with the increasing of exposure time. The peak value of the remained strength reaches 439 MPa for non-stress-exposure for 10 h, and 454 MPa after being exposed with stress loaded for 20 h at 220 MPa. The elongation change is similar to that of strength. After being exposed for 100 h, specimen exposed at 220 MPa still remains a tensile strength of 401 MPa, larger than that exposed without applying stress. TEM shows that the microstructure of under-aged alloy is dominated by - phase mainly and a little θ′ phase. The θ′ and - phases are believed competitive with increasing exposure time. The width of precipitation free zone(PFZ) increases and the granular second phase precipitates at grain-boundary correspondingly. It is shown that the mechanical properties of alloy decrease slightly and present good thermal stability after thermal exposure at 200 ℃ and 220 MPa for 100 h.展开更多
Studies were made of the influence of aging conditions and applied potentials on the stress corrosion carcking(SCC)susceptibility for an Al-Li-Cu-Mg alloy by slow strain rate technique.The relationship between the rel...Studies were made of the influence of aging conditions and applied potentials on the stress corrosion carcking(SCC)susceptibility for an Al-Li-Cu-Mg alloy by slow strain rate technique.The relationship between the relative hydrogen content on specimen surface,the applied potentials and elapsed time has also been examined.The SCC susceptibility was found to be dependent on aging conditions in which the peak aged condition gave the worst SCC resistance and the natural aged condition had the best one. The SCC susceptibility and surface hydrogen content relates to the applied potentials. The anodic potentials increase SCC susceptibility,while the cathodic ones below the critical potential accelerate SCC.It is considered that both the anodic dissolution and展开更多
The hot deformation behavior of Al-Cu-Mg-Ag was studied by isothermal hot compression tests in the temperature range of 573-773 K and strain rate range of 0.001-1 s^-1 on a Gleeble 1500 D thermal mechanical simulator....The hot deformation behavior of Al-Cu-Mg-Ag was studied by isothermal hot compression tests in the temperature range of 573-773 K and strain rate range of 0.001-1 s^-1 on a Gleeble 1500 D thermal mechanical simulator. The results show the flow stress of Al-Cu-Mg-Ag alloy increases with strain rate and decreases after a peak value, indicating dynamic recovery and recrystallization. A hyperbolic sine relationship is found to correlate well the flow stress with the strain rate and temperature, the flow stress equation is estimated to illustrate the relation of strain rate and stress and temperature during high temperature deformation process. The processing maps exhibit two domains as optimum fields for hot deformation at different strains, including the high strain rate domain in 623-773 K and the low strain rate domain in 573-673 K.展开更多
In order to improve the stress corrosion cracking(SCC) resistance of 7A05Al alloy, four different heat treatment processes were performed. After the heat treatments, the stress corrosion cracking resistance, mechanica...In order to improve the stress corrosion cracking(SCC) resistance of 7A05Al alloy, four different heat treatment processes were performed. After the heat treatments, the stress corrosion cracking resistance, mechanical properties and microstructures of 7A05A1 alloys were studied. The results show that the retrogression and reaging(RRA) treated specimens possess the highest SCC resistance with slightly reduced strength compared with the other specimens. Thus RRA is the best process in terms of the optimal combination of SCC resistance and strength. Further TEM observation reveals that the RRA treated specimens are characterized by the fine equiaxed grains, dispersed second phase and wide PFZ. The pre-aging treated specimens show lower SCC resistance but higher strength as compared with the RRA treated ones. Equiaxed grains are also observed in the pre-aging treated samples by TEM, indicating that the anisotropy is eliminated. However, the dual aging and deformation plus aging treated specimens are demonstrated by large anisotropy.展开更多
The corrosion behaviors of 1420 and 2195 Al-Li alloys under 308 and 490 MPa tensile stress respectively in neutral 3.5% NaCl solution were investigated using electrochemical impedance spectroscopy(EIS) and scanning el...The corrosion behaviors of 1420 and 2195 Al-Li alloys under 308 and 490 MPa tensile stress respectively in neutral 3.5% NaCl solution were investigated using electrochemical impedance spectroscopy(EIS) and scanning electron microscope(SEM). It is found that the unstressed 1420 alloy is featured with large and discrete pits, while general corrosion and localized corrosion including intergranular corrosion and pitting corrosion occur on the unstressed 2195 alloy. As stress is applied to 1420 alloy, the pit becomes denser and its size is decreased. While, for the stressed 2195 alloy, intergranular corrosion is greatly aggravated and severe general corrosion is developed from connected pits. The EIS analysis shows that more severe general corrosion and localized corrosion occur on the stressed 2195 Al-Li alloy than on 1420 Al-Li alloy. It is suggested that tensile stress has greater effect on the corrosion of 2195 Al-Li alloy than on 1420 Al-Li alloy.展开更多
A notch sensitivity factor was derived in order to evaluate the stress concentration sensitivity of Al Li based alloys. The factor values for the Al Li alloy sheets containing various contents of impurities and ceri...A notch sensitivity factor was derived in order to evaluate the stress concentration sensitivity of Al Li based alloys. The factor values for the Al Li alloy sheets containing various contents of impurities and cerium addition were evaluated by determining the mechanical properties. It is found that the impurities Fe, Si, Na and K significantly enhance the stress concentration sensitivity of the alloys 2090 and 8090, whereas cerium addition reduces the stress concentration sensitivity to a certain degree for the high strength alloys. However, an excess amount of cerium addition in the high ductility alloy 1420 can significantly increase the stress concentration sensitivity. As compared with conventional aluminum alloys, the Al Li based alloys generally show high stress concentration sensitivity. Therefore, a special attention must be paid to this problem in the practical application of Al Li based alloys.展开更多
文摘The residual stress in a 20%SiC w/6061Al composite as extruded was investigated by using X ray stress measurement method. It was found that, high residual stress existed in the composite and residual stress distribution in each direction are not uniform. Relaxation process of residual stress in the composite was dynamically measured during annealing at high temperature. It is verified that the relaxation of residual stress obeys the power law at high temperature. With the creep mechanism, the relaxation behavior of residual stresses at high temperature was analyzed. The results show that, the stress exponent and activation energy for stress relaxation of the composite are obviously higher than those of the matrix alloy.
文摘The application of compound parts of Al [AlBO] w/Al not only reduces the cost of the parts but also improves its properties. However, there is a large thermal residual stress between Al and [AlBO] w/Al, and it is harmful for practical application. From the theoretical analyses and experimental results, it was found that by the compressive pre plastic deformation perpendicular to the interface between Al and [AlBO] w/Al, the interlayer residual stress of compound parts can be reduced, while the mechanical properties of compound parts can be improved. [
文摘With a micro mechanical model, the feasibility of modification of thermal residual stress of the composites treated by tensile pre plastic deformation was analyzed. The relationship between pre plastic strain and variation of thermal residual stress was established. By using the method of tensile pre plastic deformation, the thermal residual stress in 20%SiC w/6061Al composites was modified. The results show that, with increasing tensile pre plastic strain, the tensile residual stress in the matrix was decreased to zero gradually, and then it was turned into compressive stress. By comparison, it was found that the changing tendency of the test results is similar to that of theoretical analysis. In addition, due to pre plastic deformation, the dislocation density in the matrix was increased, and the yield strength of the composites was improved. The increasing yield strength is mainly due to the decreasing tensile residual stress and the changing of distribution of dislocation in the matrix.
基金Projects(U22A20190, 52175373, 52005516) supported by the National Natural Science Foundation of ChinaProject(ZZYJKT2021-03) supported by the State Key Laboratory of High Performance Complex Manufacturing,Central South University,ChinaProject(2020RC4001) supported by the Science and Technology Innovation Program of Hunan Province,China。
基金This research was funded by National Key Technology Research and Development Program(2015BAD01B02)the National Natural Science Foundation of China(31401316).
文摘Barley(Hordeum vulgare L.)is one of the most Aluminum(Al)sensitive cereal species.In this study,the physiological,biochemical,and molecular response of barley seedlings to Al treatment was examined to gain insight into Al response and tolerance mechanisms.The results showed that superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)activity were inhibited to different degrees following Al exposure.The MDA content also significantly increased with increasing Al concentrations.SRAP results indicated significant differences between Al treatments and controls in terms of SRAP profile,and the genomic template stability(GTS)decreased with increasing Al concentration and duration.These integrative results help to elucidate the underlying mechanisms that the barley response to Al toxicity.
基金the National Key R&D Program of China(No.2018YFA0707300)the National Natural Science Foundation of China(Nos.51904206,52105390,51905372,51805359)+3 种基金the China Postdoctoral Science Foundation(No.2020M670705)the Natural Science Foundation of Shanxi Province,China(No.201801D221130)the Major Program of National Natural Science Foundation of China(No.U1710254)the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi Province,China(No.2019L0258).
文摘In order to improve the stress corrosion cracking resistance of the weldable Al Zn Mg alloys with medium strength, the near solvus pre precipitation following high temperature solution treatment was performed on LC52 and 7039 aluminum alloys. The effect of the pre precipitation on the microstructure, age hardening and stress corrosion cracking of LC52 and 7039 alloy was investigated. The results show that the near solvus pre precipitation can be limited on grain boundary and can enhance the discontinuity of grain boundary precipitates. The stress corrosion cracking resistance of aged Al Zn Mg alloys can be improved with non deteriorated strength and plasticity via pre precipitation.
基金Project(2005CB623705-04) supported by the National Basic Research Program of China
文摘The effect of stress on the microstructure and properties of an Al-Cu-Mg-Ag alloy under-aged at 165 ℃ for 2 h during thermal exposure at 200 ℃ was investigated. The tensile experimental results show that the remained tensile strength of both specimens at room temperature after being exposed at 200 ℃ with and without applying stress rises firstly, and then drops with the increasing of exposure time. The peak value of the remained strength reaches 439 MPa for non-stress-exposure for 10 h, and 454 MPa after being exposed with stress loaded for 20 h at 220 MPa. The elongation change is similar to that of strength. After being exposed for 100 h, specimen exposed at 220 MPa still remains a tensile strength of 401 MPa, larger than that exposed without applying stress. TEM shows that the microstructure of under-aged alloy is dominated by - phase mainly and a little θ′ phase. The θ′ and - phases are believed competitive with increasing exposure time. The width of precipitation free zone(PFZ) increases and the granular second phase precipitates at grain-boundary correspondingly. It is shown that the mechanical properties of alloy decrease slightly and present good thermal stability after thermal exposure at 200 ℃ and 220 MPa for 100 h.
文摘Studies were made of the influence of aging conditions and applied potentials on the stress corrosion carcking(SCC)susceptibility for an Al-Li-Cu-Mg alloy by slow strain rate technique.The relationship between the relative hydrogen content on specimen surface,the applied potentials and elapsed time has also been examined.The SCC susceptibility was found to be dependent on aging conditions in which the peak aged condition gave the worst SCC resistance and the natural aged condition had the best one. The SCC susceptibility and surface hydrogen content relates to the applied potentials. The anodic potentials increase SCC susceptibility,while the cathodic ones below the critical potential accelerate SCC.It is considered that both the anodic dissolution and
基金the National Basic Research Program of China(No.2005CB623705)
文摘The hot deformation behavior of Al-Cu-Mg-Ag was studied by isothermal hot compression tests in the temperature range of 573-773 K and strain rate range of 0.001-1 s^-1 on a Gleeble 1500 D thermal mechanical simulator. The results show the flow stress of Al-Cu-Mg-Ag alloy increases with strain rate and decreases after a peak value, indicating dynamic recovery and recrystallization. A hyperbolic sine relationship is found to correlate well the flow stress with the strain rate and temperature, the flow stress equation is estimated to illustrate the relation of strain rate and stress and temperature during high temperature deformation process. The processing maps exhibit two domains as optimum fields for hot deformation at different strains, including the high strain rate domain in 623-773 K and the low strain rate domain in 573-673 K.
基金Project(Z172003A001) supported by the Ministerial Level Research Foundation
文摘In order to improve the stress corrosion cracking(SCC) resistance of 7A05Al alloy, four different heat treatment processes were performed. After the heat treatments, the stress corrosion cracking resistance, mechanical properties and microstructures of 7A05A1 alloys were studied. The results show that the retrogression and reaging(RRA) treated specimens possess the highest SCC resistance with slightly reduced strength compared with the other specimens. Thus RRA is the best process in terms of the optimal combination of SCC resistance and strength. Further TEM observation reveals that the RRA treated specimens are characterized by the fine equiaxed grains, dispersed second phase and wide PFZ. The pre-aging treated specimens show lower SCC resistance but higher strength as compared with the RRA treated ones. Equiaxed grains are also observed in the pre-aging treated samples by TEM, indicating that the anisotropy is eliminated. However, the dual aging and deformation plus aging treated specimens are demonstrated by large anisotropy.
基金Project(50401012) supported by the National Natural Science Foundation of China
文摘The corrosion behaviors of 1420 and 2195 Al-Li alloys under 308 and 490 MPa tensile stress respectively in neutral 3.5% NaCl solution were investigated using electrochemical impedance spectroscopy(EIS) and scanning electron microscope(SEM). It is found that the unstressed 1420 alloy is featured with large and discrete pits, while general corrosion and localized corrosion including intergranular corrosion and pitting corrosion occur on the unstressed 2195 alloy. As stress is applied to 1420 alloy, the pit becomes denser and its size is decreased. While, for the stressed 2195 alloy, intergranular corrosion is greatly aggravated and severe general corrosion is developed from connected pits. The EIS analysis shows that more severe general corrosion and localized corrosion occur on the stressed 2195 Al-Li alloy than on 1420 Al-Li alloy. It is suggested that tensile stress has greater effect on the corrosion of 2195 Al-Li alloy than on 1420 Al-Li alloy.
文摘A notch sensitivity factor was derived in order to evaluate the stress concentration sensitivity of Al Li based alloys. The factor values for the Al Li alloy sheets containing various contents of impurities and cerium addition were evaluated by determining the mechanical properties. It is found that the impurities Fe, Si, Na and K significantly enhance the stress concentration sensitivity of the alloys 2090 and 8090, whereas cerium addition reduces the stress concentration sensitivity to a certain degree for the high strength alloys. However, an excess amount of cerium addition in the high ductility alloy 1420 can significantly increase the stress concentration sensitivity. As compared with conventional aluminum alloys, the Al Li based alloys generally show high stress concentration sensitivity. Therefore, a special attention must be paid to this problem in the practical application of Al Li based alloys.
