Although magnesium(Mg)alloys are the lightest among structural metals,their inadequate corrosion resistance makes them difficult to be used in energy-saving lightweight structures.Moreover,the improvement in corrosion...Although magnesium(Mg)alloys are the lightest among structural metals,their inadequate corrosion resistance makes them difficult to be used in energy-saving lightweight structures.Moreover,the improvement in corrosion resistance by the conventional surface treatments is always achieved at the expense of sacrificing the fatigue lifetime.In this study,high purity aluminum(Al)and AlMgSi alloy coatings were deposited on Mg alloys via an in-situ micro-forging(MF)assisted cold spray(MFCS)process for simultaneous higher corrosion resistance and longer fatigue lifetime.Besides contributing to a highly dense microstructure,the in-situ MF also greatly refines the grain of the deposited Al alloy coating to the sub-micrometer range due to the enhanced dynamic recrystallization and also generates notable compressive residual stress up to 210 MPa within the AlMgSi coating.The absence of secondary phases in the AlMgSi alloy coatings enable the coated Mg alloy with corrosion resistance,which is even better than its bulk AlMgSi counterparts.The unique combination of refined microstructure and the prominent compressive residual stress within the AlMgSi coatings,effectively delayed the crack initiation upon repeated dynamic loading,thereby leading to∼10 times increase in the fatigue lifetime of the Mg Alloy.However,although residual stress is also generated in the submmicro-sized grained pure Al coating,the low intrinsic strength of the coating layer leads to a lower fatigue lifetime than the uncoated Mg alloy substrate.The present work is aimed to provide a facile approach to break the trade-off between corrosion resistance improvement and fatigue lifetime of the coated Mg alloys.展开更多
The effects of 2%Ca addition on the microstructure and the mechanical properties of the asymmetric double-sided friction stir welded magnesium alloy AZ61 were investigated.Compared to the Ca-free AZ61magnesium alloy,t...The effects of 2%Ca addition on the microstructure and the mechanical properties of the asymmetric double-sided friction stir welded magnesium alloy AZ61 were investigated.Compared to the Ca-free AZ61magnesium alloy,the addition of 2%Ca significantly refines the grains in the stir zone after welding.Due to the existence of thermally stable Al2Ca particles,there is no noticeable change in the grain size in the stir zone regardless of the welding heat input.The electron backscattered diffraction analysis at the center of the stir zone confirmed the significant deterioration of the(0001)texture strength from the addition of 2%Ca.The tensile test of the joint suggested that the addition of 2%Ca provides stable tensile properties to the joint regardless of the welding parameters.The critical(0001)texture strength that determines the ultimate tensile strength decreased from 20 to 15 by the Ca addition.The addition of Ca enhanced the deterioration of the plastic elongation when the(0001)texture strength increased.展开更多
In this study, the effect of the processing route using a friction stir processing(FSP) method on the microstructure and mechanical behavior of a Mg-9Li-1Zn alloy was systematically investigated. In the FSP method, th...In this study, the effect of the processing route using a friction stir processing(FSP) method on the microstructure and mechanical behavior of a Mg-9Li-1Zn alloy was systematically investigated. In the FSP method, the odd-numbered(1st and 3rd) process directions and even-numbered(2nd and 4th) passes were alternated to distribute the strain throughout the whole processed zone uniformly. Consequently, the processed zone had a much more uniform microstructure and hardness distribution than the processed zone obtained using the conventional FSP method. Using this method, the grain size of a Mg-9Li-1Zn sheet alloy was refined from ~31 μm to ~0.21 μm with uniformly distributedα and β phases. The processed alloy exhibited a high strength-ductility synergy with an ultimate tensile strength(UTS) of 220.1 MPa and total elongation of 70.0% at a strain rate of 10^(-3)s^(-1), overwhelmingly higher than those of the base metal, 155.6 MPa in UTS and 36.0%in elongation. The in-situ SEM-DIC analysis and TEM observation demonstrated that such an outstanding ductility with moderate strength is caused by grain boundary sliding, the dominant deformation mechanism of the ultra-fine-grained sample after FSP. The processing route with reverse processing direction was proven to be efficient in producing the ultrafine grain size microstructure and improving the mechanical properties of superlight Mg-9Li-1Zn alloy.展开更多
基金supported by the National Natural Science Foundation of China(51875443)Guangdong Basic and Applied Basic Research Foundation(2019B1515120016,202002030290).
文摘Although magnesium(Mg)alloys are the lightest among structural metals,their inadequate corrosion resistance makes them difficult to be used in energy-saving lightweight structures.Moreover,the improvement in corrosion resistance by the conventional surface treatments is always achieved at the expense of sacrificing the fatigue lifetime.In this study,high purity aluminum(Al)and AlMgSi alloy coatings were deposited on Mg alloys via an in-situ micro-forging(MF)assisted cold spray(MFCS)process for simultaneous higher corrosion resistance and longer fatigue lifetime.Besides contributing to a highly dense microstructure,the in-situ MF also greatly refines the grain of the deposited Al alloy coating to the sub-micrometer range due to the enhanced dynamic recrystallization and also generates notable compressive residual stress up to 210 MPa within the AlMgSi coating.The absence of secondary phases in the AlMgSi alloy coatings enable the coated Mg alloy with corrosion resistance,which is even better than its bulk AlMgSi counterparts.The unique combination of refined microstructure and the prominent compressive residual stress within the AlMgSi coatings,effectively delayed the crack initiation upon repeated dynamic loading,thereby leading to∼10 times increase in the fatigue lifetime of the Mg Alloy.However,although residual stress is also generated in the submmicro-sized grained pure Al coating,the low intrinsic strength of the coating layer leads to a lower fatigue lifetime than the uncoated Mg alloy substrate.The present work is aimed to provide a facile approach to break the trade-off between corrosion resistance improvement and fatigue lifetime of the coated Mg alloys.
基金This study was partially supported by the New Energy and Industrial Technology Development Organization(NEDO)under the“Innovation Structural Materials Project(Future Pioneering Projects)”.
文摘The effects of 2%Ca addition on the microstructure and the mechanical properties of the asymmetric double-sided friction stir welded magnesium alloy AZ61 were investigated.Compared to the Ca-free AZ61magnesium alloy,the addition of 2%Ca significantly refines the grains in the stir zone after welding.Due to the existence of thermally stable Al2Ca particles,there is no noticeable change in the grain size in the stir zone regardless of the welding heat input.The electron backscattered diffraction analysis at the center of the stir zone confirmed the significant deterioration of the(0001)texture strength from the addition of 2%Ca.The tensile test of the joint suggested that the addition of 2%Ca provides stable tensile properties to the joint regardless of the welding parameters.The critical(0001)texture strength that determines the ultimate tensile strength decreased from 20 to 15 by the Ca addition.The addition of Ca enhanced the deterioration of the plastic elongation when the(0001)texture strength increased.
基金partially supported by the JST-Mirai Program Grant Number JPMJMI19E5a Grant-in-Aid for Science Research from the Japan Society for the Promotion of Science。
文摘In this study, the effect of the processing route using a friction stir processing(FSP) method on the microstructure and mechanical behavior of a Mg-9Li-1Zn alloy was systematically investigated. In the FSP method, the odd-numbered(1st and 3rd) process directions and even-numbered(2nd and 4th) passes were alternated to distribute the strain throughout the whole processed zone uniformly. Consequently, the processed zone had a much more uniform microstructure and hardness distribution than the processed zone obtained using the conventional FSP method. Using this method, the grain size of a Mg-9Li-1Zn sheet alloy was refined from ~31 μm to ~0.21 μm with uniformly distributedα and β phases. The processed alloy exhibited a high strength-ductility synergy with an ultimate tensile strength(UTS) of 220.1 MPa and total elongation of 70.0% at a strain rate of 10^(-3)s^(-1), overwhelmingly higher than those of the base metal, 155.6 MPa in UTS and 36.0%in elongation. The in-situ SEM-DIC analysis and TEM observation demonstrated that such an outstanding ductility with moderate strength is caused by grain boundary sliding, the dominant deformation mechanism of the ultra-fine-grained sample after FSP. The processing route with reverse processing direction was proven to be efficient in producing the ultrafine grain size microstructure and improving the mechanical properties of superlight Mg-9Li-1Zn alloy.
