The effect of Li(2.0 wt%)addition on mechanical properties and ageing precipitation behavior of Al-3.0 Mg 0.5 Si was investigated by tensile test,dynamic elasticity modulus test,scanning electron microscopy(SEM),trans...The effect of Li(2.0 wt%)addition on mechanical properties and ageing precipitation behavior of Al-3.0 Mg 0.5 Si was investigated by tensile test,dynamic elasticity modulus test,scanning electron microscopy(SEM),transmission electron microscopy(TEM)and high-resolution transmission electron microscopy(HRTEM)images.The results show that the tensile strength of the Li-containing alloy can be significantly improved;however,the ductility is sharply decreased and the fracture mechanism changes from ductile fracture to intergranular fracture.The elasticity modulus of the Li-containing alloy increases by 11.6%compared with the base alloy.The microstructure observation shows that the Li addition can absolutely change the precipitation behavior of the base alloy,andδ′-Al_(3)Li phase becomes the main precipitates.Besides,β′′-Mg_(2)Si andδ′-Al_(3)Li dual phases precipitation can be visibly observed at 170℃ ageing for 100 h,although the quantity ofδ′-Al_(3)Li phase is more thanβ′′-Mg_(2)Si phase.The width of the precipitate-free zone(PFZ)of the Li-containing alloy is much wider at the over-ageing state than the base alloy,which has a negative impact on the ductile and results in the decrease of elongation.展开更多
The effects of heat treatment on microstructures and hardening response of Mg-6Zn4）.5Er4）.5Ca （wt%） alloy were investigated by optical microscope （OM）, scanning elec- tron microscope （SEM）, and transmission el...The effects of heat treatment on microstructures and hardening response of Mg-6Zn4）.5Er4）.5Ca （wt%） alloy were investigated by optical microscope （OM）, scanning elec- tron microscope （SEM）, and transmission electron microscope （TEM） in this paper. The results show that the Mg（Zn4）.5Er- 0.5Ca alloy contains Mg3Zn6Erx quasicrystalline phase （I- phase） and Ca2Mg6Zn3 phase under as-cast condition. Most of the Ca2Mg6Zn3 phases and I-phases dissolve into matrix during heat treatment at 475 ℃ for 5 h. After the as-solution alloy was aged at 175 ℃ for 36 h, a large amount of MgZn2 precipitate with several nanometers precipitate. It is suggested that the trace addition of Ca results in refining the size of the precipitate, and the presence of the nanoscale MgZn2 phase is the main factor to improve the peak-aged hardness greatly to 87 HV, which in- creases about 40 % compared with that of as-cast alloy.展开更多
Magnesium-gadolinium(Mg-Gd)-based alloys have excellent high-temperature properties and the addition of two heterogeneous rare earth(RE)elements may promote the formation of secondary phase for better-strengthened pro...Magnesium-gadolinium(Mg-Gd)-based alloys have excellent high-temperature properties and the addition of two heterogeneous rare earth(RE)elements may promote the formation of secondary phase for better-strengthened properties.Herein,novel Mg-7Gd-2Nd-0.5Zr(wt%)alloys were prepared by synergistic reaction induced by high-speed extrusion(EX)and short-time aging treatment(AT).The microstructures,textures,and mechanical properties of the resulting alloys were then comprehensively studied by various analytical methods.The result reveals that the as-cast Mg-7Gd-2Nd-0.5Zr(wt%)alloy is composed of a-Mg matrix and Mg5(Gd,Nd)phase with bony and continuous networks at grain boundaries.The microstructure presents coarse deformed grains and fine recrystallized grains after high-speed EX,and formation of typical(0001)||ED extruded fiber texture and[1211]RE texture is observed.The EX22 sample exhibits more Mg5(Gd,Nd)precipitated phases,fuller DRXed grains,and shorter peak aging times than the EX9 sample.After the AT at 250℃,the proportion of deformed grains decreases due to static recrystallization,which leads to a reduction in the average grain size and weakening of the texture intensity.Therefore,combined effect of all strengthening mechanisms aids in achieving balance of high-strength and high-elongation for Mg-7Gd-2Nd-0.5Zr(wt%)alloy.The values of yield strength(YS),ultimate tensile strength(UTS),and elongation(EL)of EX22-A sample at room temperature are found to be 292.5 MPa,350.6 MPa,and 24.3%,respectively.Overall,this study provides relevant experimental basis and theoretical guidance for the development of high-strength Mg-RE alloys,which are useful for future consideration.展开更多
基金Project(2016YFB0300802)supported by the National Key Research and Development Program of China。
文摘The effect of Li(2.0 wt%)addition on mechanical properties and ageing precipitation behavior of Al-3.0 Mg 0.5 Si was investigated by tensile test,dynamic elasticity modulus test,scanning electron microscopy(SEM),transmission electron microscopy(TEM)and high-resolution transmission electron microscopy(HRTEM)images.The results show that the tensile strength of the Li-containing alloy can be significantly improved;however,the ductility is sharply decreased and the fracture mechanism changes from ductile fracture to intergranular fracture.The elasticity modulus of the Li-containing alloy increases by 11.6%compared with the base alloy.The microstructure observation shows that the Li addition can absolutely change the precipitation behavior of the base alloy,andδ′-Al_(3)Li phase becomes the main precipitates.Besides,β′′-Mg_(2)Si andδ′-Al_(3)Li dual phases precipitation can be visibly observed at 170℃ ageing for 100 h,although the quantity ofδ′-Al_(3)Li phase is more thanβ′′-Mg_(2)Si phase.The width of the precipitate-free zone(PFZ)of the Li-containing alloy is much wider at the over-ageing state than the base alloy,which has a negative impact on the ductile and results in the decrease of elongation.
基金financial supported by the National Natural Science Foundation of China(No.51301006)the Projects of Beijing Municipal Science and Technology Commission(No.Z131100003213019)+1 种基金the Projects of Beijing Municipal Commission of Education(Nos.KM201310005001 and KM201410005014)Beijing Natural Science Foundation(No.2142005)
文摘The effects of heat treatment on microstructures and hardening response of Mg-6Zn4）.5Er4）.5Ca （wt%） alloy were investigated by optical microscope （OM）, scanning elec- tron microscope （SEM）, and transmission electron microscope （TEM） in this paper. The results show that the Mg（Zn4）.5Er- 0.5Ca alloy contains Mg3Zn6Erx quasicrystalline phase （I- phase） and Ca2Mg6Zn3 phase under as-cast condition. Most of the Ca2Mg6Zn3 phases and I-phases dissolve into matrix during heat treatment at 475 ℃ for 5 h. After the as-solution alloy was aged at 175 ℃ for 36 h, a large amount of MgZn2 precipitate with several nanometers precipitate. It is suggested that the trace addition of Ca results in refining the size of the precipitate, and the presence of the nanoscale MgZn2 phase is the main factor to improve the peak-aged hardness greatly to 87 HV, which in- creases about 40 % compared with that of as-cast alloy.
基金Project supported by the Natural Science Foundation of Shanxi Province(20210302123135,202303021221143)Scientific and Technological Achievements Transformation Guidance Special Project of Shanxi Province(202104021301022,202204021301009)+1 种基金Central Government Guided Local Science and Technology Development Projects(YDZJSX20231B003,YDZJSX2021A010)National Natural Science Foundation of China(52374395)。
文摘Magnesium-gadolinium(Mg-Gd)-based alloys have excellent high-temperature properties and the addition of two heterogeneous rare earth(RE)elements may promote the formation of secondary phase for better-strengthened properties.Herein,novel Mg-7Gd-2Nd-0.5Zr(wt%)alloys were prepared by synergistic reaction induced by high-speed extrusion(EX)and short-time aging treatment(AT).The microstructures,textures,and mechanical properties of the resulting alloys were then comprehensively studied by various analytical methods.The result reveals that the as-cast Mg-7Gd-2Nd-0.5Zr(wt%)alloy is composed of a-Mg matrix and Mg5(Gd,Nd)phase with bony and continuous networks at grain boundaries.The microstructure presents coarse deformed grains and fine recrystallized grains after high-speed EX,and formation of typical(0001)||ED extruded fiber texture and[1211]RE texture is observed.The EX22 sample exhibits more Mg5(Gd,Nd)precipitated phases,fuller DRXed grains,and shorter peak aging times than the EX9 sample.After the AT at 250℃,the proportion of deformed grains decreases due to static recrystallization,which leads to a reduction in the average grain size and weakening of the texture intensity.Therefore,combined effect of all strengthening mechanisms aids in achieving balance of high-strength and high-elongation for Mg-7Gd-2Nd-0.5Zr(wt%)alloy.The values of yield strength(YS),ultimate tensile strength(UTS),and elongation(EL)of EX22-A sample at room temperature are found to be 292.5 MPa,350.6 MPa,and 24.3%,respectively.Overall,this study provides relevant experimental basis and theoretical guidance for the development of high-strength Mg-RE alloys,which are useful for future consideration.
