Mg-7Gd-5Y-1Nd-xZn-0.5Zr(x=0,1,2)挤压态合金微观组织和力学性能

采用扫描电子显微镜、电子背散射衍射、透射电子显微镜、高角度环形暗场?扫描透射,分析了Mg-7Gd-5Y-1Nd-xZn-0.5Zr(x=0,1,2,质量分数,%)挤压态合金微观组织结构和力学性能,旨在探索Zn对于合金性能影响的微观机制。结果表明:在Mg-7Gd-5Y-1Nd-0.5Zr合金中添加Zn元素,不仅形成LPSO结构,也促进了Mg5(RE,Zn)颗粒的析出,并与Zr形成Zn-Zr相。LPSO结构不仅能阻碍晶粒长大,细化晶粒;也能够阻碍动态再结晶,从而形成动态再结晶晶粒和变形晶粒共存的双模结构,动态再结晶晶粒为á0001?//ED织构,变形晶粒为á1010?//ED织构。微米级大尺寸Mg5(RE,Zn)颗粒会导致应力集中,引起裂纹的萌生,降低合金的塑性;均匀分布的亚微米级Mg5(RE,Zn)颗粒起第二相强化作用,并能钉扎晶界,阻碍晶粒长大。对比3种挤压态合金,Mg-7Gd-5Y-1Nd-2Zn-0.5Zr合金获得了最优的力学性能,其抗拉强度、屈服强度和伸长率分别为365 MPa、276 MPa和17.5%。

Microstructures and mechanical properties of extruded Mg-7Gd-5Y-1Nd-xZn-0.5Zr(x=0,1,2)alloys

The microstructure and mechanical properties of extruded Mg-7Gd-5Y-1Nd-xZn-0.5Zr(x=0,1,2,mass fraction,%)alloys were investigated by scanning electron microscope(SEM),transmission electron backscattered diffraction(EBSD)and high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM).The addition of Zn element can form long period stacking ordered(LPSO)structures,promote the precipitation of Mg5(RE,Zn)phases and form Zn-Zr compounds with Zr element.LPSO structures can not only restrict grain growth,refines grain,but also prevent dynamic recrystallization,resulting in dynamic recrystallization grains and deformable grains coexisted,the DRX grains with aá0001?//ED texture,and the deformed grains withá1010?//ED texture.The large size micron-scale Mg5(RE,Zn)particles can reduce the toughness and plasticity of the alloy,the uniformly distributed submicron-scale Mg5(RE,Zn)particles play the role of second phase strengthening and can nail grain boundaries,and hinder grain growth.For three extruded alloys,the Mg-7Gd-5Y-1Nd-2Zn-0.5Zr alloy obtains the optimal mechanical properties,the tensile strength,yield strength and elongation are 365 MPa,276 MPa and 17.5%,respectively.