挤压比对Mg-1Tm-0.2Ni合金组织及性能的影响

Effect of extrusion ratio on microstructure and mechanical properties of Mg-1Tm-0.2Ni alloy

利用光学显微镜(OM)、扫描电镜(SEM)、电子背散射衍射(EBSD)、透射电镜(TEM)及室温拉伸试验等研究了Mg-1Tm-0.2Ni合金铸态及挤压态的显微组织、织构及力学性能。结果表明,铸态Mg-1Tm-0.2Ni合金的组织主要由α-Mg基体和弥散分布的Mg_(2)(Tm,Ni)第二相组成,晶粒粗大。经430℃挤压后,挤压比为16时,合金呈现出不完全动态再结晶的双峰组织;挤压比为25时,合金呈现出完全动态再结晶的组织,且晶粒细化明显,平均晶粒尺寸为4.76μm;挤压后合金呈现出明显的基面纤维织构(C轴垂直于挤压方向),随着挤压比的增加,织构强度显著下降。由于双峰组织强化和织构强化的共同作用,挤压比为16时合金的力学性能最佳,其屈服强度、抗拉强度和断后伸长率分别为219 MPa、266 MPa和21.5%。

Microstructure,texture and mechanical properties of as-cast and extruded Mg-1Tm-0.2Ni alloy were studied by means of optical microscope(OM),scanning electron microscopy(SEM),electron backscatter diffraction(EBSD)technique,transmission electron microscopy(TEM)and room temperature tensile test.The results show that the microstructure of the as-cast Mg-1Tm-0.2Ni alloy is mainly composed ofα-Mg matrix and dispersed Mg_(2)(Tm,Ni)second phase,and the grain size is coarse.After extrusion at 430℃,when the extrusion ratio is 16,the alloy shows a bimodal structure of incomplete dynamic recrystallization.When the extrusion ratio is 25,the alloy shows a completely dynamic recrystallization microstructure,the grain refinement is obvious,and the average grain size is 4.76μm.After extrusion,the alloy shows obvious basal fiber texture(C-axis is perpendicular to the extrusion direction).With the increase of extrusion ratio,the texture strength decreases significantly.Due to the combined effect of bimodal microstructure strengthening and texture strengthening,the mechanical properties of the alloy are the best when the extrusion ratio is 16,and the yield strength,tensile strength and elongation are 219 MPa,266 MPa and 21.5%,respectively.