挤压Mg-Y-Ni-Co合金的显微组织、加工性能及塑性变形行为

Microstructure,Processing Properties and Plastic Deformation Behavior ofan Extruded Mg-Y-Ni-Co Alloy

本工作通过光学显微镜(OM)、X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和万能实验机对挤压Mg-2Y-0.5Ni-0.5Co(%,原子分数)合金的显微组织、加工性能和塑性变形行为进行了研究。挤压合金的显微组织主要由α-Mg、沿挤压方向分布的片层状和细小块状18R-LPSO相、MgY(Co,Ni)_(4)相以及晶粒内细条纹状的14H-LPSO相组成。拉伸测试结果显示,挤压合金具有良好的室温塑性,断裂延伸率均高于15%。随着温度的升高和应变速率的降低,合金的拉伸强度降低,而塑性增强。合金在300℃、1×10^(-3)s^(-1)和1×10^(-4)s^(-1)应变速率下断裂延伸率分别为117.87%和143.9%,具有准超塑性。通过构建的热加工图谱,优化出合金的稳定加工区间为温度275~300℃、应变速率10^(-4)~10^(-3)s^(-1)。挤压合金的变形行为随温度和应变速率的变化而改变,在低温(室温(RT)到200℃)和不同应变速率下,合金的变形机制以位错滑移为主;在高温(300℃)和低应变速率(1×10^(-4)s^(-1)和1×10^(-3)s^(-1))下,合金的变形机制为晶界滑移协调的位错滑移。

The microstructure,processing properties and plastic deformation behavior of an extruded Mg-2Y-0.5Ni-0.5Co(at%)alloy were investigated by optical microscopy(OM),X-ray diffractometer(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),and universal experiment machine.The microstructure of the extruded alloy mainly consisted ofα-Mg,lamellar and blocky 18R-LPSO phase distributed along the extrusion direction,MgY(Co,Ni)_(4)phase,and fine strip-like 14H-LPSO phase in the grain interior.Tensile test results showed that the extruded alloy had good room temperature plasticity and its elongation to failure was higher than 15%.With increasing temperature and decreasing strain rate,the tensile strengths of the alloy decreased,while the plasticity increased.The alloy exhibited quasi-super plasticity with elongation to failure of 117.87%and 143.9%at 300℃under the strain rates of 1×10^(-4)s^(-3)and 1×10^(-4)s^(-1),respectively.The constructed thermal processing profile was optimized for the stable processing interval of the extruded alloy:275—300℃with strain rates from 1×10^(-4)s^(-1)to 1×10^(-3)s^(-1).The deformation behavior of the extruded alloy varied with temperature and strain rate.At low temperatures(RT—200℃)and different strain rates,the deformation mechanism of the alloy was dominated by dislocation slip.At high temperature(300℃)and low strain rates(1×10^(-4)s^(-1)and 1×10^(-3)s^(-1)),the deformation mechanism of the alloy was dislocation slip coordinated by grain boundary slip.