铸态Mg-2Zn-1.5Cu合金组织及力学性能

利用金相显微镜、扫描电镜、透射电镜、XRD物相分析以及力学性能测试等手段,研究了Mg-2Zn-1.5Cu(at%)合金的显微组织及力学性能。结果表明:铸态合金存在较为明显的元素偏析,主要的第二相为MgCuZn相;合金的力学性能随着温度的提高而不断降低,塑性变化幅度要明显高于强度,合金的断裂方式也由低温时的沿晶断裂转变为高温时的穿晶断裂;在相同温度下,随着应力的提升,合金的稳态蠕变速率提高,蠕变机制由晶界控制转变为晶界及位错共同控制;在相同的应力下,随着温度的提升,合金的稳态蠕变速率存在数量级的提升,蠕变激活能由130kJ/mol降低到36.4 kJ/mol;在200℃,45 MPa时,出现加速蠕变阶段,发生蠕变断裂,断口存在明显的穿晶断裂特征,基体中有大量的沿基面运动的位错,部分位错发生攀移,MgZnCu相具有减缓蠕变变形的作用。

Microstructure and Mechanical Properties of As-cast Mg-2Zn-1.5Cu(at.%) Magnesium Alloy

The microstructure and mechanical properties of Mg-2 Zn-1.5 Cu(at%)alloy were investigated by means of metallographic microscope,scanning electron microscopy,transmission electron microscopy,XRD phase analysis and mechanical properties test.The results show that the as-cast alloy has obvious element segregation,and the main second phase is MgCuZn phase;the mechanical properties of the alloy decrease when the temperature rises,while the plasticity changes are more significant than the strength change,and the fracture mode of the alloy also changes from intergranular fracture at low temperature to transgranular fracture at high temperature;at the same temperature,the steady-state creep rate of the alloy increases and the creep mechanism is transformed from grain boundary control to joint control of grain boundary and dislocation with the increase of the stress;at the same stress,there are orders of magnitude increase in the steady-state creep rate of the alloy with the increase of the temperature,and the creep activation energy decreases from 130 kJ/mol to 36.4 kJ/mol;the alloy reaches an acceleration creep stage at 200°C,45 MPa and creep fracture occurs with obvious transgranular fracture characteristics in the fracture position and a large number of dislocations along the base surface in the matrix.Part of these dislocations climb and the MgZnCu phase has the effect of slowing creep deformation.