稀土元素Gd、Nd对AZ80镁合金组织和力学性能的影响

Effects of Rare-Earth Elements Gd and Nd on Microstructure and Mechanical Properties of AZ80 Magnesium Alloy

通过金相、扫描电镜、电子探针和力学性能测试等方法研究了稀土元素Gd和Nd对AZ80镁合金铸态和挤压态组织和力学性能的影响。结果表明,适当添加稀土元素可以使AZ80镁合金的铸态树枝晶基本消失,晶界处层片状Mg17Al12相增多。均匀化后晶粒尺寸明显减小。合金经挤压后均发生了动态再结晶,动态析出的β相沿着再结晶晶粒的晶界分布。加入2%RE(Gd,Nd)后,析出相阻碍再结晶晶粒长大和粒子激发形核再结晶共同作用起到了细晶强化的效果,且高硬质Al2Gd和Al2Nd相能有效阻碍位错运动从而大幅度提高了合金的屈服强度。随着RE(Gd,Nd)含量的增多,β相析出减少,稀土相颗粒变大,弱化了动态再结晶效果,导致应力集中,强度下降。当加入2%RE(Gd,Nd)时其抗拉强度最大,综合性能较好。

The effects of Gd and Nd addition on microstructures and tensile properties of as-cast and extruded AZ80 magnesium alloy was investigated using OM, SEM, EPMA and mechanical property tests. The results show that the appropriate rare earth elements can improve the microstructures of as-cast AZ80 magnesium alloy with dendrite disappearing and more Mg17Al12 lamellar phase appearing along the grain boundaries. Grain size is reduced after homogenization. Dynamic recrystallization （DRX） occurs after extrusion and dynamically precipitated β phase distributes along the recrystallized grain boundaries in all the alloys. When adding 2% RE （Gd, Nd）, the precipitated β phase hinders the grain growth and particle stimulated nucleation plays a common role in fine-grain strengthening. The highly rigid Al2Gd and Al2Nd phase can effectively impede dislocation movement and thus improve the yield strength. With the increase of RE （Gd, Nd） content, β phase precipitation decreases, RE phase particles become larger which weakens the effect of dynamic recrystallization and leads to stress concentration and strength decrease. The maximum tensile strength and best comprehensive performance can be achieved by adding 2% RE（Gd, Nd）.