微量钒对AZ91D镁合金显微组织的影响

研究了添加微量钒对AZ91D镁合金显微组织的影响。在AZ91D镁合金熔炼过程加入AlV55中间合金引入钒元素,用光学显微镜、扫描电镜、能谱仪和X射线衍射等分析研究了加钒前后合金组织的变化以及钒在合金中的存在形式。结果表明:钒的引入使β-Mg17Al12相由不连续网状逐渐离散化,钒在AZ91D合金中主要以新相Al3V形式溶解或分散于β-Mg17Al12相和α-Mg基体中。高熔点的新相Al3V在AZ91D镁合金凝固过程中先于其他相生成聚集在固液界面前沿,抑制晶粒的长大;同时由于α-Mg相细化而使晶界面积增加,相应的单位面积晶界处发生共晶反应的熔液体积减少,生成的β-Mg17Al12相变得细小。同时由于晶粒尺寸减小以及晶界处Al3V相的强化作用,AZ91D合金的硬度随着添加钒含量的增加呈增大趋势。

Effect of Trace Vanadium on Microstructure of AZ91D Magnesium Alloy

The effect of trace vanadium addition on the microstructure of AZ91D magnesium alloy was investigated.Vanadium was introduced by adding AlV55 master alloy.The microstructure variations before and after vanadium addition and the existence form of vanadium in the alloy were analyzed by OM,SEM,EDS and XRD.The results show that the discontinuously reticulated β-Mg17Al12 phase in magnesium alloy become gradually discrete due to vanadium addition.Vanadium added in AZ91D alloy presents in the form of Al3V phase dissolving or dispersing in the β-Mg17Al12 and α-Mg phase.The mechanism of the microstructure refinement is that Al3V phase,which has a higher melting point,has formed prior to the other phases,gathering on the solid-liquid interface and inhibiting the growth of the grain during the solidification of AZ91D alloy.The increase of the grain boundary area reduces the melt volume of eutectic reaction,resulting in the refinement of β-Mg17Al12 phase.Due to the grain refinement and strengthening of Al3V phase,the brinell hardness of AZ91D alloy increases with the V content increasing.