在不同冷却速率下Er对A356合金共晶组织的变质作用

摘要

采用添加稀土元素Er变质处理制备了A356合金,通过控制Er的添加量和不同的冷却速率以改变共晶硅相的形貌.采用金相观察、扫描电镜、透射电镜及能谱分析等测试分析手段研究了铒对A356合金中硅相的变质作用.研究发现:少量的Er添加量(0.3%)就可以明显细化共晶硅相;同时冷却速率对硅相形貌也有显著的影响.在较高的冷却速率250℃/s下,当铒元素的添加量为0.5%时,可以获得细小纤维状的共晶硅相.并对其形貌演变机理做了相应讨论.%The A356 alloy was modified by addition of rare earth erbium.The morphology of the eutectic silicon phase was modified by controlling the erbium addition amount and the cooling rate.The effect of erbium on modification of silicon phase in A356 eutectic alloy was determined by optical microscope, SEM, TEM and EDS.The results reveal that with the addition of 0.3％ erbium, the microstructure of the eutectic silicon phase was refined markedly, and the cooling rate had significant effect on the microstructure of the eutectic silicon phase.At a high cooling rate (250 ℃/s), the addition of erbium (0.5％) was found to promote the formation of fine fibrous silicon phases.The mechanism governing the morphology evolution was also discussed.