稀土对过共晶Al-Si合金中共晶Si变质效果的热分析

Thermal Analysis on Modification Effects of RE on Eutectic Si Phase in Hypereutectic Al-Si Alloy

利用热分析系统研究了稀土对Al-20Si-1.5Cu-1Ni-0.4Mg合金中的共晶Si变质效果。在保持初晶Si变质剂P的加入量为0.08%时,对共晶Si变质剂RE的不同加入量下的热分析曲线和金相组织进行了研究。结果表明,随着RE加入量的增加(≤0.6%),共晶Si逐渐从长针状转变为弥散的短杆状,晶粒尺寸减小,共晶生长温度tEG不断降低,共晶生长温度差值ΔtEG不断增大,变质效果越来越好。当RE加入量超过0.6%时,tEG开始上升,ΔtEG开始减小,变质效果变差。共晶生长温度差值ΔtEG与共晶Si的稀土变质效果之间有良好的对应关系。

With the help of thermal analysis system,the modification effects of RE on eutectic Si in Al-20Si-1.5Cu-0.4Mg alloy were investigated. Thermal analysis curves and microstructure of the eutectic Si with various RE additions were observed at a given P content of 0.08%. The results reveal that when RE addition is lower than 0.6%,with its increase,eutectic Si phase in the alloy is gradually converted from acicular structure into dispersedly short rod with decreasing in grain size,where eutectic growth temperature is decreased and difference of eutectic growth temperature is increased,showing better and better modification effects. However,with RE addition more than 0.6%,modification effects become worse,and eutectic growth temperature is increased with decreasing in difference of eutectic growth temperature. Difference of eutectic growth temperature exhibits desirable corresponding relationship with the modification effect of RE on eutectic Si.