Effects of Sr, Ti-B and cooling rate on solidification structures of Al-Si-Cu cast alloy

摘要

The effects of cooling rate and addition of Sr and Ti-B on microstructural features such as grain size, dendrite arm spacing, morphologies of eutectic silicon and iron rich compound were investigated for the Al-6.55 % Si-2.78 % Cu-0.59 % Fe-0.38 % Mg-0.34 % Mn alloy (JIS AC4B) . This alloy solidifies in the order of primaryα (Al) , α+α-AlFeMnSi eutectic, α+ Si eutectic, α+β-AlFeMnSi eutectic, α+ Si + Mg{sub}2Si eutectic andα+ Si + Al{sub}2Cu eutectic. The grain size, dendrite arm spacing,size of eutectic silicon particles and length of needle-like iron rich compound decrease as the cooling rate increases, and they are in linear relation on the logarithmic scale. The addition of a small amount of Ti-B markedly refines the grain size whilepractically unaffects the other solidification structures. At the cooling rates of 2.7 K/s, 14.4 K/s and 108.1 K/s, the eutectic silicon crystals fully modify with the addition of Sr more than 60 ppm, 13 ppm and 5 ppm respectively. The addition of Sr anda higher cooling rate tends to increase the formation of Chinese script type iron rich compound.