Influence of Sr and Mn additions on intermetallic compound morphologies in Al-Si-Cu-Fe cast alloys

The influence of Sr or Sr and Mn combined additions on the Fe-containing intermetallic compounds in Al-Si-Cu-Fe cast alloys has been investigated using Al-6.5%Si-3.5%Cu-1.0%Fe and Al-6.5%Si-3.5%Cu-1.0%Fe-0.3%Mn alloys (in mass%) with a similar composition to the 319 aluminum alloy. The results show that Sr successfully modifies the large, highly branched beta-needle-like phase (beta: Al5FeSi) into the individual, less-branched and finer one. The combined addition of Mn and Sr results in modification of the needle-like beta-phase as well as promotion of Chinese script and sludge morphology formation. The mechanism of the above morphological changes has been discussed in accordance with the mechanism of nucleation and growth of the beta-needle-like phase during solidification.