THE EFFECT OF SI CONTENT ON THE SIZE AND MORPHOLOGY OF FE-RICH AND CU-RICHINTERMETALLICS IN AL-SI-CU-MG ALLOYS

摘要

Recent studies have shown that the β-Al_5FeSi and θ-Al_2Cu phase intermetallic particles are refined and dispersed in the presence of high silicon, hence improving the ductility of Al-Si-Cu-Mg alloys. In alloys with low Si content, the Fe- and Cu-rich particles form long and closely intertwined clusters which lead to low ductility. At high Si contents, the intermetallic phases appear more dispersed and the clusters of particles are small and isolated from each other, hence the increased ductility. In this work experiments involving ternary Al-Si-0.8Fe alloys and commercial A319 alloy with different contents of Si are presented. It is shown that, contrary to the conclusions of the earlier work, Si by itself is not responsible for the refining of the Fe-rich intermetallics. This seems to suggest that a synergistic interaction with other elements, possibly Sr and Mn, may be necessary for the refining of the intermetallics to occur. Alternatively, it is speculated that the presence of a low melting point eutectic, in this case the Al-Si-Al_2Cu eutectic, is the reason for the refining and dispersion of intermetallics in the higher Si alloys.