Intermetallic phases observed in non-modified and Sr modified Al–Si cast alloys containing mischmetal

Abstract

An extensive study was carried out to investigate the types of intermetallic phases observed in non-modified and Sr modified A319·1, A356·2 and A413·1 alloys with 0, 2, 4 and 6 wt-% mischmetal (MM) additions and solidified under high and low cooling rate conditions. Quantification of the intermetallics was carried out using electron probe microanalysis and revealed that the total surface fraction of intermetallic phases increased with the addition of MM to the alloys. Wavelength dispersion spectroscopic analysis was employed to identify these phases. In addition to the Al2Cu phase in A319·1 alloy, the Mg2Si phase in A356·2 alloy and the platelet-like β-Al5FeSi and α-Al15(MnFe)3Si2 and α-Al15(MnFeNiCu)3Si2 Chinese script-like iron intermetallic phases in the A413·1 alloy, various MM containing intermetallic phases were observed at high and low cooling rates, each exhibiting a specific Ce/La ratio and morphology. Many of these MM containing intermetallic phases were found to contain Sr, which confirmed the interaction of MM with Sr. Thus, the effectiveness of Sr as a modifier of the eutectic Si phase in these alloys would be reduced.