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 Al 2 Cu phase in A319?1 alloy, the Mg 2 Si phase in A356?2 alloy and the plateletlike b-Al 5 FeSi and a-Al 15 (MnFe) 3 Si 2 and a-Al 15 (MnFeNiCu) 3 Si 2 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.

Effect of Solidification Rate and Rare Earth Metal Addition on the Microstructural Characteristics and Porosity Formation in A356 Alloy

“…It is evident from Figure 6(b) that addition of 3% RE to the base alloy has no significant modification effect in spite of the observed decrease in the eutectic temperature. Thus, in this case, the observed depression in the eutectic temperature should not be used as an indicator of modification [11]. When the base alloy is treated with 100 ppm Sr (Figure 6(c)), the microstructure is fully modified.…”

“…Although all rare earth elements have some effect on the eutectic silicon as they are within the atomic radii range predicted by models to be effective in producing growth twins in an Al-Si alloy ( / Si = 1 : 65), however, they only result in a minor refinement of the plate-like silicon morphology. El Sebaie et al [10,11] studied the effects of mischmetal (MM), cooling rate, and heat treatment on the eutectic Si particle characteristics of A319.1, A356.2, and A413.1 Al-Si casting alloys. Measurements of the eutectic Si particles revealed that addition of mischmetal led to partial modification, while full modification was achieved with the addition of Sr in the as-cast condition, at both high and low cooling rates.…”

Effects of La and Ce Addition on the Modification of Al-Si Based Alloys

“…The reason for such unexpected behavior is not well established. Elsebaie et al [21][22][23][24] studied the effects of mischmetal, cooling rate, and heat treatment on the eutectic Si particle characteristics of Al-Si casting alloys. Eutectic Si particle measurements revealed that partial modification was obtained in the as-cast condition with the addition of mischmetal, while full modification was achieved with the addition of Sr, at both high and low cooling rates.…”

Rare Earth Metal‐Based Intermetallics Formation in Al–Cu–Mg and Al–Si–Cu–Mg Alloys: A Metallographic Study

“…Intermetallic phases in nonmodified and Sr-modified Al-Si cast alloys containing mischmetal (MM) were investigated by Elsebaie et al [5] who reported the formation of two distinct intermetallic phases at high solidification rate with the addition of 6 wt.% MM to A356.2 alloy: (i) a grey sludge phase containing Ti with a high Ce/La ratio (3 : 4 : 1) and low Mg content (0.26 wt.%), and (ii) a white spherical phase with a low Ce/La ratio (1 : 32 : 1) with Sr content of 1.5 wt.% and 0.4 wt.%Mg. is white spherical phase was also observed at low solidification rate, having the same chemical composition but exhibiting larger sized particles.…”