Effect of cooling rate on the occurrence of Al-Fe-Si intermetallic phases in 6063 aluminum alloy ingots

The effect of cooling rate on the occurrence of Al-Fe-Si intermetallic compound phases in 6063 aluminum alloy was investigated in the as-cast state using X-ray diffraction and transmission electron microscopy (TEM). The four alloys containing 0.1 to 0.5 mass%Fe were melted and then cooled at three cooling rates ranging from 0.06 to 5 K/s, and the Al-Fe-Si compound particles were extracted from the alloy ingots using the thermal phenol method. With increasing cooling rate, the amount of a skeleton-shaped α phase increased irrespective of iron content and that of the β phase decreased. When the iron content increased over 0.2%, the amount of the β phase decreased at the intermediate cooling rate (5 K/s). When the iron content decreased from 0.2 to 0.1%, the amount of the β phase also decreased and the α′ phase co-existed. As a result, at a typical Fe content, i.e., 0.2%Fe, in commercial 6063 alloys, the β phase was most frequently formed in comparison with other Fe content, and became the main phase even at the intermediate cooling rate (5 K/s) which was roughly equal to that for the commercial ingots.