Effect of homogenizing treatment on type of Al-Fe-Si phases in 6063 aluminum alloy ingots

The effecf of homogenizing treatment on the type of Al-Fe-Si intermetallik compound phases in 6063 aluminum alloys was investigated using X-ray diffraction and transmission electron microscopy (TEM). The four kinds of alloys containing 0.1 to 0.5 mass%Fe were melted and then cooled at three cooling rates ranging from 0.06 to 50 K/ s, followed by the homogenization at 858 K for 54 ks and 2.4 Ms. The Al-Fe-Si compound particles were extracted from the alloy ingots using the thermal phenol method. A large amount of the β phases (monoclinic: a=b=0.612 nm, c=4.15 nm, β=91°) were found in the ingot containing 0.1 mass%Fe obtained by casting cooling rate of 0.06 K/s. When that ingot was homogenized at 858 K far 54 ks and 2.4 Ms, the amount of the β phases had a tendency to decrease, and that of the α′ phases (hexagonal: a=1.23 nm, c=2.62 nm) had a tendency to increase. Moreover, a large amount of the α phases (cubic: a=1.252 nm or 1.256 nm) were found in the ingot containing 0.3 mass%Fe obtained by casting cooling rate of 50 K/s. When that ingot was homogenized at 858 K for 54 ks, a large amount of the α phases remained like the as-cast ingot. However, in that ingot homogenized at 858 K for 2.4 Ms, the main Al-Fe-Si compound particles changed from the α phase to the α′ phase. In the 0.2 mass%Fe ingot at the casting cooling rate of 5 K/s, as solidified condition of commercial alloys, the β phase gradually decreased and the relative frequency of the α phase increased from 10% to 40% in homogenizing at 858 K for 54 ks. However, that of the α′ phase also increased to 50% in homogenized ingot. Furthermore, in that ingot homogenized at 858 K for 2.4 Ms, almost all the Al-Fe-Si compound particles were the α′ phase.