Effect of casting and homogenizing treatment conditions on the formation of Al-Fe-Si intermetallic compounds in 6063 Al-Mg-Si alloys

The effect of casting and homogenizing treatment conditions on the formation of several Al-Fe-Si intermetallic compounds in 6063 aluminum alloy 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 different cooling rates ranging from 0.06 to 50 K/s, following the homogenization at 858 K for 54 ks and 2400 ks. The Al-Fe-Si compound particles were extracted from the alloy ingots using the thermal phenol method. The as-cast 0.1 mass% Fe ingot obtained at the casting cooling rate of 0.06 K/s had a largest amount of the β phase among the ingots investigated. When this ingot was homogenized at 858 K for 54 ks and 2400 ks, the amount of the β phase decreased, while that of the α′ phase increased. On the other hand, the as-cast 0.5 mass% Fe ingot obtained at the casting cooling rate of 50 K/s had the largest amount of the α phase among the ingots investigated. When this ingot was homogenized at 858 K for 54 ks, a large amount of the α phase remained. However, the homogenization at 858 K for 2400 ks resulted in the transformation of the α phase to the α′ phase. The main phase in the as-cast 0.2 mass% Fe ingot obtained at the casting cooling rate of 5 K/s, close to the industrial cooling rates, was the β phase. The β phase gradually decreased, and the relative amounts of the α and α′ phases increased during homogenization at 858 K for 54 ks. Furthermore, almost all of the Al-Fe-Si intermetallic compounds were transformed into the α′ phase in the ingots homogenized at 858 K for 2400 ks.