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 Kls had a largest amount of the beta phase among the ingots investigated. When this ingot was homogenized at 858 K for 54 ks and 2400 ks, the amount of the beta phase decreased, while that of the alpha' 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 alpha phase among the ingots investigated. When this ingot was homogenized at 858 K for 54 ks, a large amount of the alpha phase remained. However, the homogenization at 858 K for 2400 ks resulted in the transformation of the alpha phase to the alpha' 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 beta phase. The beta phase gradually decreased, and the relative amounts of the alpha and alpha a' phases increased during homogenization at 858 K for 54 ks. Furthermore, almost all of the Al-Fe-Si intermetallic compounds were transformed into the alpha' phase in the ingots homogenized at 858 K for 2400 ks. (C) 1999 Kulwer Academic Publishers.