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

Abstract

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.