Solidification structures and phase selection of iron-bearing eutectic particles in a DC-cast AA5182 alloy

Abstract

The solidification structures of a commercial DC-cast AA5182 alloy have been studied through the thickness of a rolling ingot. The dendrite arm spacing, grain size, size of primary eutectic particles and macro segregation in the ingot have been measured. The types of the iron-bearing primary particles in the as-cast alloy have been identified by using electron microprobe and selected area electron diffraction pattern in TEM. It has been found, for the first time, that the dominant iron-bearing primary particles are Al m (Fe,Mn) and Al 3(Fe,Mn) instead of Al 6(Fe,Mn) and Al 3(Fe,Mn). The evolution of the relative fraction of the Al m (Fe,Mn) particles in the alloy through the thickness of the ingot has been measured. The phase selection principle for the iron-bearing primary particles in the alloy is discussed with reference to the phase diagram and growth kinetics of the different intermetallic phases.