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

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 Alm(Fe,Mn) and Al3(Fe,Mn) instead of Al6(Fe,Mn) and Al3(Fe,Mn). The evolution of the relative fraction of the Alm(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