A Formation Map of Iron-Containing Intermetallic Phases in Recycled Cast Aluminum Alloys

The cooling rate-dependent modification effect of Mn on the formation of Fe-containing intermetallic phases during solidification of Al-Si-Mg secondary cast aluminum alloys [containing 0.5 to 1 pct Fe (All compositions are in wt pct unless otherwise stated.)] was investigated by CALculation of PHAse Diagrams (CALPHAD) modeling and solidification experiments. The critical Mn concentration required to prevent the formation of detrimental β-Al₅FeSi was found to be dependent on both the alloy composition (particularly the Fe/Mn ratio) and the cooling rate. A map of Fe/Mn ratio vs cooling rate was created, to summarize the metallurgical conditions of Fe-rich intermetallic phase formation. By understanding such formation conditions, the microstructure of aluminum castings can be controlled to create low-cost secondary alloys with high Fe content.