Parameters controlling the microstructure of Al-11Si-2.5Cu-Mg alloys

摘要

This study investigated the effects of cooling rate during solidification, heat treatment, and the addition of Mn and Sr on the formation of intermetallic phases in Al-11Si-2.5Cu-Mg alloys. Microstructures were monitored using optical microscopy and EPMA techniques. The results reveal that the volume fractions of intermetallic phases are generally much lower in the furnace-cooled samples than in the air-cooled ones due to the dissolution of the p-AlFeSi and Al_2Cu phases during slow cooling at critical dissolution temperatures. Strontium additions increased the volume fraction of the Al_2Cu phase in the as-cast conditions at low and high cooling rates, as well as at varying ranges of Mn levels. Platelets of the p-AlFeSi phase were to be observed in the microstructure of the as-cast air-cooled samples with a DAS of 40 urn at both Mn levels, while none of these particles were to be found in the furnace-cooled samples with a DAS of 120 urn. Sludge particles were observed in almost all of the air-cooled alloys with sludge factors of between 1.4 and 1.9. These particles, however, were not observed in the furnace-cooled alloys with similar sludge factors. Solution heat treatment coarsens the Si particles in the non-modified alloys under both sets of cooling conditions studied, in the Sr-modified alloys, solution treatment has varied effects depending on the cooling rate and the level of Mn present.