Effect of plastic deformation and semisolid forming on iron-manganese rich intermetallics in Al-8Si-3Cu-4Fe-2Mn alloy

The effects of plastic deformation and semisolid forming on the iron and manganese-rich intermetallics in Al-8Si-3Cu-4Fe-2Mn alloys were investigated. High volume fraction of alpha-Al-15(Fe,Mn)(3)Si-2 intermetallics were precipitated during melting and solidification of this alloy. The as-cast specimens were deformed plastically in rolling process to achieve 5-15% plastic deformation. Plastic deformation caused fragmentation of brittle intermetallics in Al-Si matrix because of their low formability and also produced alpha-Al spheroids after reheating in semisolid temperature due to recrystallization and partial melting (RAP) process. Microstructural investigations revealed that appropriate semisolid structure with alpha-Al sphericity of 93% and grain size of 64 mu m was obtained after 10-15% plastic deformation of the samples and holding them in 580 degrees C for 15 min. Thixoforming process was performed in 580 degrees C up to 30% deformation on the prepared semisolid feedstocks, which caused re-distribution of the intermetallic particles in the final near net shape part. The mean equivalent diameter of iron-manganese bearing intermetallics decreased from 26-43 mu m in the as-cast condition to 9-11 mu m in the thixoformed samples. The aspect ratio also decreased from 1.7 in the as-cast condition to 1.2 in the thixoformed samples. Reduction of the mean diameter and aspect ratio of intermetallics and their good distribution after thixoforming process will improve tensile strength and formability of the alloy. (c) 2010 Elsevier B.V. All rights reserved.