Effect of Cu on the Precipitation of α-Al(Mn,Cr)Si Dispersoids in an Al-Mg-Si-Mn-Cr Alloy

Nanoscale dispersoids will retard or inhibit recrystallization of aluminum alloys during thermomechanical processes. In the present study, the influence of an addition of 0.6 wt. % Cu on the precipitation behavior of dispersoids in an Al-Mg-Si-Mn-Cr alloy had been investigated. Large amounts of dispersoids with different shapes, e.g. cubic, rod-like and plate-like, were achieved in the experimental alloys after homogenization. Compared with the Cu-free alloy, Cu-added alloy exhibits a higher proportion of cubic shape dispersoid. HRTEM results indicated that the cubic shape dispersoid has an icosahedral quasicrystal structure, while the rod-like or plate-like shape dispersoids show a simple cubic crystal structure. Due to the presence of a high number density of quasicrystalline dispersoids, the Cu-added alloy exhibits a higher recrystallization resistance during hot compression. This study presents a new insight that besides the precipitation strengthening, the Cu alloying in an Al-Mg-Si-Mn-Cr alloy can also contributes to the precipitation of dispersoids.