Effect of Zr addition on the recrystallization of P/M Al–Cu–Mg alloys

Effects of zirconium and manganese additions on microstructure and tensile property of cold worked and T6 heat-treated Al–4.5 mass%Cu–1.5 mass%Mg–0.6 mass%Mn rapidly solidified powder metallurgy (RSP) alloys were examined. The tensile strength of the Al–4.5 mass%Cu–1.5 mass%Mg–0.6 mass%Mn alloy was somewhat reduced by cold working followed by heat treatment. After the treatments, grains of the alloy were fairly coarse depending on the reduction-ratio in the cold working. TEM observations clarified that the Hall-Petch relation was maintained between 0.2% proof stress and the sub-grain diameter. The tensile strength after the treatments was hardly affected by increasing the manganese content from 0.6% to 1.2%, whereas the strength reduction after the recrystallization was effectively suppressed by adding more than 0.5% zirconium. Zirconium has a significant effect on retarding the growth rate of recrystallized grains, which is caused by homogeneous precipitation of meta-stable Al3Zr (L12) fine particles which are coherent with the matrix.