Effect of erbium on microstructure and mechanical properties of Al‐Si‐Mg‐Cu alloy

Abstract The effect of erbium addition at different ratios (0.2 wt.%, 0.4 wt.%, 0.6 wt.%) on microstructure evolution and mechanical properties of the Al−Si‐Mg−Cu alloy have been investigated. The results show that adding erbium can refine the primary α‐aluminum grains in the as‐cast alloys to a diverse extent. In addition, the coarse and long plate‐like eutectic silicon can be modified into a fine short rod‐like structure, and the distribution of eutectic silicon can be optimized. During the solidification of the alloy, erbium and other elements will form primary erbium‐rich precipitates of different sizes and shapes, including primary erbium‐silicon‐rich and erbium‐copper‐silicon‐rich precipitates, which can change the distribution of solute atoms and promote the evolution of microstructure. But the coarse primary precipitates will embrittle the alloys and consume more solute atoms (erbium, copper, magnesium), having a certain inhibitory effect. After heat treatment, the solid solution decomposes to form secondary Al 3 Er precipitates, which further strengthens the alloy. In particular, the alloy with the highest erbium content shows the best comprehensive tensile properties at as‐cast and heat‐treatment conditions.