Analysis and Discussion on the Room Temperature Microstructure and Properties of High Content Mixed Rare-Earth As-Cast AZ61 Magnesium Alloy

This paper systematically analyzed and discussed the microstructure and mechanical properties of as-cast AZ61 magnesium alloy with rare-earth content of 1.0 similar to 4.0 wt.% by optical microscopy, SEM, EDS, and XRD. The results indicate that in addition to the obvious distribution of skeletal beta-Mg17Al12 phase, a small amount of Mg-32(Al, Zn)(49) quasicrystal phase is distributed in as-cast AZ61 alloy. With the addition of rare-earth content, the skeletal beta-Mg17Al12 phase dendrites in the as-cast AZ61 magnesium alloy matrix are decomposed obviously. The dendrite decomposition is more serious with increased Rare-earth content, and the quasicrystal Mg-32(Al, Zn)(49) disappears. When the rare-earth content is 1%Ce similar to 2%Ce, the alloy mainly consists of needle-like, dot-like, or clustered Al4Ce and Al8Mn4Ce phases with a small amount of Al4La. When 2.8%Ce+1.2%Nd mixed rare-earth was added, the Al8Mn4Ce phase was not found in the alloy but mainly composed of Al3Nd and Al4Ce rare-earth phases. These rare-earth phases were radiative needle-like, willow leaf-like, rod-like, spot-like, layer-like, and a little irregular block. The as-cast AEZ641(2.8 wt.% Ce+1.2 wt.% Nd) magnesium alloy has the best comprehensive performance, and the yield strength is 2% higher than the as-cast AZ61 alloy. Its tensile strength, hardness, and elongation are similar to as-cast AZ61 alloy. The fracture mechanism of as-cast AZ61 + xRE is mainly a cleavage-type brittle fracture.