Development of high mechanical properties and moderate thermal conductivity cast Mg alloy with multiple RE via heat treatment

A new cast Mg–2 Gd–2 Nd–2 Y–1 Ho–1 Er–0.5 Zn–0.4 Zr（wt%） alloy was prepared by direct-chill semicontinuous casting technology. The microstructure, mechanical properties and thermal conductivity of the alloy in as-cast, solid-solution treated and especially peak-aged conditions were investigated. The as-cast alloy mainly consists of β-Mg matrix,（Mg, Zn）;RE phase and basal plane stacking faults. After proper solid-solution treatment, the microstructure becomes almost Mg-based single phase solid solution except just very few RE-riched particles. The as-cast and solid-solution treated alloys exhibit moderate tensile properties and thermal conductivity. It is noteworthy that the Mg alloy with 8 wt% multiple RE exhibits remarkable age-hardening response（ HV = 35.7）, which demonstrates that the multiple RE（RE = Gd, Nd, Y, Ho, Er） alloying instead of single Gd can effectively improve the age-hardening response.The peak-aged alloy has a relatively good combination of high strength/hardness(UTS（ultimate tensile strength） > 300 MPa; TYS（tensile yield strength） > 210 MPa; 115.3 HV), proper ductility（ε≈ 6%） and moderate thermal conductivity(52.5 W/（m K）). The relative mechanisms mainly involving aging precipitation of β￠ and β’’ phases were discussed. The results provide a basis for development of high performance cast Mg alloys.