Abstract:Ageing hardening, microstructure and mechanical properties of Mg-xY-1.5LPC-0.4Zr (x=0, 2, 4, 6) alloys (LPC represents La-based rare earth metal) were investigated. It was found that the age hardening was enhanced, the grains became finer and the tensile strength was improved with the increase of Y content in Mg-Y-1.5LPC-0.4Zr alloy. The results show that the formed precipitates responsible for age hardening change from fine hexagonal-shaped equilibrium Mg₁₂RE phase to metastable β′ phase with orthorhombic-bc crystal structure when Y is added into Mg-1.5LPC-0.4Zr alloy, and the volume fraction of precipitate phases also increases. The cubic-shaped β-Mg₂₄Y₅ precipitate phases were also observed at grain boundaries in Mg-6Y-1.5LPC-0.4Zr alloy. The distribution of prismatic shaped β′ phases and cubic shaped β-Mg₂₄Y₅ precipitate phases in Mg matrix may account for the remarkable enhancement of tensile strength of Mg-Y-LPC-Zr alloy. The Mg-6Y-1.5LPC-0.4Zr alloy exhibits maximum tensile strength at peak-aged hardness, and the values are 250 MPa at room temperature and 210 MPa at 250 °C.

Key words: magnesium alloy; rare earth; yttrium; age hardening; precipitate phases