Effect of Al addition on microstructure and mechanical properties of Mg-Gd-Zn alloys

The microstructure evolution and mechanical properties of Mg-15.3Gd-1Zn alloys with different Al contents (0, 0.4, 0.7 and 1.0 wt.%) were investigated. Microstructural analysis indicates that the addition of 0.4 wt.% Al facilitates the formation of 18R-LPSO phase (Mg12Gd(Al,Zn)) in the Mg-Gd-Zn alloy. The contents of Al11Gd3 and Al2Gd increase with the increase of Al content, while the content of (Mg,Zn)(3)Gd decreases. After homogenization treatment, (Mg,Zn)(3)Gd, 18R-LPSO and some Al11Gd3 phases are transformed into the high-temperature stable 14H-LPSO phases. The particulate Al-Gd phases can stimulate the nucleation of dynamic recrystallization by the particle simulated nucleation (PSN) mechanism. The tensile strength of the as-rolled alloys is improved remarkably due to the grain refinement and the fiber-like reinforcement of LPSO phase. The precipitation of the beta'phase in the peak-aged alloys can significantly improve the strength. The peak-aged alloy containing 0.4 wt.% Al achieves excellent mechanical properties and the UTS, YS and elongation are 458 MPa, 375 MPa and 6.2%, respectively.