Effect of Heat Treatment on Microstructure and Mechanical Properties of Mg-Gd-Zn-Ti-xAl Alloys

The microstructure evolution and mechanical properties of Mg-12Gd-1Zn-0.6Ti-xAl alloys under different heat treatment conditions were studied. The results show that the as-cast Mg-12Gd-1Zn-0.6Ti alloy is composed of the α-Mg matrix and (Mg,Zn)3Gd phase. With the increase of Al element, Mg12Gd(Al,Zn) (18R-LPSO), Al2Gd and Al11Gd3 phases are formed in the microstructure. Following the homogenization process, the phases of (Mg,Zn)3Gd, 18R-LPSO, and a portion of Al11Gd3 undergo a transformation into the more stable Mg12Gd(Al,Zn) (14H-LPSO) phases at elevated temperatures. As the Al content increases from 0 to 0.8wt%, the proportion of 14H-LPSO phase significantly increases. The Al2Gd, 14H-LPSO, and Al11Gd3 phases exhibit excellent high-temperature stability. In the peak-aged alloy, the precipitated β′ phases can effectively suppress substrate slip and cause precipitation hardening, thereby improving strength. The Mg-12Gd-1Zn-0.6Ti-0.8Al alloy subjected to peak aging treatment exhibits a good combination of mechanical properties, with a yield strength of 187 MPa, a tensile strength of 290 MPa, and an elongation of 6.8%.