The effect of homogenization on microstructures and mechanical properties of Mg-7Gd-3Y-1Nd-xZn-0.5Zr (x = 0.5, 1 and 2 wt.%) alloys

The microstructures evolution and mechanical properties of Mg-7Gd-3Y-1Nd-xZn-0.5Zr (x = 0.5, 1 and 2 wt.%) alloys before and after homogenization have been investigated systemically. Experimental results reveal that the microstructure of the as-cast alloy with 0.5% Zn consists of α-Mg, (Mg, Zn)3RE phase, Mg5 (RE, Zn) phase and stacking fault, the addition of 1% and 2% Zn results in the disappearance of the Mg5 (RE, Zn) phase, but a block-like 14H-LPSO phase is observed in the alloy with 2% Zn. TEM analyses indicate that the (Mg, Zn)3RE and Mg (RE, Zn) phases have a face-centered cubic (fcc) structure with lattice constants of 0.73 nm and 2.23 nm, respectively. After homogenization at 520 °Cfor 32 h, the 14H LPSO phase appear in the alloys with 1% and 2% Zn, but no other phase can be seen in the alloy with 0.5% Zn. The HRTEM results suggest that the stacking sequences of the 14H-LPSO phase are ABABABACBCBCBC. The tensile tests at room temperature (RT) exhibit that as-cast alloy containing 1% Zn shows the optimal mechanical properties and the ultimate tensile strength (UTS), yield strength (YS) and elongation are 187 MPa, 143 MPa and 3.1%, but the mechanical properties of the as-homogenized alloy containing 2% Zn exhibit the highest mechanical properties and the UTS, YS and elongation are 245 MPa, 166 MPa and 12.6%, respectively.