Effect of Zn addition on microstructure and mechanical properties of cast Mg-Gd-Y-Zr alloys

The effects of Zn addition on the microstructure and mechanical properties of Mg-10Gd-3Y-0.6Zr (wt.%) alloys in the as-cast, solution-treated, and peak-aged conditions were investigated. Experimental results reveal that the microstructure of the as-cast alloy without Zn consists of alpha-Mg and Mg-24(Gd, Y)(5) phases, and the alloy with 0.5 wt.% Zn consists of alpha-Mg, (Mg, Zn)(3)(Gd, Y) and Mg-24(Gd, Y, Zn)(5) phases. With the addition of Zn increasing to 1 wt.%, the Mg-24(Gd, Y, Zn)(5) phase disappears and some needle-like stacking faults distribute along the grain boundaries. Moreover, the 18R long-period stacking ordered (LPSO) phase is observed in the as-cast alloy with 2 wt.% Zn. After solution treatment, the Mg-24(Gd, Y)(5) and Mg-24(Gd, Y, Zn)(5) eutectic phases are completely dissolved, and the (Mg, Zn)(3)(Gd, Y) phase, needle-like stacking faults and 18R LPSO phase all transform into 14H LPSO phase. Both the suitable volume fraction of 14H LPSO phases and the fine ellipsoidal-shaped beta' phases make the peak-aged alloy with 0.5 wt.% Zn exhibit excellent comprehensive mechanical properties and the UTS, YS and elongation are 338 MPa, 201 MPa and 6.8%, respectively.