Microstructure and strengthening mechanism of a thermomechanically treated Mg–10Gd–3Y–1Sn–0.5Zr alloy

The microstructural evolution of a thermomechanically treated Mg–10Gd–3Y–1Sn–0.5Zr (wt%) alloy and its effect on mechanical properties were investigated; a cuboid-shaped Mg2(Sn,Y)3Gd2 was observed in a homogenized/hot-extruded condition. Precipitations involving Mg5(Gd,Y)-particles, Mg3(Gd,Y)-β″(D019), Mg5(Gd,Y)-β′(bco) and β1(fcc) were identified during isothermal ageing; the metastable β′ phase is the key factor for the enhancement in both the Vickers hardness and the tensile strength. The highest ultimate tensile strength (UTS) up to 352 MPa was achieved when aged at 200 °C for 100 h post extrusion. Existing traditional strengthening models were employed to account for the strength improvement of thermomechanically treated alloys and their individual contribution was estimated. The results showed that precipitation strengthening played a much more prominent role.