Microstructures and mechanical properties of Mg–10Gd–6Y–2Zn–0.6Zr(wt.%) alloy

Microstructures and tensile mechanical properties of Mg–10Gd–6Y–2Zn–0.6Zr alloy were systematically studied. Four phases were found in the as-cast specimen: α-Mg, Mg3(GdYZn), Mg12(GdY)Zn and Mg24(GdYZn)5. The long-period stacking order (LPSO) structure is found, which is the phase of Mg12(GdY)Zn. The LPSO structure has two existing forms: lamellar structure in the inner grains and block-like structure at grain boundaries. 6H-type LPSO structure with a stacking sequence of ABCBCB′ is defined in homogenized specimen, where A and B′ layers are significantly enriched by Gd, Y and Zn. The ageing hardening behavior of as-extruded specimens at 200 °C has been investigated. The ultimate tensile strengths of the as-extruded and peak-aged alloys are 360 MPa and 432 MPa, and the elongations are 18% and 5% respectively. The effective strengthening models have been considered to predict the strength. The results suggested that the sub-micron metastable β′ phase was the main strengthening factor of the peak-aged alloy.

• A high-strength Mg–10Gd–6Y–2Zn–0.6Zr alloy is prepared by conventional casting, extrusion and heat treatment techniques. • 6H-type long-period stacking order structure is identified in homogenized specimen. • The effect of LPSO structure on the mechanical properties of as-extruded Mg–10Gd–6Y–2Zn–0.6Zr alloy is discussed. • Strengthening models are considered to predict the tensile proof strength. • The calculated tensile proof strength partly agrees with the experimental tensile proof strength.