Enhanced strength and ductility of Mg–Gd–Y–Zr alloys by secondary extrusion

The Mg–12Gd–3Y–0.6Zr (GW123, wt.%) alloy was prepared by cast, and thermo-mechanically treated by single and secondary hot extrusion techniques. The microstructure, texture and mechanical properties of the extruded alloy were investigated. The results show that in different treated conditions the microstructure is mainly composed of α-Mg solid solution and second phases of Mg3Y3Gd2 and Mg5(GdY) precipitates. The best mechanical properties are achieved in the secondary extruded alloy after ageing, with the ultimate tensile strength (UTS), tensile yield strength (TYS) and elongation (ɛ) being 446 MPa, 350 MPa and 10.2% at room temperature. A weak texture aligned with 〈101¯0〉||ED (extrusion direction) component and spread from 〈101¯0〉 to 〈112¯0〉 poles was obtained in secondary extrusion, which is caused by the occurrence of dynamic recrystallization (DRX) in shear bands for texture randomization. The fracture modes in extruded GW123 alloy are mixed pattern of transgranular and intergranular fracture, as well as cleavage fracture. The strengthening mechanisms were quantitatively analysed from the different aspects using the measured microstructural parameters. The grain boundaries and solid solution strengthening were the main contributors to the high tensile strength of the GW123 alloy.