Microstructures and mechanical properties of the extruded Mg-4Y-2Gd-xZn-0.4Zr alloys

Microstructures and mechanical properties of the Mg-4Y-2Gd-0.4Zr alloy with Zn additions have been investigated. The investigation suggests that the mechanical properties of the alloys have been greatly improved after hot extrusion due to the refinement of microstructures, especially the elongations. The extruded Mg-4Y-2Gd-1.0Zn-0.4Zr alloy displays excellent tensile properties. The ultimate tensile strength and the yield tensile strength are 291 and 228 MPa, respectively, with an elongation of 28%. The additions of Zn have an obvious effect on refining microstructure of the extruded alloys, and the vicker hardness increases with increasing Zn additions. The age hardening responses of the extruded alloys have been investigated at 220 °C. These alloys display unobvious ageing hardness responses.

Research highlights▶ We found that addition of Zn led to the formation of the LPS structure in the Mg-4Y-2Gd-0.4Zr alloys, and the volume fraction of this structure increased with increasing Zn addition. The LPS structure in both the cast alloys and the extruded alloys has a 14H long periodic ordered structure. This LPS structure has a great effect on improving the mechanical properties. The ageing investigation suggested that these series alloys had no obvious age hardening response. However, the addition of 2% Zn led to a better peak-ageing hardness due to the precipitates of the MgZn2 phase during ageing at 220 °C.