Effects of ageing treatment on microstructures and properties of Mg–Gd–Y–Zr alloys with and without Zn additions

Mg–10Gd–3Y–0.5Zr alloys with and without 1% Zn additions have been investigated using optical microscopy, scanning electron microscope and X-ray diffraction. The microstructures, ageing hardening behaviors and mechanical properties of the two alloys are compared. The extruded-T5 specimens exhibit remarkable age hardening responses during ageing from 200 to 250 °C. The highest peak hardness and strength of the two alloys are obtained when they are aged at 200 °C. Addition of 1% Zn to Mg–10Gd–3Y–0.5Zr alloy results in the greater magnitude ageing effect and better mechanical properties as well as better heat resistance. Furthermore, secondary ageing is carried out at 200 °C following preliminary ageing at 250 °C for both Mg–10Gd–3Y–0.5Zr and Mg–10Gd–3Y–1Zn–0.5Zr alloys. The ultimate tensile strength values after secondary ageing are slightly lower compared with the highest strength of the two alloys, but secondary ageing offers a better combination of high strength and ductility.