Microstructure and super high strength of cast Mg-8.5Gd-2.3Y-1.8Ag-0.4Zr alloy

Research highlights: → A super high strength Mg-8.5Gd-2.3Y-1.8Ag-0.4Zr alloy with good ductility is developed using ordinary casting technique and heat treatment. After optimum heat treatment, i.e. solution treatment at 500 deg. C for 10 h and subsequently ageing at 200 deg. C for 32 h, the room temperature TYS, UTS and elongation of the cast-T6 alloy reaches 268 MPa, 403 MPa and 4.9% respectively. → Ag additions produce improved solid solution strengthening and remarkably enhance the age hardening response. The enhanced age hardening response can be attributed to the basal nano-scale plate precipitates, which are not observed in the Ag-free alloy, as well as the refinement of β' phase. The co-precipitation strengthening produced by β' phase and the plate-like precipitate is the largest contributor to the strength of the cast-T6 alloy. → In the paper, we reported a novel super high strength cast magnesium alloy with notable lower rare earth contents and substantially improved ductility. The alloy exhibits a record high ultimate tensile strength of more than 400 MPa with a sufficient elongation of 4.9% at room temperature. Such excellent combination of high strength and ductility is rarely reported in ordinary cast Mg alloys and would be of great significance for the applications of Mg alloys. - Abstract: A super high strength Mg-8.5Gd-2.3Y-1.8Ag-0.4Zr alloy with good ductility was developed using an ordinary casting technique and heat treatment. After the solution treatment at 500 deg. C for 10 h and subsequent ageing at 200 deg. C for 32 h, the room temperature TYS, UTS and elongation of the cast-T6 alloy was 268 MPa, 403 MPa and 4.9% respectively. Ag additions produce improved solid solution strengthening and enhanced the age hardening response. The enhanced age hardening response was attributed to the basal nano-scale plate precipitates, which were not observed in the Ag-free alloy, as well as the refinement of β' phase. The co-precipitation strengthening produced by the β' phase and the plate-like precipitates was deemed to be the largest contributor to the strength of the cast-T6 alloy.