Microstructure and mechanical properties of a newly developed high strength Mg54.7Cu11.5Ag3.3Gd5.5Sc25 alloy

Starting from the bulk glass-forming composition Mg59.5Cu22.9Ag6.6Gd11, the development of a bulk glassy matrix composite alloy with high strength and ductility was attempted by adding a large amount of Sc to induce the formation of the MgSc intermetallic compound. However, copper-mould casting of the modified composition, Mg54.7Cu11.5Ag3.3Gd5.5Sc25, as rods with 3 and 5 mm diameter, yields besides the expected MgSc, a second (CuSc) and a third (Mg3Gd-type) intermetallic. These compounds are surrounded by a Mg-rich matrix, possibly composed of glassy regions and a Mg-based terminal solid solution. Although the obtained microstructure deviates largely from the expected one, the new alloy exhibits very high strength, i.e. 790 MPa, and visible plastic deformation, i.e. 0.9%. Shear dimples were found in MgSc.