Abstract:The fracture behavior of a permanent mould casting Mg-8.57Gd-3.72Y-0.54Zr (mass fraction, %) (GW94) alloy was investigated under different thermal conditions, including as-cast, solution-treated, peak-aged, and over-aged states. Scanning electron microscopy (SEM) and optical microscopy (OM) were employed to examine the crack nucleation and fracture model. The results indicate that the GW94 alloy shows different behaviors of crack initiation and fracture under different thermal conditions. During tensile test at room temperature, the fracture model of the as-cast GW94 alloy is quasi-cleavage, while that of the solution-treated alloy is transgranular cleavage. It is a mixed pattern of transgranular and intergranular fracture for both the aged conditions. Large cavities formed at grain boundaries are observed in the peak-aged sample tested at 300 ˚C, corresponding to the intergranular fracture. Localized plastic deformation at grain boundaries is also observed and corresponds to the high elongation at 300 ˚C.

Key words: magnesium alloy; rare earth; Mg-Gd-Y alloys; mechanical properties; fracture behavior; heat treatment