Fracture Behavior of Low-Pressure Sand-Cast Mg–Gd–Y Magnesium Alloy Under Different Types of Loads

The large-scale and complex-shaped sand castings of magnesium-rare earth (Mg-RE) alloys have broad application prospects in the aerospace field. Therefore, it is necessary to study the mechanical properties, especially the fracture behavior of the Mg-RE sand castings based on the reliability and safety requirements of the structural design. In this study, the mechanical behavior of Mg-10Gd-3Y-0.5Zr alloy in the as-cast and the peak-aged states are systematically studied under the quasi-static, impact, and cyclic loads. The initiation and propagation of the cracks under different load conditions are also emphatically discussed. The research results show that the micro-cracks in the sand-cast alloy are easy to initiate in the eutectics under quasi-static and impact loads and then propagate into the grain along the twin interface. The β' precipitates uniformly distributed in the matrix after the T6 treatment can improve the strength and deformation resistance of the matrix, thus leading to higher mechanical properties under the quasi-static and impact loads. In addition, the β' phases in the T6-treated alloy can inhibit the formation of twins, and the dislocation slip is the only deformation mechanism. The micro-cracks are mainly formed at the slip bands and cause failure under the high cycle fatigue load.