Consideration on stable crack propagation from cast defect in As-cast AZX912 Mg alloy

Mg alloys have the lowest density of metals commonly used as structural materials. A non-combustible Mg alloy with a high ignition point has been developed, and they tend to form cast defects. In order to determine whether a defect in the alloy can be regarded as a crack, tensile tests were conducted on specimens with circumferential notches that simulate a crack by varying the notch root radius. The results of the tensile tests showed that the strengths of the specimens were similar at all radii, and that in one specimen, the crack was initiated and grew stably only from the notch root and did not interfere with the shrinkage porosity. From the observations of longitudinal sections of the specimens subjected to interrupted tensile tests, the path of the stable crack propagation was clarified and the length scale of crack initiation was defined. Based on the comparison between the length scale and the notch depth, and the fact that stable crack propagation occurred from all notch with a 1 mm deep notch, we predict that stable crack propagation always occurs in a fracture process from notches smaller than 1 mm.