Abstract
Effect of porosities on the fatigue properties of high-pressure die cast aluminium alloy is addressed. Three-dimensional shape and location of porosities in the specimen were inspected by the X-ray CT to determine which pore affects the fatigue crack. The tension-compression fatigue test was carried out and the CT inspection was also conducted for all the specimens before and after the fatigue test. By comparing the CT inspection with the SEM observation of the fracture surface, we confirmed that the crack initiation was restricted to shrinkage pores near the specimen surface, and the inner large pores were not the source of fatigue crack. But we found that a cluster of shrinkage cavities can initiate a crack and affect the fatigue fracture although it exists far inside. Multiple cracks were also found on the bumpy fracture surface, and they seemed to reduce the fatigue life by coalescing into a single large crack. Moreover, we demonstrated the successive CT inspection during the fatigue test, and showed its availability to detect the fatigue crack propagation behavior.
