Three-dimensional crack initiation behavior of cast aluminum alloy under low-cycle fatigue

The crack initiation mechanism of cast aluminum alloy was addressed to quantitatively evaluate the fatigue strength. We employed the synchrotron radiation microtomography to visualize the three-dimensional damages around pores and silicon particles. Two types of specimens underwent a low-cycle fatigue test. The temperature of solution treatment was different, and it yielded a difference in the shape, size and distribution of silicon particles. After a certain cycles of fatigue, a catastrophic damage around many silicon particles occurred, and they connected to each other so as to form a crack especially within the high stressed region around a relatively large pore. The scanning electron microscopy after the test showed that the type of damage was the breakage of long-shaped silicon particles or the aluminum-silicon interface debonding of round silicon particles. The high temperature solution treatment facilitated the interface debonding by the enlargement of silicon particles.