In order to clarify the crack initiation and propagation behaviour of a squeeze cast aluminum-silicon-magnesium alloy, fatigue tests of smooth specimens cut from Al alloy car wheels formed by the squeeze casting were carried out under the constant stress amplitudes. The behaviour of microcracks was monitored successively by the plastic replication method. In addition to the constant stress amplitude tests, fatigue tests under the two-step loading (low-to-high block and high-to-low block loading) were performed. The physical basis of the effect of stress change on fatigue damage was investigated based on the behaviour of small cracks.
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