Hall–Petch relationship in friction stir welds of equal channel angular-pressed aluminium alloys

The effect of grain size on hardness in the stir zones of friction stir (FS) welds of equal channel angular (ECA)-pressed Al alloys 1050 and 5083 was examined. The hardness was found to be essentially related to grain size through the Hall–Petch relationship in the stir zone of Al alloy 1050. The kH slope of the Hall–Petch equation for the stir zone of Al alloy 1050 was different from the previously reported ones, which was attributed to dynamic recrystallisation during friction stir welding (FSW). On the other hand, the relationship between hardness and grain size in the stir zone of Al alloy 5083 was expressed by the Hall–Petch equation with a change in slope. The change in slope was attributed to the homogeneous distribution of many fine particles.