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Fatigue behaviour of hot worked cast aluminium alloys with different Si contents

Abstract Cast aluminium alloy has sometimes been utilised for various products after applying plastic working combining with heat treatment. The thermomechanical treatment will bring not only positive effects (workhardening and grain refinement) but also negative effects (damage on particles and increase of porosity) on the mechanical properties in the cast aluminium alloy. In this study, the relation between microstructures and fatigue properties has been investigated in hot forged and heat treated Al–Si–Mg casting alloys with different Si contents. An ex situ observation of fatigue crack propagation showed different crack behaviours depending on the microstructures arising from the different Si contents. The crack in the α phase propagated quickly in comparison with the crack located in the eutectic and grain boundaries in the Al–3·1Si–0·4Mg alloy. The crack propagation rate was not constant in the Al–7·7Si–0·4Mg alloy due to the agglomerated Si particles in the eutectic region.