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

Cast aluminium alloy has sometimes been utilised for various products after applying plasticworking combining with heat treatment. The thermomechanical treatment will bring not onlypositive effects (workhardening and grain refinement) but also negative effects (damage onparticles and increase of porosity) on the mechanical properties in the cast aluminium alloy. In thisstudy, the relation between microstructures and fatigue properties has been investigated in hotforged and heat treated Al-Si-Mg casting alloys with different Si contents. An ex situ observationof fatigue crack propagation showed different crack behaviours depending on the microstructuresarising from the different Si contents. The crack in the α phase propagated quickly incomparison with the crack located in the eutectic and grain boundaries in the Al-3·1Si-0·4Mgalloy. The crack propagation rate was not constant in the Al-7·7Si-0·4Mg alloy due to theagglomerated Si particles in the eutectic region.