Investigation on friction stir processing of gravity die cast AS7U3G aluminum alloy

Abstract

Al Si Mg alloys are widely used to cast high strength components in aerospace and automobile industries However porosity coarse acicular Si particles and coarse aluminum dendrites in the cast structure reduce the mechanical properties of the castings particularly the ductility toughness and fatigue strength Eutectic modifiers and high newlinetemperature heat treatment widely used to modify the cast microstructure cannot eliminate the porosity effectively and redistribute the silicon particles uniformly Friction stir processing a development based on friction stir welding has been proved to be a very effective route to enhance the mechanical properties of cast Al Si alloys Friction stir processing is a solid state process leading to very significant microstructural modifications FSP homogenizes and refines the cast microstructure, completely eliminates porosity and creates a microstructure with fine Si particles distributed in a fine grain aluminum matrix AS7U3G Al alloy used in this investigation is an alloy material of newlineautomotive and energy sectors for engine blocks, steering knuckles etc In this thesis an attempt is made to study the effect of different tool pin profiles tool shoulder profiles multi pass FSP and post FSP heat treatment on microstructure and mechanical properties of AS7U3G Al alloy newline