Heat-treating below recrystallization temperature to enhance compressive failure strain and work of fracture of magnesium

Abstract

New bimetal magnesium/aluminium macrocomposite containing millimeter-scale Al core reinforcement was fabricated using solidification processing followed by hot coextrusion. Microstructural characterisation revealed increased grain size, Mg texture change and unbalanced interfacial interdiffusion of Mg and Al into each other. Stress at the bimetal interface was attributed to solid solution formation, thermal expansion mismatch, unbalanced Kirkendall strain, lattice misfit strain, and strain localization effects, these being interface localized strengthening phenomena. Compressive testing revealed that presence of Al core decreased 0.2% YS (−23%) and ultimate compressive strength (UCS) (−11%), but significantly increased failure strain (+134%) and work of fracture (+60%) of Mg in the as-extruded macrocomposite. Also, interfacial relaxation during heat treating significantly increased failure strain (+17%) and work of fracture (+17%) of Mg/Al macrocomposite without compromising 0.2% YS and UCS. The effects of presence of millimeter-scale Al core as well as interfacial relaxation on the compressive properties of the bimetal macrocomposite are investigated in this paper.