Microstructure refinement and mechanical properties of severely deformed Al–Mg–Li alloys

Abstract

Experiments have been conducted to investigate the possibility of producing aluminium aerospace-alloys, with properties similar to those of the powder metallurgical alloy AA5091, by the potentially cheaper route of spray-casting and severe deformation. Two alloys with compositions based on the commercial alloy AA5091 were spray-cast to obtain a large density of Al 3(Zr,Ti) dispersoids as a substitute for the oxide and carbide particles present in AA5091. The materials were subsequently severely deformed using equal channel angular extrusion (ECAE) to effective strains as high as ten. After deformation the grain sizes in both materials were as fine as 0.3–0.6 μm, while the fraction of high angle grain boundary area was >70%. The severely deformed alloys were stable up to 400 °C, but at higher temperatures abnormal grain growth was observed initiated by the heterogeneous distribution of dispersoid particles inherited from the spray-castings. Encouragingly, for similar heat-treatment conditions, the yield strengths of the experimental materials were found to be comparable to the values specified for the commercial alloy AA5091 while the ductilities were up to three times higher.