Enhanced tensile properties of as-cast Mg-10Al magnesium alloy via strontium addition and hot working

Abstract

The lightweight magnesium–aluminum alloys are extensively used in automotive and aerospace industries due to their high-specific strength and low alloying cost, Grain refining via alloying and hot deformation is known as a viable technique for the enhancement of mechanical properties of these alloys. Accordingly, in the present work, grain size refinement and improvement of tensile properties of Mg-10Al magnesium alloy ingot via strontium addition (up to 1 wt%) and hot working (extrusion process) were studied. It was revealed that the addition of Sr up to 0.05 wt% leads to grain refinement of Mg-Al-Sr alloys with the resulting best strength-ductility combination. The as-cast alloys were quite brittle with total elongations well below 5% and their ultimate tensile strength (UTS) values were below 200 MPa, which was attributed to the coarse as-cast structure with a high content of brittle intergranular β-Mg17Al12 phase. It was also found that the aspect ratio of the Al4Sr particles increases by increasing strontium content, which contributes to the deterioration of tensile properties at high strontium contents. Homogenization treatment at elevated temperatures led to the dissolution of the β phase, while the thermally stable Al4Sr particles remained undissolved. The extruded alloys showed remarkably higher strength and ductility compared to the as-cast ingots, which were related to the remarkable grain refinement induced by the recrystallization processes during the hot extrusion process, the disappearance of the deleterious network of the intergranular eutectic constituent, and providing high solute Al content. As a result, UTS of ~ 406 MPa and total elongation of ~ 24% were obtained for the extruded alloy with 0.05 wt% Sr.