Effects of homogenization temperature on microstructure and mechanical properties of high-speed-extruded Mg–5Bi–3Al alloy

This study investigates the effects of billet homogenization temperature on the dynamic recrystallization behavior during high-speed extrusion and resultant microstructure and tensile properties of the Mg–5Bi–3Al (BA53, wt%) alloy. Two billets homogenized at 350 and 450 °C (350H and 450H billets) are extruded at a high speed of 69 m/min. The 350H billet has a relatively smaller grain size and a higher abundance of fine Mg3Bi2 particles compared to the 450H billet. During extrusion of the 350H billet, enhanced dynamic recrystallization occurs as a result of its finer grains and abundance of particles, while the growth of recrystallized grains is suppressed by the grain-boundary pinning effect of particles. Ultimately, the extruded 350H material is characterized by smaller grains, relatively greater number of Mg3Bi2 particles, and a higher internal strain energy than the extruded 450H material. The tensile strength of the extruded 350H material is higher than that of the extruded 450H material owing to stronger grain-boundary hardening, particle hardening, and strain hardening effects. The extruded 350H material also exhibits a higher tensile elongation as its smaller grains inhibit the formation of crack-inducing undesirable twins during tension. The results from this study demonstrate that a decrease in the homogenization temperature from 450 to 350 °C leads to improved strength and ductility in the high-speed-extruded BA53 material.