Comparative study of extrudability, microstructure, and mechanical properties of AZ80 and BA53 alloys

The extrudability, microstructural characteristics, and tensile properties of the Mg–5Bi–3Al (BA53) alloy are investigated herein by comparing them with those of a commercial Mg–8Al–0.5 Zn (AZ80) alloy. When AZ80 is extruded at 400 °C, severe hot cracking occurs at exit speeds of 4.5 m/min or more. In contrast, BA53 is successfully extruded without any surface cracking at 400 °C and at high exit speeds of 21–40 m/min. When extruded at 3 m/min (AZ80–3) and 40 m/min (BA53–40), both AZ80 and BA53 exhibited completely recrystallized microstructures with a 〈10–10〉 basal texture. However, BA53–40 has a coarser grain structure owing to grain growth promoted by the high temperature in the deformation zone. AZ80–3 contains a continuous network of Mg₁₇Al₁₂ particles along the grain boundaries, which form via static precipitation during natural air-cooling after the material exits the extrusion die. BA53–40 contains coarse Mg₃Bi₂ particles aligned parallel to the extrusion direction along with numerous uniformly distributed fine Mg₃Bi₂ particles. AZ80–3 has higher tensile strength than BA53–40 because the relatively finer grains and larger number of solute atoms in AZ80–3 result in stronger grain-boundary and solid-solution hardening effects, respectively. Although BA53 is extruded at a high temperature and extrusion speed of 400 °C and 40 m/min, respectively, the extruded material has a high tensile yield strength of 188 MPa. This can be primarily attributed to the large particle hardening effect resulting from the numerous fine Mg₃Bi₂ particles.