Novel Mg–Bi–Al alloy with extraordinary extrudability and high strength

A novel high-alloyed Mg–5Bi–3Al (BA53, wt%) alloy with extraordinary extrudability and high strength is developed. It is successfully extruded at a die-exit speed of 67 m/min without any hot cracking, which is over 10 times the maximum extrusion speeds of commercial high-alloyed Mg alloys, e.g., AZ80 and ZK60. The BA53 alloy extruded at 67 m/min shows high tensile yield strengths in the as-extruded and peak-aged states (188 and 214 MPa, respectively). These excellent extrudability and high strength are mainly attributed to the formation of thermally stable Mg₃Bi₂ phase. Undissolved coarse and fine Mg₃Bi₂ particles effectively suppress grain growth during and after extrusion through grain-boundary pinning, leading to the formation of a relatively fine grain structure. Fine rod-type Mg₃Bi₂ precipitates formed on the prismatic plane along the <0001>_Mg direction during air-cooling after existing the die lead to precipitation hardening. The formation of numerous nanosized Mg₃Bi₂ precipitates along the <01¯10>_Mg direction during subsequent aging improves the material strength without ductility loss. The developed BA53 alloy, which comprises inexpensive alloying elements Bi and Al, can be extensively used for manufacturing extruded Mg products because of its high cost-competitiveness, processing efficiency, and mechanical properties.