Improved mechanical properties of high-speed extruded BA53 alloy through long-range water-cooling system

A recently developed Mg–5Bi–3Al (BA53, wt%) alloy exhibited remarkable extrudability despite its high alloying content. However, when subjected to high-speed extrusion with a die exit speed of 67 m/min, grain coarsening of recrystallized grains occurs, increasing their size from 12.1 to 26.4 μm due to excessive heat generation during extrusion. Herein, a long-range water-cooling system is installed immediately after the extrusion die to mitigate grain coarsening and attain finer grains in the high-speed extruded alloy. The results demonstrate that the use of the cooling system leads to a significant reduction in the average grain size (from 26.4 to 15.7 μm) of the BA53 alloy extruded at high speed. Furthermore, grain refinement led to notable increases in the ultimate tensile strength (from 255 to 276 MPa) and elongation (from 7.5% to 8.6%) of the alloy. These enhancements in strength and elongation are primarily attributed to the enhanced grain-boundary hardening effect and suppression of twinning during tension, both of which are consequences of grain refinement. This study underscores the effectiveness of a long-range water-cooling system, comprising water spraying over a length of 2 m, in achieving grain refinement during high-speed extrusion of the BA53 alloy and improving both the strength and ductility of the alloy after high-speed extrusion.