Journal of Magnesium and Alloys (Aug 2024)
Promoting dynamic recrystallization and improving strength and ductility of Mg–7Bi alloy through Al addition
Abstract
This study investigated the influence of the addition of Al to a Mg–7Bi (B7, wt%) alloy, particularly its recrystallization behavior during extrusion and its resulting mechanical properties. The addition of 2 wt% Al to the B7 alloy resulted in a lower grain size, a reduction in the number density of fine Mg3Bi2 particles, and a higher area fraction of relatively coarse Mg3Bi2 particles in the extrusion billet. These microstructural changes increased the nucleation sites for recrystallization, reduced the Zener pinning effect, and enhanced particle-stimulated nucleation, all of which promoted dynamic recrystallization behavior during extrusion. As a result, the area fraction of recrystallized grains in the extruded alloy increased from 77 % to 94 %. The extruded B7 alloy exhibited a strong fiber texture, whereas the extruded Mg–7Bi–2Al (BA72) alloy had a weak – texture, which was attributed to the minimal presence of unrecrystallized grains and the dispersed orientation of the recrystallized grains. The tensile yield strength (TYS) of the extruded BA72 alloy was higher than that of the extruded B7 alloy (170 and 124 MPa, respectively), which resulted from the enhanced grain-boundary and solid-solution strengthening effects. The tensile elongation (EL) of the BA72 alloy also exceeded that of the B7 alloy (20.3 % and 6.1 %, respectively), the result of the uniform formation of fine twins under tension in the former and the formation of a few coarse twins among the unrecrystallized grains in the latter. Consequently, the addition of a small amount of Al to the B7 alloy significantly improved both the strength and ductility of the extruded alloy, resulting in a remarkable increase in the product of the TYS and EL from 756 to 3451 MPa% and expanding its potential range of applications as a lightweight extruded structural component.
