Influence of Cerium on Texture and Ductility of Magnesium Extrusions

Unalloyed Mg and Mg-0.2%Ce alloy were extruded as solid rounds at 400°C in a 500 ton vertical extrusion press at 10 mm/sec. Tensile tests revealed a significant increase in elongation with only a small Ce addition of 0.2%. The addition of cerium caused a decrease in yield strength and an increase in work hardening delaying the onset of instability. EBSD analysis shows that the small Ce addition markedly alters the texture of the extruded rods during recrystallization, and orients the c-axes of the grains at an angle to the extrusion axis whereas they are mostly normal to the extrusion axis in Mg. This reorientation favors basal slip activity leading to higher elongation. While Mg deforms mainly by twinning and fracture initiates due to voids nucleating at twin intersections, the Mg-0.2Ce alloy shows void nucleation along nonintersecting shear bands parallel to the tensile axis. The results of this study point to a design approach that combines alloying and processing to alter the slip distribution which can enhance the formability of Mg alloys.