Improvement in mechanical properties of extruded Mg alloy through shape control of extrusion billet

Abstract

This study proposes controlling the billet shape to enhance dynamic recrystallization (DRX) behavior and improve the mechanical properties of AZ31 alloy extrudates. Billets with two shapes—conventional cylindrical (non-tapered) and cone-shaped (tapered)—were used to compare DRX behavior and mechanical properties of the extrudates. The results indicate that the greater and more uniform deformation induced by compressive stress between the container wall and the tapered billet results in greater amounts of geometrically necessary dislocations (GNDs) and deformation twins at the beginning of the extrusion. These crystallographic features, along with a higher deformation degree, increase the DRX fraction from 81% for the non-tapered extrudate to 89% for the tapered extrudate. Consequently, the tapered extrudate exhibits a simultaneous improvement in yield strength (168–184 MPa) and elongation (25%–29%) compared to the non-tapered extrudate. Grain size reduction, texture weakening, and strain hardening by residual strain in unDRXed grains contribute to the improvement in mechanical properties of the tapered extrudate. The proposed tapered billet extrusion process offers a pathway to producing high-performance Mg alloy extrudates without additional processes such as pre-deformation or die-angle utilization.

Keywords

• Magnesium alloy
• Extrusion
• Billet shape
• Microstructure
• Tensile properties