Microstructural evolution and mechanical properties of AZ31 Mg alloy fabricated by a novel bifurcation-equal channel angular pressing

Abstract

In this work, a novel type of short-process deformation technology of Mg alloys, bifurcation-equal channel angular pressing (B-ECAP), was proposed to refine grain and improve the basal texture. The cylindrical billets were first compressed into the die cavity, then sequentially flowed downward through a 90° corner and two 120° shear steps. The total strain of B-ECAP process could reach 3.924 in a single pass. The results of microstructure observation showed that DRX occurred at upsetting process in the die cavity and completed at position D. The grains were refined to 6.3 µm at being extruded at 300 °C and grew obviously with the extrusion temperature increase. The shear tress induced by 90° corner and two 120° shear steps resulted in the basal poles of most grains tilted to extrusion direction (ED) by ±25°. Compared with the original billets, the extruded sheets exhibited higher yield strengths (YS), which was mainly attributed to the grain refinement. The higher Schmid factor caused by ED-tilt texture resulted in a fracture elongation (FE) more than that of the original bar in ED, while was equivalent to that in transverse direction (TD). As the extrusion temperature increased, the variation of UTS and YS in ED and TD decreased gradually without ductility obviously decrease.

Keywords

AZ31 Mg alloy / B-ECAP / microstructure / texture evolution / mechanical properties

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