Deformation and fracture mechanisms in WE43 magnesium-rare earth alloy fabricated by direct-chill casting and rolling

Abstract

This paper examines deformation behavior of WE43 alloy in direct-chill as-cast (as-cast-WE43) and rolled heat-treated T6 (WE43-T6) conditions with an emphasis on fracture mechanisms. Unlike many Mg allows, as-cast-WE43 and WE43-T6 exhibit no tension/compression asymmetry in their yield stress. WE43-T6 material shows more anisotropy in yield stress than as-cast-WE43, which is attributed to their respected initial crystallographic textures. Both WE43-T6 and as-cast-WE43 exhibit some anisotropy in strain hardening due to texture evolution and deformation twinning. Both materials show a small elongation to fracture of approximately 6% in tension. In contrast, strain to fracture in compression is large. Crystallographic texture evolves substantially in compression, where crystals are slowly reorienting their crystallographic c-axis parallel to the loading direction with plastic strain. Both materials fracture by a typical shear fracture in compression. Fractographic analysis of fractured surfaces in compression for WE43-T6 reveals evidence of transgranular facets that are much larger than grain size with minor content of microvoid coalescence. Although elongation to fracture in tension is small with no necking, detailed analysis of fracture surfaces reveals evidence of ductile microvoid coalescence. However, the intergranular fracture character, especially in the central high stress triaxiality region of the samples, limits the ductility of the material.