Unveiling the formation of basal texture variations based on twinning and dynamic recrystallization in AZ31 magnesium alloy during extrusion

Abstract

Commercial Mg extrusions usually develop various types of basal textures, affecting the formability and mechanical properties. The mechanisms for the formation of basal texture variations were systematically investigated for the first time based on the twinning and dynamic recrystallization (DRX) during extrusion using electron back-scatter diffraction (EBSD) characterization. The results indicate that {101¯2} extension twins with various variants played a key role in the formation of [101¯0] fiber texture, while twin-induced DRX mechanism associated with {101¯1} twins made a limited contribution to overall texture evolution. The microstructure developed consecutively as a result of continuous DRX (CDRX) and discontinuous DRX (DDRX) after twinning with different nucleation of new orientations. In the unDRXed region, new DRXed grains with 30° [0001] GBs preferentially nucleated via CDRX, forming preferred selection of [21¯1¯0] fiber orientation. Consequently, [101¯0] fiber texture became weakened with [21¯1¯0] fiber component strengthening, progressively leading to the development of [101¯0]-[21¯1¯0] double fiber texture. In the DRXed region, DDRX further occurred along the serrated grain boundaries and at the triple junctions of the parent grains by bulging, forming fresh DRXed grains without preferred orientation selection. Thus, the [101¯0]-[21¯1¯0] double fiber texture became randomized and gradually transformed into non-fiber texture at the late stage of extrusion. Besides, typical nucleation sites for DRX and subsequent grain growth were also discussed in this study. These findings unveil that basal texture variations are attributed to the twinning and DRX mechanisms during extrusion, which leads to new insight to design new wrought Mg alloys with high performance by grain refinement and texture modification.