Local mechanical behavior and enhanced ductility of ultrastrongly textured AM50 rods processed via constrained friction processing

Constrained friction processing (CFP) is an innovative technique for lightweight materials, producing fine or ultrafine microstructures through severe plastic deformation. CFP favors the formation of ultrastrong B-fiber texture in rods of Mg alloys, with its orientations varying along the rod according to the local material flow conditions. This study aims to investigate the local micromechanical behavior of AM50 rods produced via CFP and the deformation mechanisms under tensile loading specific to each analyzed position. For this purpose, a combined analysis of local microstructure and microindentation was performed, followed by tensile testing of micro-flat specimens taken at three rod positions, i.e. center and edge along the plunge direction, and middle along the radial direction, in order to investigate the role of grain size and texture on the local deformation mechanisms, and ultimately, the local mechanical properties. The results indicate that texture has a more dominant influence than grain size on the local mechanical behavior of rods processed via CFP given the pronounced gradient of ultrastrong textures observed along the rod radius, which determines the dominant deformation mechanisms. Furthermore, an approach using quasi-in-situ tensile tests performed at the center of the rod indicates that slip and tensile twinning are the main deformation modes for the ultrastrong B-fiber texture observed at this position. In contrast, at the middle of the rod, the deformation of the local ultrastrong basal texture is ruled by basal 〈a〉 slip, combined to the slip transfer. An exceptional enhancement in elongation at break (≈49 %) is observed in the sample taken at the edge of the rod, with an ultrastrong B-fiber texture tilted 25° in relation to the center. This is attributed to a combination of lattice rotation, which aligns the basal planes at 45° to the tensile axis, and the maximized activity of basal 〈a〉 slip.