Non-basal texture development of an extruded Zn-Mg alloy for tuneable mechanical properties

Non-basal textures of an extruded Zn-0.4 wt%Mg alloy have developed via modifying extrusion and subsequent annealing conditions, and the texture effect on mechanical properties of this alloy has been examined in this study. Conventional and quasi-in-situ electron back-scatter diffraction (EBSD) and a technique combining transmission Kikuchi diffraction and scanning transmission electron microscopy – energy-dispersive X-ray spectroscopy have been conducted for texture characterisation. A strong < 01 1 ‾ 0 >//ED (extrusion direction) basal texture was observed after extrusion at 250 °C and 300 °C, which remained unchanged after post-extrusion annealing. In contrast, a unique non-basal texture, approximately < 2 ‾ 4 2 ‾ 1 >//ED, develops after 150 °C extrusion followed by annealing from 150 to 300 °C. The 150 °C as-extruded microstructure comprises deformed grains near < 06 6 ‾ 1 >//ED orientations and dynamically recrystallised grains with orientations spread between < 04 4 ‾ 1 > and < 2 ‾ 4 2 ‾ 1 >//ED. Post-extrusion annealing weakens the < 06 6 ‾ 1 >//ED texture while strengthening the < 2 ‾ 4 2 ‾ 1 >//ED texture. Quasi-in-situ EBSD observations of 150 °C extruded samples during 200 °C annealing reveal that the texture modification initiates with the growth of recrystallised grains between < 04 4 ‾ 1 > and < 2 ‾ 4 2 ‾ 1 >//ED orientations by replacing the surrounding deformation grains until complete recrystallisation. Continued annealing led to the formation of a special grain boundary with 30° misorientation about < 11 2 ‾ 0 > rotation axis by impingement of two grains oriented near < 2 ‾ 4 2 ‾ 1 >//ED. The thermal stability of this boundary during annealing is attributed to Mg segregation. Non-basal textured samples exhibit enhanced ductility and strain hardening response by increasing Schmid factor for dominant slip systems.