Comparison of microstructure and texture in pure magnesium sheets produced by hot rolling and a new SPD process; the high-pressure compressive reciprocating shear

Poor room temperature ductility limits the usage of magnesium in engineering applications. Enhancement in these properties can be achieved through Severe Plastic Deformation (SPD). However, the samples produced by most SPD processes have limited sizes. To address this, a new SPD process, High-Pressure Compressive Reciprocating Shear (HPCRS) is proposed. HPCRS is a modified version of HPCS (High-Pressure Compressive Shearing), established by Toth et al. in Materials Characterization 154 (2019). In HPCRS, deformation occurs in a combined stress state with cyclically reversed shear. To study the evolution of microstructure and texture with strain, pure magnesium sheets with 5 mm thickness were deformed by HPCRS in a single step, at 20 Hz frequency to different thicknesses (3.5 mm- 0.94 mm), imposing strains up to ~40. The high strain rates during HPCRS generated temperatures up to 186 °C without applying external heating. The microstructure, texture, and properties of sheets produced by HPCRS were compared with the same thickness sheets made by conventional hot rolling. In the 3.5 mm thick HPCRS sample extensive twinning was observed. With increasing reduction, onset of grain refinement through dynamic recrystallization was seen. Finally, fully recrystallized microstructures with an average grain size of 1.5 μm were achieved. An off - basal spread texture at small strains developed into the ideal B-fiber shear texture at large strains. The HPCRS-processed sample exhibited superior strength and ductility compared to the hot-rolled samples. Owing to plastic deformation induced self-heating and single-step large strain capability, HPCRS overcomes conventional rolling limits and offers a scalable industrial alternative. • The new HPCRS process was applied for producing Mg UFG sheet metal in a single step. • Equivalent von Mises strain of ~ 40 was achieved at room temperature in 8 s. • Grain size was refined from ~ 140 μm to ~ 1.5 μm . • Strength and ductility were higher by 38 % and 160 % compared to hot rolled sample. • Compression, double and tensile twins were analyzed in the texture and microstructure.