Mechanical properties and formability of AZ31 magnesium alloy sheet produced by asymmetric rolling with thrust force

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Magnesium alloys have the lowest density among metals in practical use and have properties such as high specific strength and good vibration damping. However, there has been little use of these materials in metal forming because of their poor plastic deformability at normal temperature and high cost of production. To promote sheet products manufactured by metal forming, rolling technologies enabling the production of thin sheets with good surface qualities, mechanical properties and sheet formability at normal temperature are strongly required. In this study, rolling experiments using cone-shaped rolls are conducted to investigate the effects of asymmetric rolling and the thrust force on the mechanical properties and sheet formability of AZ31 magnesium. Hot-rolled AZ31 magnesium sheets were experimentally warm-rolled and reduced a thickness from 2.5 mm to 0.6 mm (a total reduction of 76%) by 11 passes at a sheet temperature of 573 K and roll temperatures of 353 K. Rolling force and axial force were measured. The grain structures and orientations of the rolled materials were also examined. Their mechanical properties such as tensile strength, 0.2% proof stress, total elongation and Lankford value (r-value) were measured by tensile tests. To investigate the sheet formability at normal temperature, conical cup tests were conducted and the sheet formability by asymmetric rolling were compared with that by symmetric rolling. The material rolled by asymmetric rolling exhibits greater elongation than that rolled by symmetric rolling. Asymmetric rolling can improve the sheet formability. However, magnesium alloys rolled by asymmetric rolling have poor sheet formability compared with mild steel sheet.