Formability and Grain Size of AZ31 Sheet in Gas Blow Forming Process

Initial microstructural effect on mechanical properties and high temperature formability was investigated by experiments such as uniaxial tensile test at room temperature and 400 °C and biaxial gas blow forming at 400 °C. To observe distinct microstructural effect, three types of AZ31 alloy sheets which have different average grain size as 16.41 μm (type-A), 11.02 μm (type-B), and 7.58 μm (type-C) were investigated. Among the three types of AZ31 alloy sheets, Type-A and Type-B was the partially hardened specimens containing twins (AZ31-H) and Type-C was fully annealed specimen with equiaxed grains (AZ31-O). At room temperature tensile test, initial microstructural features such as twin density, dislocation density, and grain size affected mechanical properties. However at 400 °C tensile test and gas blow forming, only initial grain size affected mechanical properties due to the fact that the original microstructures of AZ31-H alloy sheets evolved into recrystallized microstructures with equiaxed grains. Accordingly, AZ31-H magnesium alloys, which have improved mechanical properties at room temperature, could not affect superplastic formability and mechanical properties of post-superplastic formed microstructures.