Microstructure Correlation with Formability for Biaxial Stretching of Magnesium Alloy AZ31B at Mildly Elevated Temperatures

Magnesium AZ31B sheets of 2 mm thickness were stretch formed with a 101.6-mm-diameter punch at temperatures from 25°C to 150°C, in 25°C increments. Surface strains were measured with a digital image correlation method. The punch height versus load curve was found to be the same for temperatures of 25°C and for 50°C, whereas at 75°C and above, the load for a given punch height started to decrease, indicating a potential change in deformation mechanism. Electron backscatter diffraction was used to quantify features of the microstructure in the tested specimens. In particular, the gradual decrease in twinning activity as a result of easier thermally activated slip with increasing temperatures is quantified across this range. Moreover, twin activity was found to predominantly involve the formation of 101¯1$$ \left\{{10\bar{1}1} \right\} $$ compression twins that rapidly transform to create secondary twins for easier strain accommodation.