Warm Forming Response of ZEK100 Sheet obtained under Biaxial Stretching with Full-Field Displacement Measurements

Abstract

The warm forming response of ZEK100 sheet was studied between 150 °C and 250 °C using hydrostatic bulging coupled with full-field displacement mapping. Due to the strain-rate sensitivity of magnesium alloys at elevated temperature, it was important to ensure that the strain-rate remained reasonably constant during the bulge test. Various gas pressure versus time profiles were used to achieve strain-rates in the range of 0.01 s−1 to 0.1 s−1. The results from equi-biaxial bulge testing will be detailed in addition to bulge testing performed using elliptical dies with various aspect ratios to generate data under different biaxial stretching conditions. Supplementary characterization was provided using shear specimen data and tension test data from the rolling and transverse directions of the sheet. The biaxial, tensile, and shear data was used to calibrate a linear transformation-based anisotropic yield function at 200 °C. The yield function coefficients were optimized by matching the surface displacement data between experiments and finite element simulations of the bulge test. Agreement of the surface displacement data for a given applied pressure ensured that both the stress and strain in the bulged dome were accurately captured. Finite element simulations of the bulge tests were compared to experimental data to confirm accuracy of the calculated yield function.