Tensile characterization and constitutive modeling of AZ31B magnesium alloy sheet over wide range of strain rates and temperatures

Abstract

Magnesium alloys are an ideal candidate due to their low density in comparison to aluminum and steel alloys when designing a vehicle with lower weight and therefore, reduced fuel consumption. It is important to characterize the strain rate sensitivity of any material that will be used in a structure which can undergo high rate deformation (as in an automobile crash) as well as during high velocity forming processes such as electromagnetic or electrohydraulic forming. Tensile tests for AZ31B magnesium alloy sheet at different strain rates were carried out using different testing techniques: (i) quasi-static strain rates tests were conducted in a range between 10 −3 and 10 −1 s −1 using a conventional electro-mechanical tensile testing apparatus; (ii) intermediate strain rates tests at 4.0 × 10 1 to 10 2 s −1 using an instrumented falling weight apparatus; and (iii) high strain rates at 0.5 × 10 3 to 1.5 × 10 3 s −1 using a tensile split Hopkinson bar. Furthermore, quasi-static and high strain rate tests were also performed for different temperatures, from room temperature up to 250 °C. Strain rate and temperature effects are also discussed for rolling and transverse direction, to identify the variation of sheet properties with loading direction. Finally, the constitutive fitting of the stress–strain curves to the widely employed Johnson–Cook material model equation is evaluated and also a new model is proposed based on a modified J–C model to account for the variation of strain hardening with strain rate.