Effects of strain rate on mechanical properties and failure mechanism of structural Al-Mg alloys

The effects of strain rate on the mechanical properties and failure mechanism of AA5754 and AA5182 sheets were investigated. Tensile tests were conducted at quasi-static (less than 10−1 s−1) and dynamic (600, 1100 and 1500 s−1) strain rates at room and elevated temperature using an INSTRON machine and Tensile Split Hopkinson Bar (TSHB) apparatus, respectively. Shear band decoration, interrupted tensile tests, electron microscopy, and image analysis techniques were also utilized. The results obtained show that the studied alloys exhibit negative strain rate sensitivity at quasi-static rates, but mild positive sensitivity at dynamic rates. Different failure mechanisms were also observed. Strain localization and shear band formation was found to be a necessary pre-requisite for the development of damage and final failure under quasi-static conditions. In the dynamic strain rate regime however, less shear banding was observed. Void nucleation, growth and coalescence that is characteristic of dynamic tensile fracture appears to be the dominant mode for failure under dynamic conditions.