Flow Stress Behavior of AZ81 Magnesium Alloy under Dynamic Loads

The performance of a structure depends on its material characteristics under various conditions of loadings, strain rate, and temperature, and therefore, it is necessary to understand these characteristics properly for the safe and reliable design of structures. In this paper, the flow stress behavior of AZ81 magnesium alloy is determined under tensile, compressive, and flexural loads at different strain rates and temperatures. An electromechanical universal testing machine of capacity 250 kN is used to perform quasi-static tests (${0.0001–0.1\mathrm{s}}^{-1}$) under tension and compression; and three-point bending (flexure) tests using suitable fixtures at crosshead speeds ($1–100\mathrm{mm}/\min$) for varying span lengths ($80–160\mathrm{mm}$) and orientations (flat and transverse) at room temperature, 25°C. The thermal and fracture behaviors of the alloy at various temperatures (25°C, 100°C, 150°C, and 200°C) are studied under quasi-static tension (${0.001\mathrm{s}}^{-1}$). The heating rate of the tensile specimens is $20°\mathrm{C}/\min$ and the soaking time is $15\min$. Dynamic tensile (${850–\mathrm{1,400}\mathrm{s}}^{-1}$) and compressive (${\mathrm{1,900}–\mathrm{3,300}\mathrm{s}}^{-1}$) experiments are conducted using appropriate arrangements of Hopkinson bar systems. The effects of specimen geometry on the flow stress of the alloy are observed under compression. Ductility and toughness are determined to establish the energy dissipation capacity of the alloy. Fractographs of the fractured tensile specimens are studied by scanning electron microscope (SEM). Also, the applicability of the existing Cowper–Symonds and Johnson–Cook models in the aforementioned loading conditions is discussed.