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 s(-1)) under tension and compression; and three-point bending (flexure) tests using suitable fixtures at crosshead speeds (1-100 mm/min) for varying span lengths (80-160 mm) and orientations (flat and transverse) at room temperature, 25 degrees C. The thermal and fracture behaviors of the alloy at various temperatures (25 degrees C, 100 degrees C, 150 degrees C, and 200 degrees C) are studied under quasi-static tension (0.001 s(-1)). The heating rate of the tensile specimens is 20 degrees C/min and the soaking time is 15 min. Dynamic tensile (850-1,400 s(-1)) and compressive (1,900-3,300 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. (C) 2020 American Society of Civil Engineers.

Automated summary

This study investigates the flow stress behavior, thermal and fracture behavior, as well as the performance and reliability of AZ81 magnesium alloy under different loading conditions. It also examines the effects of specimen geometry on flow stress, ductility, toughness, and energy dissipation capacity of the alloy, and discusses the applicability of existing models in various loading conditions.