Constitutive description, processing maps, and un-explored deformation mechanisms of pure Mg and Mg-6Al(wt%) alloy under hot compression

Abstract

This study investigates the hot deformation behavior and final microstructure features with and without aluminum (Al) incorporation in magnesium (Mg). To this end, pure Mg and Mg-6Al(wt%) alloy were subjected to high-temperature compression and systematically analyzed the flow stress, activation energies, Zener Hollomon parameters, processing maps, and microstructure evolution, including geometrically necessary dislocations under different g vectors. These all were in an excellent relationship with each other. The microstructure analysis greatly validated the processing map parameters. Amazingly, we have attained an unexplored grain boundary sliding phenomenon under high-strain rate compression in pure Mg. This phenomenon is only reported in high-temperature tensile specimens, especially for those who attained superplasticity. Unfortunately, the mechanism attained at a strain rate (10 s−1) and temperature (573 K), which is referred to as an unstable region. Above the temperatures of 573 K, the Mg lost thermal stability, and an abrupt increase in grain size happened (3–40 µm). The addition of Al restricted the abnormal grain growth at elevated temperatures and retained grain size within < 10 µm. The higher geometrically necessary dislocation density and increase in grain boundary energy are the potential reasons for the thermal stability of Mg-Al alloy. Therefore, incorporating the Al not only enhances the formability of Mg but also provides many different stable zones, thermal stability and increases the power dissipation efficiency.