Dynamic plasticity of AZ31 magnesium alloy: Experimental investigation and constitutive modeling

This paper investigates the mechanisms of plastic deformation in magnesium alloys, both experimentally and theoretically. The focus of the study is to understand the dynamic response and microstructural evolution of AZ31 magnesium alloy under very high strain rates. Both the dynamic and quasi-static compressive tests were carried out in conjunction with the microstructural observations on the texture-eliminated AZ31 samples deformed under different loading conditions, to reveal the relation between the properties and microstructure of the material during plastic deformation. It was found that under quasi-static loading, deformation twinning/untwinning plays a key role in the plastic deformation of this alloy at medium high temperature, while at high strain rates, grain refinement due to dynamic recrystallization becomes the most important factor. A unified macro-microscopic constitutive model was then physically established to describe the thermo-viscoplastic flow behavior of the hcp materials in a broad range of coupled strain rates (0.001/s-21,000/s) and temperatures (77-523 K). It was concluded that the predictions by the unified model are in agreement with the experimental results and the model has a good effectiveness under both quasi-static and very high strain rates compared with other one-fold models. Especially, the new model can depict well the upturn phenomenon in the flow stress of the material at high strain rates.