Evaluation of the effects of a combined severe plastic deformation method on the hot deformation behavior of Mg-3Al-1Zn magnesium alloy

The main goal of this study is achieving thin-walled AZ31 magnesium alloy tubes with high ductility at elevated temperature. For this purpose, a combined severe plastic deformation method, including parallel tubular channel angular pressing (PTCAP) and tube backward extrusion (TBE) was used. First, PTCAP process was applied on tubular samples at 300°C and then, TBE process was performed at 300°C. After PTCAP, a necklace like microstructure, large gains surrounded by a large number of tiny recrystallized ones, was observed and the average grain size of the material decreased from 520 µm to 11.1 µm. At the next stage, After TBE, an ultra-fine grain microstructure with an average grain size of 8.6 µm was formed. After performing this combined method, the hardness value of the PTCAP and TBE processed sample increased from 37 HV to 69 HV. Hot tensile testing studies at 300°C revealed an elongation to failure value of 181% for the PTCAP and TBE processed sample, while this value for as-received sample was 55%. Fractographic SEM images showed that predominately ductile fracture was occurred in all hot tensile specimens due to nucleation of microvoids and their subsequent growth and coalescence with each other.