Microstructure and mechanical properties of AZ31 magnesium alloy processed by multi-directional forging at different temperatures

Multi-directional forging (MDF) was carried out on AZ31 magnesium alloy up to 36 passes in the temperature range of 300 °C to 400 °C. Microstructure evolution at the center and edge regions of the specimen during the MDF process was investigated and correlated with the mechanical properties. Upon MDF, the material undergoes pronounced grain refinement but an inhomogeneous grain structure is formed due to the inhomogeneous strain distribution between the center and edge regions. After 36 passes, the microstructure at the center region is composed of finer and more homogeneous grains than that at the edge region. Tensile tests show a significant improvement of mechanical properties after MDF. With the increase of MDF passes, the yield strength both at the center and edge regions first increases and then reduces due to twin induced dynamic recrystallization. Compared to the edge region, the mechanical properties at the center region are superior and less affected by the forging temperatures after 36 passes. Among the experimental forging temperatures, 350 °C is favored to get a more uniform mechanical properties across the specimen.