The isothermal compression experiments with the strain rates of 0.01–10 s−1 and deformation temperature range of 300–420 °C are performed to investigate the hot deformation behavior of A356 aluminum alloy. Also, the complex deformation mechanisms are analyzed. It is found that, as the strain is gradually increased, the flow stress first rises, and then the stable stress appears without a tangible peak. The microstructures exhibit large elongated grains, and only a few small new grains appear under most deformation conditions. It is because ...