Investigation on formability and mechanism in laser shock hydraulic warm free-bulging of AZ31B magnesium alloy foils

This paper proposes a novel dynamic impulse forming technology, that is, laser shock hydraulic warm free-bulging. This technology is especially suitable for low-plasticity but temperature-sensitive metal materials. Laser shock hydraulic warm free-bulging can tremendously increase the formability of materials and is often used in sheet metal forming fields. Thus, this technology expends the application area of laser shock liquid forming. In this study, AZ31B magnesium alloy foils with a thickness of 90 μm were investigated in room temperature to 393 K and in the laser energy range of 450–810 mJ. Maximal forming heights were obtained at different temperatures. Results showed that the maximal forming height of AZ31B magnesium alloy improved markedly as the temperature increased. Furthermore, the free-bulging height reached the maximum of 324.4 μm at 363 K. The height increased approximately 18% compared with that at room temperature. When the temperature exceeded 363 K, the maximal forming height decreased. Then, the microhardness and thinning ratio of the formed parts were investigated. At 363 K, the thinning ratio was also the largest, while the formed parts maintained a fine microhardness. Finally, through electron backscattered diffraction (EBSD) technology, the dynamic recrystallisation mechanisms and texture evolution of the formed parts at different temperatures were investigated to determine for the deformation mechanism at various temperatures. At 363 K, many fine grains and twins were obtained, improving the formability. Meanwhile, the dislocation density increased and became more uniform as the temperature increased and reached a peak at 363 K, resulting in maximal microhardness.