Tensile properties, residual stress distribution and grain arrangement as a function of sheet thickness of Mg–Al–Mn alloy subjected to two-sided and simultaneous LSP impacts

•Stress distribution and grain arrangement as a function of thickness are analyzed.•UTS and elongation of TSLSPed sheet are strongly dependent of sheet thickness.•Influence process of sheet thickness on tensile properties of Mg–Al–Mn alloy is presented.•Optimal thickness of Mg–Al–Mn alloy sheet is determined in the present work.•Thin sheet shows poor properties due to coupling effect of two opposite shock waves. Two-sided and simultaneous laser shock peening impacts is considered as a novel surface treatment technology for the turbine blade and thin-walled component. In this paper, tensile properties of Mg–Al–Mn alloy specimens with different sheet thickness under two kinds of laser shock peening strategies were investigated, and an overlapping three-dimension axisymmetric numerical model was developed to analyze the effects of sheet thickness on residual stress distributions. Meanwhile, special attentions were paid to the in-depth microstructural evolution as a function of sheet thickness. Results showed that sheet thickness had an important influence on the tensile properties of Mg–Al–Mn alloy, and the generated residual stress distribution and grain arrangement were two important factors. The corresponding influence mechanism of sheet thickness on the tensile properties of Mg–Al–Mn alloy was also presented, and the optimal thickness of Mg–Al–Mn alloy sheet may be 4mm or more.