Optimization of multiple laser shock peening on high-cycle fatigue performance of aluminized AISI 321 stainless steel

•Multiple Laser shock peening (LSP) was carried on aluminized 321 stainless steel.•Fatigue lives of aluminized steel increase within LSP times ranging from 0 to 3.•Thermal effect in 4th LSP release compressive residual stress and produce σ phase.•A dramatic degradation in fatigue life is noticed after the 4th LSP cycle.•Potential de-twinning mechanisms during cyclic deformation are also discussed. Herein, the effect of multiple laser shock peening (LSP) on fatigue performance of aluminized steel and de-twinning behavior during cyclic deformation are investigated. Results reveal their fatigue lives successively increase within LSP times ranging from 0 to 3. Instead, life degradation is noticed after 4th LSP due to damaged adsorption layer. Consequently, the negative thermal ablations release compressive residual stress and form σ phase, accelerating crack propagation. Thus, triple LSP impacts are determined as optimal condition for fatigue resistance of aluminized steel. According to twinning dislocation initiations and glide directions, the underlying de-twinning mechanisms during cyclic deformation are also discussed.