Impact of laser shock peening on high-strength aluminum alloys in marine environments

High-strength aluminum alloys employed on offshore platforms endure exposure to complex and severe environmental conditions. Welding detrimentally impacts the heat-affected zone (HAZ), causing a notable deterioration in mechanical properties, which poses significant risks to platform integrity. This study aims to address these challenges by evaluating the efficacy of laser shock penning (LSP) in enhancing the mechanical performance and fatigue life of two aluminum alloys, 6061-T6 and 6082-T6. LSP induces high strain-rate plastic deformation, resulting in dense dislocation structures and promoting grain refinement mechanisms within the microstructure. A comparative analysis of LSP treatments using laser pulse energies of 1.8 J and 2.6 J reveals that the 1.8 J pulse energy optimally enhances mechanical properties and fatigue resistance. Specifically, LSP generates hardened layers with depths of 1.5 mm and 0.8 mm on the surfaces of the base material (BM) and HAZ, respectively, through plastic deformation-induced strengthening. Post-LSP treatment at 1.8 J, the surface hardness of the HAZ increased by 12.3 % and 40.3 % for 6061-T6 and 6082-T6 alloys, respectively. Additionally, residual compressive stress increased by 22 MPa and 61.2 MPa, while yield strength improved by 4.6 % and 4.8 %, respectively. The fatigue life of the alloys was extended by factors of 1.9 and 2.33, respectively. Furthermore, dislocation accumulation and residual stress concentration altered the fatigue fracture mode from ductile fracture in untreated alloys to a mixed ductile and cleavage fracture mode post-LSP. These findings underscore LSP’s potential as a transformative technique for significantly improving the structural integrity and longevity of aluminum alloys in offshore applications. • Study on LSP effects on properties of 6061 and 6082 aluminum alloys and HAZ. • Characterization of hardened layer, stress, tensile, and fatigue properties under LSP. • Fatigue fracture mode shifts from ductile to mixed ductile-cleavage post-LSP. • LSP boosts fatigue life, with HAZ showing a 2.33x improvement over BM.