Laser shock peening regulating aluminum alloy surface residual stresses for enhancing the mechanical properties: Roles of shock number and energy

Abstract

The enhancement of the mechanical performance of materials is a continuous pursuit in engineering. Laser shock peening (LSP) is an advanced manufacturing method employing extreme conditions, which effectively improves the mechanical properties of the material surface. Herein, LSP was used to treat aircraft 5A06 aluminum alloy, leading to significant enhancement of properties. In the LSP process, the pulse shock wave caused severe plastic deformation of the metal surface, where the strain rate reached 107 s−1. The dislocations multiplied in large numbers and then evolved into large-angle grain boundaries and other structures to achieve grain refinement. Also, LSP significantly improved the residual stress of metals, causing a series of mechanical improvement effects. Under the impact of fine-grain strengthening, the resultant 5A06 aluminum alloy's micro-hardness was increased to 140 HV, a value 65% higher than that of bare aluminum. After the LSP process, the maximum plastic deformation layer depth (PDLD) reached 800 μm. On this basis, the ultimate tensile strength of aluminum alloy was increased by 27%, and the ultimate tensile displacement was also increased. The LSP treatment increased the strength of aluminum alloy without losing ductility. The resultant sample's friction coefficient was reduced by 34%, and the overall surface-displayed uniform wear. This work reveals the structure-activity relationships between the surface residual stress and metal mechanical properties and clarifies the LSP process's strengthening mechanism.