Surface integrity of 2A70 aluminum alloy processed by laser-induced peening and cavitation bubbles

Abstract

This paper presents a novel compound strengthening method based on laser-induced peening and cavitation peening (LIPCP). 2A70 aluminum alloy was strengthened by plasma shock wave and cavitation bubble collapse shock wave. The dynamic characteristic of cavitation bubble was captured by using a high-speed camera, and the strengthening mechanism of LIPCP was detailed elaborated. The peening depth was measured by an ultra-depth-of-field microscope and increases with increasing laser energies. But the surface roughness decreases with an increase in laser energies. The surface, after the compound strengthening, improved considerably with the laser energy and impact times, and has higher compressive residual stress. However, the compressive residual stress reaches a saturation value in the first 5 impacts due to the formation of a hardened layer on the material surface. In addition, ultrasonic cavitation erosion experiments were performed in 3.5% NaCl solution at room temperature. The results reveal that there are four typical cavitation erosion periods during the cavitation erosion process, and the mass loss rate of the treated specimen is relatively lower than that of the untreated specimen. The microscopic morphology analysis shows that there are large smooth areas on the LIPCP treated surface after ultrasonic cavitation erosion, which indicates that the fatigue life and cavitation resistance of 2A70 alloy aluminum has been greatly improved. The LIPCP provides a promising method to strengthen the hydraulic machinery beneath the water. Keywords: Hardening surface material, Coating, Plasma shock wave, Bubble collapse shock wave, Ultrasonic cavitation erosion