Multifunction cavitation technology to improve the surface function of Al – Cu alloy

Abstract

Multifunction cavitation (MFC) combines ultrasonic cavitation technology and water jet peening (WJP) technology. In this processing technique, it has been reported that the residual stress necessary for improving the fatigue strength on the pure Al surface is large, whereas the amount of surface scraping by this processing is small. Moreover, improvement of the corrosion resistance of the surface of Al–Cu alloys has been reported. In this study, to improve the efficiency and accuracy of MFC technology, the dependence of the surface condition, residual stress, and surface roughness on the distance from the water jet nozzle (standoff distance) to the specimen surface were evaluated. When Al–Cu alloy specimens were processed by MFC with a swirl flow nozzle (SFN–MFC), WJP with an SFN (SFN–WJP), and conventional WJP, erosion at the center of the specimens occurred when the standoff distance was 45 mm and was reduced as the standoff distance was increased. The maximum compressive residual stress was reached at standoff distances of 55, 65, and 45 mm for SFN–MFC, SFN–WJP, and WJP, respectively. The residual stress was found to be correlated with voids formed by cavitation processing. In SFN–MFC, at standoff distances of 55 and 60 mm, the cavitation bubbles were in the high-pressure and high-temperature regimes, respectively. These results demonstrate that high-temperature and high-pressure regimes exist in MFC, unlike in conventional WJP technology, and the temperature and pressure in the cavitation bubbles depend on the standoff distance. Keywords: Multifunction cavitation, Residual stress, Surface potential, Water jet peening, Erosion trace, Standoff distance