Dual protection against electrochemical corrosion for AA5083 Al alloys: Synergistic action of superhydrophobicity and strain-strengthening

Abstract

A new laser compound process, namely, laser shock peening of the surface to obtain the strain-strengthening layer (under the ultrahigh strain rates of >107 s−1), followed by laser surface texturing to achieve the superhydrophobicity on the strengthened surface, is proposed to provide dual protection against electrochemical corrosion for AA5083 Al alloys. The surface morphology, microstructure, residual stress and surface wettability of AA5083 Al alloy after laser compound processing were investigated. The corrosion experiments were performed by an electrochemical station. Results indicate that LSP-induced strain-strengthening layer with grain refinement and high-density dislocations accompanied by compressive residual stress on the surface. Subsequent LST produced surface superhydrophobic structures with an SCA of 155.95°. The electrochemical corrosion experiments displayed that the superhydrophobic surface works as the first protection to prevent the corrosive medium from adsorbing. With the failure of the defense function of superhydrophobic structures, the following refined grains and high-density dislocations in the strain-strengthening layer are preferred to generate protective passive films. Besides, compressive residual stress retards the permeation of Cl− anions, greatly delaying the breakdown of passive films. For the Al alloy immersed in 3.5 % NaCl solution for 48 h, the LSP-LST specimen exhibited the lowest Icorr and the highest Ecorr and Epit, with the value of −1.304 V, −0.662 V, and 50.71 μA/cm2, which exhibited the greatest corrosion properties.