Laser Surface Melting to Mitigate Intergranular Corrosion of Sensitized AA5083

Abstract

AA5083 is a solution-strengthened, supersaturated Al-Mg alloy. It has become widely used in corrosive and harsh environments, such as marine settings, due to its exceptional corrosion resistance and impressive strength-to-weight ratio. However, when exposed to moderately elevated temperatures, the alloy undergoes a process called sensitization, resulting in the precipitation of the β phase. This intermetallic precipitate is rich in magnesium and has anodic properties, creating a microgalvanic couple with the more noble aluminum (Al) matrix. Consequently, the sensitized alloy experiences intergranular corrosion due to the anodic dissolution of the grain boundary in a corrosive environment. Various techniques for dissolving intermetallic particles into the matrix have been reported in the literature, but they are often impractical for service components, and traditional solutionizing treatments tend to decrease mechanical properties. This study aimed to investigate the impact of pulsed excimer laser irradiation, as a novel approach, on the surface morphology, chemical composition, and electrochemical behavior of highly sensitized AA5083 samples. To achieve this, various analytical techniques were used, including profilometry, optical microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, and localized potentiostat scans. The results of this investigation showed that laser surface melting (LSM) led to a reduction in the open-circuit potential and exchange current density in a 0.6 M NaCl aqueous solution, mainly due to increased surface homogenization. Furthermore, multiple grazing incident x-ray diffraction scans were performed to identify the changes in the metallurgical and crystallographic parameters in the near-surface region. Anodic polarization scans of the LSM surface galvanically coupled with a more cathodic base metal exhibited a lower corrosion current density than the theoretical value suggested by mixed potential theory. The improved performance could potentially be attributed to the surface homogenization and formation of a robust passive layer on the LSM surface.