Corrosion performance and restoration of laser-formed metallic alloy sheets

Abstract

Previous studies of laser forming have been focused on understanding the laser forming mechanisms, investigating the effects of important laser process parameters on deformed shape, and modeling the forming process. Although microstructures and mechanical properties have received some attention, no work has addressed corrosion behavior of laser-formed components. However, laser forming is a thermal process with substantial thermal cycles required; sensitization of microstructures to corrosion may be anticipated. This paper investigates the corrosion performance of various laser-formed metallic alloy sheets, including AA 2024-T3, AA 7075-T6, and AA 5083-O aluminum alloys, and AISI 304 austenitic and AISI 430 ferritic stainless steels using various standard corrosion testing methods. The results showed that the laser forming process induced different degrees of sensitization within the irradiated zones and the heat-affected zones (HAZs), leading to significant intergranular corrosion attacks for most of the alloys. Materials characterization of the microstructural evolution, in terms of elemental segregation, precipitate distribution, and phase transformation within the laser irradiated zones and HAZs using field emission gun-scanning electron microscopy and TEM, provided evidence of an increased susceptibility to localized corrosion. However, an improved resistance to intergranular corrosion after laser forming was observed for AA 5083-O alloy. In order to restore the corrosion properties of laser-formed AA 7075-T6 components, postforming heat treatments (PFHTs), involving solution treatment at 480 °C for times of 0.5, 2, and 4 h followed by artificial aging at 120 °C for 20 h, were carried out. The results indicated that both corrosion resistance and microhardness were fully recovered to those of the original T6 condition via appropriate PFHT.