Performance of Al alloys following excimer LSM—anodising approaches

The potential application of laser surface melting (LSM) as a pre‐treatment prior to conventional anodising in sulfuric acid electrolyte has been evaluated. For this purpose, AA2050‐T8 (Al? Cu? Li) and AA2024‐T351 (Al? Cu? Mg) aerospace alloys were compared. For LSM, a KrF excimer laser (248 nm) was used, with variation of the number of pulses received per unit area. After LSM, the specimens were anodised at a constant voltage of 12 V in 0.46 M H₂SO₄ for different times from 4 to 20 min, followed by sealing in boiling water for 30 min. Material characterisation, in terms of surface morphology, microstructural and laser‐induced phase transformations, was performed using scanning and transmission electron microscopies (TEMs). The corrosion behaviour was evaluated using the ASTM G34‐01 EXCO test at 25 °C for 6 h. The results showed that excimer LSM, used as a pre‐treatment prior to anodising, greatly improved the anodising performance, through the dissolution of intermetallic phases in the near‐surface alloy. Further, different exfoliation susceptibility was observed by comparing both alloys, being strongly dependent on the presence and distribution of the main constituent phases, e.g. T₁ (Al₂CuLi) and S (Al₂CuMg) phases, for AA2050‐T8 and AA2024‐T351, respectively. Copyright © 2009 John Wiley & Sons, Ltd.