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 H 2SO4 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 ©2010 John Wiley & Sons, Ltd.