Microstructure Analysis and Corrosion Study of Excimer Laser Modified AA2024-T351

Laser surface melting (LSM), using an excimer laser, has been employed to modify the near-surface microstructure of AA2024-T351 aluminium alloy. The microstructure and associated phases in the modified surface structure were analyzed by scanning, transmission electron microscopy and X-ray diffraction. The corrosion behavior was evelauted in the ASTM G34-01 EXCO test and by electrochemical polarization. LSM produced a thin, relatively uniform, melted layer relative to the unmelted substrate, leading to significant decrease in anodic and cathodic activities. The decrease of reactivity related mainly to the elimination of fine Al2CuMg dispersoids of the original alloy matrix within the melted layer. However, delamination of the laser melted layer from the underlying substrate was observed after the EXCO immersion test, which may be attributed to the formation of copper-rich bands at the melted layer/bulk alloy interface and the introduction of tensile residual stress in the melted region as a result of the LSM.