Laser cleaning of oxide layers on A2024 aluminum alloy using a nanosecond pulsed laser: Surface morphology and mechanism analysis

Laser cleaning provides a green and efficient method for cleaning oxide films from aluminum alloys. This study systematically investigated the surface state and chemical composition specimens after laser cleaning with different laser fluence. By combining scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), an evaluation criterion for assessing oxide film removal on aerospace aluminum alloys was established. This criterion was used to develop cleaning processes and determine cleaning and damage threshold. The optimal cleaning parameters were identified, and the underlying removal mechanisms were analyzed. The results demonstrated that at a 70% overlap rate, the cleaning threshold was measured at 3.82 J/cm². The optimum state was achieved at 7.64 J/cm², while the damage threshold was 11.46 J/cm². At the damage threshold, the surface exhibited severe melting and crack formation, leading to substrate damage. The removal mechanism was closely related to laser fluence (F). At lower laser fluences, the dominant mechanism was likely associated with laser-induced phase explosion. As the fluences increased, the mechanism transitioned to predominantly laser ablation. At even higher laser fluences (F), laser-induced evaporation became predominant. This study may provide valuable insights for the application of laser cleaning in the pre-weld treatment of aerospace aluminum alloys.