This study presents the influence of surface mechanical pre-treatments of aviation grade aluminum alloy (2024-T3) sheets covered with three different paint systems on the laser cleaning process. Laser processing was proposed as an alternative approach for commonly used mechano-chemical methods to improve the efficiency of paint stripping and to reduce the maintenance cost of existing aircraft skins. Pre-treatments were performed in order to matt the surface and to mimic the process of deterioration of the paint coating during aircraft operation. In this work aluminum sheets were pretreated using shot peening and grinding prior to the IR-laser cleaning process. Shot peening process was performed using SiO2 shot with two different fractions (100 μm and 200 μm) with variable pressure (0.3 MPa and 0.5 MPa). Grinding was implemented using 320 grit sandpaper in dry conditions. After that a SPI20W laser with wavelength of 1064 nm, laser scanning speed of 300 mm/s, distance between passes of 40 μm and different number of passes was applied to remove a variety of painting systems from the untouched and pre-treated aluminum samples. The effect of laser cleaning process on aluminum substrate was investigated using complementary techniques such as optical microscopy, optical profilometry and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) system to perform chemical analysis.
Our previous studies showed that the effectiveness of the laser cleaning of polymeric paints strongly depends on the total thickness of the coatings and the structure of individual coating layers. In this study our results showed that the pre-treatments did not reduce the efficiency of laser stripping and did not affect any key properties of aircraft skins. IR-laser processing led only to a slight remelting and texturing of the CLAD surface but without change in overall CLAD thickness. After coatings being removed, surface of the aluminum sheets could be directly and immediately re-painted without any additional preparation.