Simulation and Experimental Study on Variable-power CO2 Laser Paint Removal from Aluminum Alloy Surfaces

ZHANG Tiangang; LIU Jiabang; DING Yefeng; ZHANG Zhiqiang; XUE Peng; ZHANG Hongwei

doi:10.16490/j.cnki.issn.1001-3660.2026.08.011

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Surface Technology ›› 2026, Vol. 55 ›› Issue (8) : 138-149. DOI: 10.16490/j.cnki.issn.1001-3660.2026.08.011

Laser Surface Modification Technology

Simulation and Experimental Study on Variable-power CO₂ Laser Paint Removal from Aluminum Alloy Surfaces

ZHANG Tiangang^a, LIU Jiabang^a, DING Yefeng^a, ZHANG Zhiqiang^a, XUE Peng^b, ZHANG Hongwei^b,*

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Abstract

The maintenance and refurbishment of composite paint layers on civil aircraft skins are critical for flight safety. Traditional chemical stripping and manual grinding methods, however, are characterized by high pollution, labor intensity, and low efficiency. While laser cleaning has emerged as a promising eco-friendly alternative, widely used nanosecond pulsed fiber or Nd:YAG lasers (wavelength: 1 064 nm) often cause thermal damage to the substrate due to the high absorption rate of aluminum alloys at near-infrared wavelengths. To address this challenge, the work aims to investigate the efficacy and mechanism of removing acrylic polyurethane composite paints from LY12 aluminum alloy surfaces with a continuous-wave CO₂ laser (wavelength: 10.6 µm). The CO₂ laser is selected for its high selectivity, as organic paint layers exhibit high absorption at this wavelength, whereas the metallic substrate reflects approximately 80% of the energy, theoretically protecting the anodic oxide film.
A comprehensive methodology integrating finite element simulation (with COMSOL Multiphysics) and experimental validation was employed. Transient thermal-mechanical coupled models were established for both single-pit ablation and multi-pass area scanning under variable power conditions (10 W, 20 W, and 30 W). The simulation assumed an ideal Gaussian beam distribution and considered the temperature-dependent thermal properties of the composite paint layer (total thickness: 115 µm). Key process parameters included a scanning speed of 600 mm/s and a 90% overlap rate. Experimental validation was conducted with a T40 CO₂ laser, with surface integrity characterized via optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and white light interferometry (WLI). Additionally, high-speed ICCD imaging was utilized to capture the dynamic plume evolution to elucidate the cleaning mechanism.
Simulation results indicated that the calculated ablation crater widths were in good agreement with the experimental data, while the depth increased significantly with power. Notably, the simulation revealed that ablation did not cease immediately upon laser shut-off, and residual heat extended the material removal process by 21-48 µs. Although the calculated thermal stress at the pit center (approx. 39.8 MPa) exceeded the paint's tensile strength, the depth of removal attributed to thermal stress was less than 1.1% of the total depth, confirming that gasification ablation was the dominant mechanism.
In the multi-pass scanning experiments, the results matched well with the simulation predictions regarding the paint removal depth. At a low power of 10 W, the cleaning was incomplete; while the topcoat was removed, a residual primer layer of approximately 15 µm remained, accompanied by surface deposits of thermally stable β-copper phthalocyanine blue pigment. At a high power of 30 W, the paint was fully removed, but the excessive energy input caused the surface temperature to exceed the melting point of the anodic oxide film (reaching approx. 2 399 K in simulation), resulting in severe oxide spallation and increased surface roughness (S_a = 1.02 µm).
The optimal processing window was identified at 20 W. Under this condition, the composite paint layer was completely removed without damaging the substrate. The anodic oxide film remained intact, exhibiting only minor micro-cracks induced by thermal stress, which did not compromise the substrate's integrity. This parameter yielded the superior surface quality with the lowest roughness (S_a = 0.49 µm). Furthermore, comparative ICCD imaging revealed a distinct difference in mechanisms: unlike nanosecond lasers which generated expanding plasma shockwaves, the CO₂ laser process produced no plasma, relying solely on a coupling mechanism of dominant ablation and auxiliary thermal stress.
In conclusion, this study validates the accuracy of the developed finite element models for predicting CO₂ laser cleaning outcomes. The findings demonstrate that optimizing laser power is crucial for achieving selective paint removal, providing a theoretical and experimental foundation for the application of CO₂ lasers in high-precision aviation maintenance.

Key words

laser cleaning / CO₂ laser / aluminum alloy / acrylic polyurethane paint layer / laser power / simulation and experiment

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ZHANG Tiangang, LIU Jiabang, DING Yefeng, ZHANG Zhiqiang, XUE Peng, ZHANG Hongwei. Simulation and Experimental Study on Variable-power CO₂ Laser Paint Removal from Aluminum Alloy Surfaces[J]. Surface Technology. 2026, 55(8): 138-149

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