Non-destructive UV femtosecond laser cleaning of primer on CFRP surface

The ultraviolet (UV) femtosecond laser has both high peak energy density and short pulse width characteristics, which can minimize the thermal damage to the substrate. The primer on the Carbon fiber reinforced polymer (CFRP) substrate surface was successfully removed by UV femtosecond laser for the first time. The influence of process parameters on the cleaning effect was analyzed based on the surface morphology and verified by chemical composition changes, so a reasonable process window was determined. Furthermore, the performances of the surface with different degrees of cleaning were tested. It is found that the completely cleaned surface is more hydrophilic with improved hardness. Compared to the original substrate, the hardness increased by 165.8 %, while the contact angle decreased by 6.4 %. Finally, combining experiment and analysis, the cleaning mechanisms of primer removal were summarized, i.e., the combined effects of ablation and photochemical mechanisms. The optimal laser parameters are a scanning speed of 800 mm/s, an energy density of 1.82 J/cm², and 4 cleaning times. Under these parameters, the primer is completely removed without damaging the substrate. The damage form is the mechanical fracture of carbon fibers under the excessive cleaning condition. This paper provides a reference for the removal of primer on the surface of CFRP, therefore increasing the possibility of reusing CFRP substrate.