The effect of laser scanning direction on the bonding properties of unidirectional CFRP

Abstract

Laser surface treatment presents a promising method for high-quality pretreatment of CFRP prior to adhesive bonding, owing to its advantages in precision, efficiency, and controllable processing quality. However, the complex heat transfer behavior resulting from the disparity between axial and radial thermal conductivities of carbon fibers poses significant technical challenges in achieving high-quality bonded joints. This study examines the effects of anisotropic heat transfer and thermal accumulation induced by the angle between the laser scanning path and fiber orientation, as well as by scanning speed, on the surface morphology, physicochemical properties, mechanical performance, and failure modes of laser-treated CFRP. The results reveal that optimized parameters, specifically a 45° scanning direction and a scanning speed of 3000 mm/s, effectively remove resin while preventing carbon fiber damage. This preserves the structural integrity of unidirectional CFRP and produces surface textures with distinct fiber exposure and consistent alignment. The treated surfaces exhibit improved wettability and achieve a maximum tensile shear strength of 17.25 MPa, which is 61.82% to 96.12% higher than that obtained under other processing conditions—with cohesive failure as the predominant failure mode. These findings offer new insights into the control of thermal effects during the laser processing of anisotropic materials.