Laser surface treatment to enhance the adhesive bonding between steel and CFRP: Effect of laser spot overlapping and pulse fluence


Adhesive bonding is widely applied in joining between steel and carbon fiber reinforced plastics (CFRP), while the surface characteristics of steel have a significant effect on the joint strength. To improve the adhesive bonding between DP590 steel and CFRP, surface modifications of steel by laser surface treatment with different overlap rate of laser spot and pulse fluence were applied and investigated. The evolution of surface morphology, contact angle, surface energy, and surface chemical composition of DP590 steel after laser treatment with different parameters were also studied. The results showed that surface roughness, surface energy and polar component of surface energy after treatments were closely related to the interfacial bonding strength between steel and adhesives. Specifically, higher pulse fluence can increase the surface roughness of the steel, which reduced the contact angle and improve the surface energy, thus not only leading to a better mechanical interlocking effect, but also improving the surface wettability of the adhesive to the steel surface. When there was 50 % overlapping of the laser spots, the surface wettability was further improved. In addition, the strengths of steel-CFRP joints obtained with both epoxy adhesive E-120HP and polyurethane adhesive PU6700 were significantly enhanced by laser surface treatment. Especially for the joints bonded with E-120HP, which is a high-strength and poor-toughness adhesive, the shear strength can be increased by 299 %, from 4.10 ± 0.17 MPa to 16.35 ± 0.89 MPa after laser treatment. More importantly, the adhesive failure along steel-adhesive interface was entirely avoided. This study provides both technical and theoretical guidance of laser surface treatment for fabricating high-performance metal-polymer hybrid structures by adhesive bonding.
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