Laser-based surface engineering to enhance adhesive bonding of aerospace aluminum 7075–T300 CFRP joints under static loading conditions

Hybrid structures combining AA7075 aluminum alloy with carbon fiber-reinforced polymers are attractive for aerospace applications, yet adhesive bonding of these dissimilar materials remains challenging due to incompatible surface chemistries and the presence of weak boundary layers on both substrates. This study investigates whether independently optimized laser treatments applied to each adherend produce stronger joints than individual surface treatments. Single-lap shear joints were prepared using a pulsed fiber laser 30 W to texture AA7075 surfaces and selectively remove the superficial resin layer from CFRP T300. Five treatment combinations were tested and evaluated through mechanical testing and failure surface analysis. The synergistic combination of aluminum texturing with high-energy CFRP cleaning increased shear strength by 39% to 17.4 ± 1.6 MPa and energy absorption by 121% to 7.5 ± 1.1 J relative to untreated joints. Failure analysis revealed a transition from dual interfacial adhesive failure to interlaminar cohesive failure involving fiber extraction, attributed to simultaneous activation of mechanical interlocking at the aluminum surface and an adhesive substitution mechanism at the CFRP surface. Neither treatment alone produced improvement. These findings establish critical processing thresholds for each substrate and identify adhesive substitution as the governing mechanism for CFRP surface optimization in hybrid adhesive joints.