Strength Degradation Mechanism of CFRP and Aluminium Alloy Hybrid Bonded-Riveted Joints Under Salt Spray Environment

Hybrid bonded-riveted joint has poor corrosion resistance under salt spray environment, especially for dissimilar materials. The study investigates the strength degradation mechanism of carbon fiber reinforced polymer and aluminium alloy (CFRP-Al) hybrid bonded-riveted joints under salt spray environment, and it proposes a method to improve corrosion resistance of CFRP-Al hybrid bonded-riveted joints. The study found that the strength degradation of CFRP-Al hybrid joints under salt spray environment was mainly attributed to the decrease in bonding strength at the aluminum/adhesive interface. Comparison results further showed that the diffusion of corrosive medium along the aluminum/adhesive bonding interface caused a 33.3% decrease in joint strength, while the accelerated electrochemical corrosion of the aluminum surface caused a 59.3% decrease in joint strength. Applying laser to modify the surface characteristics of aluminum resulted in a 46% increase in the maximum shear loads of CFRP-Al hybrid bonded-riveted joints before salt spray exposure and a 45% increase after salt spray exposure. It has been found that laser surface treatment produced rough microstructures on aluminum surface, which increases the bonding area between adhesive and aluminum alloy, effectively preventing the diffusion of corrosive medium along the bonding interface. Furthermore, a dense oxide layer was formed by laser surface treatment on aluminum surface, which contributed to slow down the galvanic corrosion between CFRP and aluminum. Consequently, an apparently improvement was observed in the bearing capacity and corrosion resistance of CFRP-Al hybrid bonded-riveted joints.