Chemical Etching for Boosting Adhesive Bond Strength of CFRP–Al Joints: A Lap Shear Tensile Test Study

Carbon fiber–reinforced polymers (CFRPs) have gained widespread use across the aerospace, automotive, and energy sectors due to their high strength-to-weight ratio. Many structural applications require joining CFRPs to aluminium alloys, with adhesive bonding offering several advantages over mechanical joining methods, including uniform stress distribution and compatibility with CFRPs. Among various strategies to improve bond strength, surface preparation plays a critical role. This study investigates the effect of chemical etching on CFRP using sulfuric acid solution to enhance bond strength in single-lap joints with aluminium alloys when tested in lap shear test. Experimental results show that optimised chemical etching can triple the lap shear strength compared with untreated samples. Acid concentration significantly influences joint performance; furthermore, the soaking method of etching can yield stronger bonds than the pipette method. Additionally, chemically etched CFRP–Al joints can outperform those treated with conventional sandpaper abrasion. These findings demonstrate the effectiveness of controlled chemical etching in improving the structural integrity of CFRP–metal adhesive joints and provide insights for designing more robust hybrid structures for lightweight applications.