Bonding Strength of the CFRP and AA6061 Joint Using Ascorbic Acid and Sodium Chloride Surface Treatment

The adhesive bonding of aluminum with other materials is widely used in the aerospace, marine, automotive and railroad industries that require lightweight materials. Adhesive bonding has the advantages of reduced corrosion, stress concentration, and cost effectiveness. To improve bonding strength and performance, we examined the use of ascorbic acid (vitamin C), which is a water-soluble compound and a natural reducing agent. Owing to its reducing power and acidity, ascorbic acid allows the Al etching process to proceed efficiently to increase the surface roughness and prevent Al oxidation. In addition, this study used an eco-friendly technique of simply immersing aluminum substrates in an ascorbic acid solution with sodium chloride. The surface free energy was evaluated using the sessile drop method and calculated using the Owens–Wendt–Rabel and Kaelble method. Confocal microscope was used to investigate the roughness of the surface, and the functional groups of Al surface were analyzed by X-ray photoelectron spectroscopy. The bonding strength was measured using the single-lap joint shear test. Compared to aluminum without treatment, the bonding strength of a treated AA 6061 was enhanced by 58.6%.