Box-Behnken optimization of the atmospheric-pressure air plasma treatment on the bonding performance of aluminum 5754 joints

This study investigated the effects of atmospheric-pressure air plasma treatment parameters on the surface properties and adhesive bonding strength of aluminum 5754 alloy single-lap joints, using Loctite 401 cyanoacrylate adhesive. A Box-Behnken design was employed to optimize plasma frequency, power, and time, focusing on their impact on surface wettability and lap-shear strength. Surface characterization was performed using contact angle measurements and X-ray Photoelectron Spectroscopy (XPS). The results showed that both contact angle and shear strength were significantly influenced by atmospheric-pressure air plasma treatment parameters of frequency, power, and time, as well as their quadratic and interaction terms. The lowest contact angle of 16.6 degrees, indicating a high wettability, was achieved at optimal parameters (1250 Hz, 200 W, 60 s) due to the removal of hydrocarbon contamination and the formation of oxygen-containing groups. Correspondingly, lap-shear strength exhibited a remarkable increase, ranging from 35% to approximately 400% compared to untreated sample. The highest shear strength of 9.345 MPa was also obtained at 1250 Hz, 200 W, and 60 s. It was observed that optimized plasma treatment changed the failure mode from adhesive to cohesive dominance, signifying improved interfacial bond strength. Higher cohesive failure ratios correlated directly with increased shear strength, indicating optimal plasma parameters create stronger, more reliable bonds. These findings underscore the efficacy of atmospheric-pressure air plasma treatment in optimizing surface properties for enhanced adhesive bonding of Al5754 alloys in demanding applications.