Contact angle and wettability of hybrid surface-treated metal adherends

Adhesion performance of adhesively bonded metal joints with aluminum and stainless steel was much dependent on the surface treatment of the adherends. This work was aimed at optimizing hybrid surface treatments to improve wettability of metal surfaces and strength of adhesive metal joints, which was a combination of mechanical, chemical, and energetic surface treatment methods. The surface free energies and wettability of hybrid surface-treated metal adherends were measured for different treatment conditions with abrasion, grit blast, sulfuric acid etching, phosphoric acid anodizing, silane treatment, plasma treatment, and flame treatment. The surface morphology and chemical composition of the metal adherends were investigated by scanning electron microscopy and X-ray photoelectron spectroscopy and the bond strengths of the single-lap joints composed of aluminum and stainless steel adherends were measured with respect to hybrid surface treatment conditions. From the experiments, an effective hybrid surface treatment condition was suggested for metal surfaces with super-hydrophilic characteristics. Also, the failure mode of adhesive metal joints was evaluated by photo-surface analysis method.