Enhanced interfacial bonding strength in K-300 adhesive joint between aluminum alloy and mild steel substrates through effective resin precoating treatment

Abstract

In this work, two different surface treatments, such as grinding and acid-pickling, were applied to both mild steel and aluminum alloy substrates for performance comparison. A novel method known as resin precoating (RPC) has been used effectively to seal the micro-cavities surface and enhance substrate wetting. The RPC solution consists of 10 % resin, and 90 % acetone (without hardener) is applied onto the grinding and acid-pickling metal substrate. The acetone solution facilitates resin penetration into the micro-cavities formed through grinding and acid pickling. It enables effective coating and wetting of micro-debris, ultimately eliminating micro-voids or gaps between the metal substrate and the adhesive joint. Then, the standard K-300 adhesive (with hardener) is applied to the metal substrate surface. The adhesive bonding strength was determined using a single-lap shear test on varied surface conditions. The topography of surface-treated samples was analyzed using X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), and Contact Angle Goniometer. The grinding and acid-picking surface treatment increased the surface roughness of the substrate, which reduced the contact angle and improved the mechanical interlocking effect. The single lap shear test results show that the bonding strength of the grinded samples was superior to that of the acid-pickled samples. The RPC treatment further enhanced the bonding strength of all the grinded samples by 16.83–19.77 % and for acid-pickled samples by 20.79–44.97 %, which is higher than the values observed without RPC treatment. The combination of grinding and RPC surface-treated samples exhibited a superior bonding strength of 14.05 MPa. This value was 12.38 % greater than the bond strengths of acid-pickled samples, and the failure mode shifted from adhesive to cohesive failure mode. Thus, RPC treatment enhanced the wettability of metal substrates and maximized the utilization of contact areas on roughened substrate surfaces, consequently improving adhesive bond strength. These grinding and acid-pickling surface treatments are effective and well-suited for aerospace, automobile, and aviation applications.