The effect of surface treatment methods on the bonding strength of aluminum and polypropylene plates bonded with epoxy adhesive

With advancing technology, the diversity of materials used in manufacturing sectors has significantly increased. In this context, composite materials have become widely used in many aspects of our lives. Aluminum-Polypropylene (Al-PP) composite materials combine lightweight and high durability characteristics, making them one of the most commonly used materials in aircraft structures. Additionally, they find extensive applications in industries such as automotive, electronics, construction, and packaging. In this study, surface treatments such as sanding, sandblasting, chemical etching, anodization, and microwave vacuum plasma were applied to PP and Al plates in various combinations, followed by bonding with epoxy adhesives. Experiments were conducted to investigate the synergistic effects of these parameters on the adhesion strength between PP and Al plates. Furthermore, to explore the impact of different adhesives and aging processes on adhesion strength, surface-treated plates were bonded with epoxy adhesives prepared using Teta, Mx, and B3 curing agents. After curing, the samples were immersed in water at 50°C for varying durations to evaluate the influence of different environmental conditions on adhesion strength. The highest strength was achieved by applying sanding and cold plasma to PP plates, and chemical etching, anodization (20 min), and cold plasma to Al plates. This combination resulted in a 558.72 % improvement in adhesion strength compared to untreated plates (1840 N, 9.2 MPa). For sandblasted aluminum plates, the highest adhesion improvement was achieved with a 25-minute anodization process, while plasma treatment shortened the required anodization time, yielding optimal results with a 15-minute process. Aging processes applied to the plates joined with various surface treatments and curing agents were found to negatively affect adhesion strength. This effect varied depending on the type of adhesive used and the surface treatment applied. In the final stage of the study, surface treatments providing maximum adhesion strength were applied to the plates, followed by hot water aging, and the effect of this process on adhesion strength was examined. The results revealed that while chemical etching, anodization, and plasma surface treatments on Al plates initially provided relatively high adhesion strength, the combination of sandblasting, anodization, and plasma treatments exhibited better performance in terms of strength retention after aging. Additionally, it was determined that plasma-treated surfaces showed lower strength loss after aging.