Improvement of Polymer/Metal Adhesion Using Anodizing Treatment and 3D Printing Process

Joining materials with different physicochemical properties presents significant challenges. This study investigates the one-step anodization of aluminum in a mixed phosphoric acid and hydrogen peroxide solution, followed by the direct injection molding of polymer resin to enhance joint properties. The anodizing treatment is performed at constant electrical current with phosphoric acid solutions of various concentrations. Phosphoric acid anodizing enables the formation of 3D channeling pore structure with micropits and uniform nanopores on the aluminum surface. Hydrogen peroxide acts as an oxidizing agent and promotes the dissolution reaction, thereby increasing the size of the nanopores. Larger pores facilitated the penetration of polymer resin into the aluminum oxide layer during injection molding, resulting in bonding strengths up to 40.34 MPa. This improvement is substantial when compared to the bonding strengths achieved through conventional injection molding processes. These results highlight that the increase in nanopore size due to hydrogen peroxide addition played a critical role in enhancing the bonding strength, as it facilitated better penetration and interlocking of the polymer resin within the anodized aluminum layer. Furthermore, a three-dimensional (3D) printing process was able to join polymer resins to the anodized aluminum surface, where the larger nanopores with the addition of the hydrogen peroxide is more beneficial to the bonding strengths than the direct injection molding is. This alternative approach addresses the environmental issues associated with the use of Cr(VI)-based anodizing solutions and the lightweight composites with applicability to various industries that could be produced using this method.