Influence of Plasma Electrolytic Oxidation Coating on the Interface of an Aluminum Alloy/Glass Fiber Reinforced Thermoplastic Composite Obtained by Ultrasonic Welding

Abstract

This study investigated the influence of an oxide coating generated by Plasma Electrolytic Oxidation (PEO) on the adhesion between AA2024 aluminum alloy and a glass fiber-reinforced polyetherimide (PEI) composite using ultrasonic welding. After welding, the joints were subjected to lap shear testing (ASTM D1002:19) to evaluate mechanical strength, and the fracture surfaces were analyzed for failure mode (ASTM D5573:19) and by scanning electron microscopy (SEM). Samples without PEO treatment exhibited an average shear strength of 5.4 MPa, with failure predominantly by adhesive fracture (ADH), where little to no thermoplastic matrix remained adhered to the aluminum. In some regions, thin-layer cohesive fracture (TLC) was observed, indicating interface failure with a thin residual polymer layer. On the other hand, PEO-treated samples showed a shear strength of 4.2 MPa and failure characterized by fiber rupture and interlaminar fracture of the composite, with fibers strongly bonded to the polymer matrix after testing. This suggests that the PEO treatment promoted a more robust interfacial adhesion, shifting the failure point to the interior of the composite. Although the shear strength was slightly lower in the treated samples, the change in failure mode indicates improved interface integrity, highlighting the potential of PEO for applications requiring efficient joining of dissimilar materials.