Enhanced bonding of polyphenylene sulfide-aluminum alloy composites using combined mild and hard anodizing techniques

High-strength direct joining between polymers and Al has attracted considerable attention, particularly for reducing the weight device. In this study, porous anodic alumina (PAA) films were fabricated on a commercial 6063 Al alloy using with mild and hard anodizing with varying durations, followed by etching. Subsequently, polyphenylene sulfide (PPS) was directly joined with Al through injection molding. The correlations between the interface bond strength of PPS-Al joints and the Al oxidation duration were systematically investigated. The porosity, diameter of nanopore, and wettability of anodic aluminum oxide (AAO) film surface significantly influenced the bonding strength of PPS-Al composite structure. The porosity increased with an etching duration, increasing the bonding strength. However, excessive porosity (>54 %) weaken the films and reduced their bonding strengths. When the durations of mild anodizing (MA), hard anodizing (HA), and etching treatment were set to 30, 30, and 60 min, respectively, the maximum bonding strength reached 25.2 MPa, approximately 77 % of the base-material shear strength. Scanning electron microscopy revealed nanopillars with two different top sizes (approximately 80 and 110–130 nm) on the surface of injection-molded PPS, which were attributed to the different anodizing preparation voltage. These findings are generally significant for the realization for high-strength direct-bonded polymer-Al joints.