Effect of Sintering Time on the Corrosion Resistance of PTFE Coatings on AZ31 Mg Alloy

Abstract

Corrosion is one of the key technical problems impeding the widespread use of magnesium (Mg) and its alloys. Consequently, enhancing the corrosion resistance of Mg alloys is an urgent issue that necessitates immediate attention in their applications. Polytetrafluoroethylene (PTFE), often termed the ‘king of plastics’ because of its exceptional chemical inertness and non-reactivity, forms coatings that effectively shield metal substrates from corrosive environments. This capability substantially reduces corrosion rates, underscoring its considerable potential in corrosion prevention. In this study, PTFE coatings were successfully prepared on Mg–3Al–1Zn (AZ31) alloy sheets through electrophoretic deposition (EPD). The coatings underwent sintering treatments of varying durations, and their corrosion resistance properties were systematically evaluated. The results indicate that sintering duration critically influences the microstructural morphology of the PTFE coatings; extending the sintering duration within a specific range enhances the microstructure’s compactness. Furthermore, the study examined the corrosion behavior of Mg alloys coated with sintered PTFE in a 3.5 wt % NaCl solution, where the corrosion resistance of the sintered PTFE-coated AZ31 was significantly enhanced. Notably, coatings sintered for 14 h exhibited the highest corrosion resistance, with the corrosion current density decreasing from 4.05 × 10^–5 A cm^–2 for the bare AZ31 to 1.20 × 10^–7 A cm^–2 for the sintered PTFE-coated AZ31. Concurrently, the charge transfer resistance increased significantly from 227 to 2.72 × 10⁵ Ω cm². The coatings achieved a contact angle exceeding 123° and an adhesion rating of 5B. This offers a novel approach for mitigating corrosion in Mg and its alloys.