In this study, the ductile iron was treated with austempering heat treatment to become as austempered ductile iron (ADI) substrate. The surface treatment was to first use electroplating copper as the intermediary layer (25 μm), and then apply the cathodic arc deposition to coat the TiAlN film (3 μm). Then the post heat treatment and various corrosion tests (polarization test, immersion test, and salt spray test) were conducted to explore the effect of post heat treatment on the corrosion resistance of composite surface coated ADI.The experimental results showed that the ADI after composite coating (copper electroplating and arc coating TiAlN) and post heat treatment could not degrade the excellent microstructure of the substrate. The composite coatings had good adhesion, and post heat treatment could not affect the adhesion of the coatings. In terms of surface hardness, composite coating could significantly increase the hardness of ADI. In terms of corrosion, after polarization test, salt spray test and immersion test, it is found that the TiAlN film with the Cu interlayer is more resistant to corrosion than that without the interlayer. It is inferred that the interlayer has a mitigating corrosion agent that directly enters the substrate to achieve protection. After the post heat treatment, the corrosion resistance of the coatings is slightly reduced due to the precipitation of CuO.
Keywords: Austempered ductile iron, TiAlN film, Electroplating copper, Post heat treatment,