Interfacial bonding and corrosion behaviors of HVOF-sprayed Fe-based amorphous coating on 8090 Al-Li alloy

To solve corrosion problems of Al-Li alloys in marine environment, Fe-based amorphous coating was first deposited on 8090 Al-Li alloy by high velocity oxy-fuel spraying. The microstructure, interfacial bonding and corrosion behaviors of the Fe-based amorphous coating are investigated. It is found that the coating is mainly composed of amorphous splats, but a few crystalline phases can be observed in the splats or splat surfaces. Even so, the corrosion resistance of the coated 8090 alloy is 7 times higher than that of the bare 8090 alloy. Moreover, due to the partially melting and rapid cooling of substrate during metal droplet deposition, there is an amorphous transition zone at the AMC/8090 alloy interface, indicating the formation of localized metallurgical bonding. Owing to the metallurgical bonding interface and the high compactness of coating, the adhesion strength of Fe based amorphous coating can reach 58.2 MPa. In 3.5 wt% NaCl solution, a bipolar passive film can be formed on the Fe-based amorphous coating, and its compactness decreases as the polarization potential increases. Because of the aggregation of Cr element and the uneven passive film, the crystallized splats and crystallized splat surfaces are eroded preferentially, leading to the formation of corrosion channels and the corrosion failure of coating. The present work provides a guidance for the design of corrosion-resistance coatings on Al-Li alloys.