Post-anodization methods for improved anticorrosion properties: a review

Abstract

Anodization is a prominent surface treatment for light alloys that has been successfully used in the industry for the last two decades as it provides effective corrosion and wear protection. However, anodic films have porous structures, and the period of corrosion protection is limited by the nature of anodic pores, through which corrosive species may enter and reach the substrate surface. To seal the anodic porous layer, various post-anodization treatments have been developed. The most commonly employed post-treatments are the layered double hydroxide (LDH), sol–gel, hydrothermal, and cerium-based methods. Recent research revealed that after applying these post-treatments to various anodized magnesium alloys, the corrosion resistance of the resulting coatings is sufficiently enhanced because the post-layers seal the pores in the anodic thin films. This article reviews the recent research progress regarding post-anodization coatings formed on anodized magnesium alloys. Furthermore, the corrosion protection performance and microstructural changes of the resulting coatings are elucidated. The LDH method was found to be the most beneficial sealing treatment, as the treated anodized specimens demonstrated excellent corrosion resistance and a significant self-healing effect. In contrast, less satisfactory protection properties were obtained using the sol–gel, hydrothermal, and cerium-based sealing methods.