Corrosion resistance and electrical contact resistance of a thin permanganate conversion coating on dual-phase LZ91 Mg-Li alloy

A strongly acidic permanganate conversion coating solution containing 0.1 M KMnO4 at pH 1.5 adjusted with H2SO4 was employed for LZ91 magnesium-lithium alloy, realizing the formation of a thin protective coating with a low electrical contact resistance. The corrosion resistance of LZ91 alloy was markedly improved by the permanganate conversion coating, which consisted of MgO, MnO2, and Mg(OH)(2). Coating formation proceeded on both the alpha-Mg phase and beta-Li phase in this strongly acidic permanganate solution, achieving a full coverage of permanganate conversion coating within a short treatment time. When the immersion was prolonged to 30 s, cracks were present on the permanganate conversion coating, which deteriorated the corrosion resistance substantially. Moreover, the increase in the thickness of the coating elevated the electrical contact resistance. However, the relatively thin areas on the thin permanganate conversion coating became active sites where corrosion commenced. As a result, a thin uniform permanganate conversion coating is crucial for both enhanced corrosion resistance and reduced electrical contact resistance. (c) 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

The use of a strongly acidic permanganate conversion coating can significantly improve the corrosion resistance of magnesium-lithium alloy, while forming a thin and uniform coating is crucial for reducing electrical contact resistance.