Self-healing characteristics of praseodymium conversion coating on Magnesium studied using Scanning Electrochemical Microscopy

Application of rare earth conversion coatings as a surface treatment for magnesium has been subject of several studies revealing its potential as an effective passivating layer. This paper presents a study on a rare earth conversion layer based on Pr(NO3)3 as surface treatment for AZ80X magnesium alloy in simulated biological (buffered) solution. Scanning electrochemical microscope (SECM) was used to investigate protective properties and degradation behaviour of Pr conversion layer with a local approach. Self-healing properties of the conversion layer in presence of Pr3+ was also studied using SECM. Results revealed the self-healing characteristic of Pr conversion film in presence of active, Pr3+, species. Pr conversion layer improved corrosion resistance in the short term by producing an electrochemically inert and insulating layer. SECM results in potentiometric mode elucidated the role of near surface pH in the formation of conversion coating.