In-situ study of the formation process of stannate conversion coatings on AZ91D magnesium alloy using electrochemical noise

The formation process of stannate conversion coating (CC) on AZ91D alloy was in-situ investigated by electrochemical noise (EN). The wavelet transform, as well as noise resistance (Rn) and spectral noise resistance (Rsn), had been employed to analyze the EN data. It was revealed that there exist two distinguishing stages of stannate CC formation process on AZ91D alloy, including an incubation stage companying with the nucleation and nuclei dissolution process, a periodical growth stage involving hemispherical particles growth and coating dissolution process. Furthermore, the results demonstrated that EN was a powerful tool to investigate rapid electrochemical process, such as CC formation process.