Investigation of AZ91D Magnesium Alloy Corrosion Behavior under Thin Electrolyte Layer Using Nondestructive Electrochemical Techniques

Abstract

In order to investigate the corrosion behavior of AZ91D magnesium alloy under thin electrolyte layers (TELs) in 3.5 wt. % NaCl solution during short immersion time, some nondestructive electrochemical measurements such as the electrochemical impedance spectroscopy (EIS), electrochemical noise (EN) and cathodic polarization curves were conducted. In addition, scanning electron microscopy (SEM) attached with energy dispersive X-Ray spectroscopy (EDS) and Scanning Kelvin Probe Force Microscopy (SKPFM) were employed to character the microstructure and the Volta potential distribution of AZ91D magnesium alloy surface. The experimental results reveal that the corrosion rate of AZ91D under TELs is slower than that in bulk solution and decreases with the TEL thickness thinning. Both the anodic and cathodic reactions were restrained under TELs, especially in thickness thinning to around 200 μm and lower. Furthermore, pitting corrosion is initiated at the matrix adjacent to the noble β phase particles and crevice corrosion is dominant at the early corrosion stage under TEL.