The influence of microstructure on the corrosion behaviour of AZ91DbyScanning Kelvin Probe Force Microscopy and Scanning Kelvin Probe

摘要

Scanning Kelvin Probe (SKP), Scanning Kelvin Probe Force Microscopy (SKPFM)rnand Scanning Electron Microscopy (SEM) investigations have been used to investigaternthe influence of microstructure on the corrosion of magnesium alloy AZ91D.rnIntermetallic compounds present in AZ91D have been synthesized in order to preparernbulk electrodes. These electrodes have been then examined using Scanning KelvinrnProbe (SKP) and electrochemical techniques. The results obtained have been comparedrnwith measurements made on an AZ91D alloy at the nano scale, using Atomic ForcernMicroscopy (AFM), Scanning Electron Microscopy (SEM) and Scanning Kelvin ProbernForce Microscopy (SKPFM) techniques. The results show that the Volta potentialrnmeasurements made with Scanning Kelvin Probe (SKP) on synthesized intermetallics,rn(e.g. bulk electrodes) give similar results when compared to the Volta potentialrnmeasurements made on AZ91D using SKPFM at the submicron scale.rnFrom the results it is also obvious that the intermetallics particles show a clear Voltarnpotential contrast with respect to the matrix, which allows a detail mapping of the Voltarnpotential. The noble Volta potentials measured for β-Mg17Al12 and η-Al8Mn5 are in goodrnagreement with the corrosion potential values measured in solution. The difference inrnVolta potential measured between the intermetallic particles and the matrix as well asrnthe gradient in Volta potential measured in some intermetallic particles may explain thernlocalised corrosion attacks observed on AZ91D in chloride environments. Hence fromrnthe results, it is shown that SKPFM is a valuable tool to measure lateralrninhomogeneities on surfaces at submicron scale.