Influence of microstructure on the atmospheric corrosion behaviour

2 SEM back-scattered image of AZ91D Mg alloy showing a-phase grains. In the grain boundaries the p-Mgi7Ali2 phase can be found (1). Between the a-phase and the a-phase a eutectic area of p-phase and a-phase precipitates. AlsMns inclusions are also present in the alloy (2). 

1 Characterisation of potential distribution and corrosion attack morphology in atmosphere conditions 

The corrosion processes of Mg alloys in the atmosphere as well as in solutions lead to corrosion attacks which are inhomogeneously distributed over the surface with a localised and preferential attack of some alloy constituents. The difference in the electrochemical properties of different phases and intermetallic particles in the alloys is of great importance for the corrosion mechanisms. It is therefore important to be able to measure the potential differences between the phases. Dnring recent decades there has been a rapid 

5 Left SKPFM image of AZ91D alloy. Right field emission gun scanning electron microscopy (FEG-SEM) image of the same area. The compositions and Volta potentials of points 1-4 are given in Table 7.5. 

Location Concentration (atom %) Phase Volta potential (mV vs. SHE) 

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