Abstract
A principal investigation of the surface and shallow sub-surface region of corrosion protection coatings based on the ZnMgAl system was performed for three different compositions of Mg and Al, varying from 1.5 wt% up to 3.7 wt%, which are known to behave on a macroscopic scale in an interchangeable manner with respect to properties including corrosion resistance, forming behavior or weldability. Therefore, special attention was paid to the effect of the Mg and Al concentration on the chemical composition, structure and the thickness of the resulting native oxide surface layer as well as on the underlying microstructure of the coating on the nanometer scale. For this purpose the chemical composition of the naturally grown oxide surface layer was analyzed by means of X-ray photoelectron spectroscopy, whereas Auger electron spectroscopy was applied in order to obtain the spatial distribution of the surface constituents. Back-scattered electron micrographs revealed in addition the underlying coating microstructure. The thickness of the oxide surface layers was investigated by transmission electron microscopy. It was found that the resulting surface layers are rather similar, especially in terms of their chemical nature, and highly uniform, despite the high variations of Mg and Al concentrations of more than 100% for the different coatings. Only for the lowest here considered amounts of Mg and Al the thickness and composition of the oxide surface layer starts to reflect the underlying complex microstructure.
Published Version
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