Corrosion Protection for Magnesium Based Alloys

One of the main reasons preventing larger scale use of light magnesium alloys is their high corrosion susceptibility. Improving the corrosion protection of Mg alloys without loosening high strength/weight ratio is a real challenge that could lead to a breakthrough in many areas, especially aeronautics and automotive.
We report on a complex anticorrosion multilayer coating system for the light magnesium alloys AZ31 and ZK30. Environmentally friendly corrosion inhibitors for magnesium alloys were combined with a thin hybrid sol-gel coating without the deterioration of the barrier properties of the coating and deactivation of the inhibitors. For this purpose, the intermediate porous layer of magnesium oxide obtained by anodization process served as a reservoir of corrosion inhibitors, placed under the sol-gel coating.
Such protective system profitably combines the increase of corrosion resistance of the magnesium substrate due to an additional oxide layer, the improvement of adhesion of the thin sol-gel coating to the porous anodized surface along with gaining of active protection properties conferred by the corrosion inhibitors safely impregnated into the porous reservoir.
The effect of corrosion enhancement from the anodised layer due to increase of relative content of aluminium on the surface of the anodized magnesium-based alloys will also be discussed.