Magnesium is the lightest of all construction metals. Therefore there is a high interest in the use of its alloys in areas where weight reduction is of high importance. Magnesium alloy AZ91, for example, is approximately 25% lighter than aluminium. Today magnesium alloys are applied in the automotive area, where weight reduction of specific components like steering wheels or seat frames allows the reduction of energy costs. Further fields of application are hand tools or mobile electronic devices like mobile phones. However, a broader use of magnesium alloys is limited by their high susceptibility to corrosion.
A good level of corrosion protection can be obtained by coatings which contain Cr(VI) compounds. These compounds offer sustained corrosion protection due to their self-healing properties, but at the same time they are highly carcinogenic. Therefore, the search for less critical corrosion protective systems which offer a comparable level of protection is of high priority.
By applying an anodic oxide layer to magnesium alloys they are provided with some basic level of corrosion protection. The incorporation of encapsulated corrosion inhibitors into the oxide layer enhances the level of protection and adds self-healing abilities to the system, which provides protection even if the applied oxide layer is damaged.
As corrosion inhibitors rare earth compounds are used, which are a non-hazardous alternative to Cr(VI) compounds. The embedment of the inhibitors into nano particles (encapsulation) allows their specific and triggered release.
Since relatively low voltages are applied, the anodizing process should require less energy than conventional anodizing processes. By replacing Cr(VI) with non-hazardous corrosion inhibitors, environmental regulations are accomodated. The goal is a sustainable corrosion protection system for magnesium alloys, which provides enduring protection while requiring a relatively low energy input and no ecologically problematic substances.
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