|Period:||01.08.2012 - 31.01.2014|
|Project Manager:||M.Sc. Dominik Tabatabai|
Scope of work
The combination of low density with good mechanical properties makes magnesium alloys superior to many other metals, plastics or composites in modern lightweight construction. The weight saving extends not only the construction possibilities, but also the energy efficiency of cars, planes or helicopters.
However, the susceptibility to corrosion of magnesium alloys causes some problems and good corrosion protection is essential for most applications. Established protective coatings, especially chromate containing coatings, cannot be used anymore due to environmental regulations. Alternative methods like plasma anodizing, affect the energy balance negatively.
Aim of the project
Protective coatings which combine corrosion protection with environmental sustainability should be developed for established magnesium alloys (i.e. AZ31 and AZ91). Additional organic or inorganic finishing and painting should still be possible.
In this project, the focus is the combination of chemical conversion with nanoparticle based coatings. Two approaches should be investigated:
A) a single-stage process, especially for single-phase alloys with low aluminium content. Here during the conversion in nanoparticle dispersions the nanoparticles should become incorporated into the growing conversion layer.
B) a two-stage process, which should also be suitable for multi-phase magnesium alloys. Here a porous nanoparticle based primer should be applied first, which should facilitate a consecutive homogeneous chemical conversion.
Both processes should be accomplished at higher pH values than conventional conversion to increase the protection of the Mg2+-based coating. The nanoparticles should help to increase the coating density as well as the coating thickness. Especially process B) should enable to neglect the influence of phase-dependent surface potentials, typical for aluminium-rich magnesium alloys, and to form homogeneous conversion coatings.
Here the main-focus is the increase of the barrier properties of the coating, by an increase of the coating thickness, less cracks and a higher abrasion resistance. However, the self-healing abilities of chromate conversion coatings should be accomplished at best by the addition of environmental friendly corrosion inhibitors, e.g. rare earth salts.
Das IGF-Vorhaben Nr. 17250 N der Forschungsvereinigung DECHEMA e.V., Theodor-Heuss-Allee 25, 60486 Frankfurt am Main wurde über die AiF im Rahmen des Programms zur Förderung der industriellen Gemeinschaftsforschung (IGF) vom Bundesministerium für Wirtschaft und Energie aufgrund eines Beschlusses des Deutschen Bundestages gefördert.