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Abstract
Inorganic nanoparticle based coatings for magnesium alloys were developed and tested for their performance in corrosion protection. Nanoparticles are characterised by a high sintering activity. This allows to obtain inorganic coatings by a sintering process at rather low temperatures which is suitable for magnesium alloys. Coating sols are based on silicon dioxide and sintering additives such as boron or sodium oxide. One technique is based on aqueous, commercial nanosols which can be applied by dip or brush coating to form layers on AZ31 and AZ91. Another technique is based on the electrophoretic deposition of silicon dioxide nanoparticles which also contain boron and phosphorus oxide. Crack free layers with a thickness of up to several micrometres could be obtained by a two step process including a bimodal particle distribution and polydiethoxysiloxane as adhesion promoter. The composition and surface structure of these novel coatings are characterised by modern analytical methods including SEM and atomic force microscopy and their applicability as protective coatings is investigated by using electrochemical impedance spectroscopy.