Nanochemical impregnation of Modified Phosphoric Acid Anodised (MPAA) layers - a promising replacement for Chromic Acid Anodising (CAA)

S.K. Weidmann, K. Kremmer, M. Schneider, W. Fürbeth

Proceedings EUROCORR 2011


A high corrosion resistance in combination with good adhesion properties is often
required for the application of aluminium alloys. Nowadays these demands are
mainly fulfilled by chromicacid anodising which has to bereplaced by less hazardous
processes. Therefore the aimof the presented work is the development of a surface
treatment which providesas good corrosion and adhesion properties as chromic acid
anodising. For this purpose open porousoxide layers have been prepared by a Modified Phosphoric Acid Anodising Process (MPAA-process) and impregnated via
chemical nanotechnology. The aim wasto find an impregnation method to enhance the thickness of the barrier layer andconsequently the corrosion resistance. However, the pores shall not be sealed completely in order to preserve the good adhesion properties by the residual porosity. A promising impregnation has been obtained by a dip coating process with commercially available silica nanoparticle dispersions. The impregnation parameters have been investigated systematically and a model of the impregnation mechanism is being developed. The adhesion properties have been investigated and are very promising. First corrosion tests showed promising results but further tests are necessary and are being carried out.

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