Life extension of trivalent chromium passivation baths and enhanced product performance

Abstract

Although Cr (III) based passivation processes are mature, there is always pressure from end users to improve the performance of passivation films. The effect of incorporating ceramic nanoparticles into the film on the corrosion protection of steel components is reported for zinc coatings, with particular emphasis on cobalt-free processes. A novel technology based on selective ion-exchange to remove contaminants such as iron and copper as well as dissolved zinc from trivalent chromium baths is also described. Removal of these metals simultaneously without any appreciable reduction in chromium concentration rejuvenates the system and increases bath life significantly. This reduces not only the cost of frequent make-ups but also the load on the effluent treatment system, and imparts greater consistency to the life and appearance of the components processed. The concept can be extended to baths for chromating of aluminium and its alloys. Technical data generated from actual industrial installations are presented and discussed.

This paper is based on a presentation given at the IMF TransFair 2013 conference held at The Heritage Motor Centre, Gaydon, Warwickshire, UK, on 11–13 June 2013.