General presentation
Hexavalent chromium-free conversion treatments

Under the impetus of the automotive industry, as part of the recycling of end-of-life vehicles, a project was launched to totally eliminate hexavalent chromium from zinc conversion coatings. This project took the form of a European directive [1] requiring, first and foremost, that the maximum admissible quantity of hexavalent chromium be reduced to 2 g per vehicle by July 1 2003. At the same time, automakers' requirements in terms of the anti-corrosion performance of protective coatings remained unchanged, or even increased in some cases, particularly with regard to resistance to thermal testing. The nature of the tests has also evolved, with automakers moving towards in-vehicle or cyclic testing to complement the salt spray test.

The scale of the task and the associated...