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The European End-of-Life Scrap Vehicle Directive approved in September of 2000 effectively bans the use of hexavalent chromium in automotive applications after July 1, 2003. In response to the directive, The United States Council for Automotive Research (USCAR) will disallow the use of hexavalent chromium in corrosion-resistant coatings effective July 1, 2002. A new, chromium-free coating became commercially available in 1998 which provides a solution to this new directive. The coating is zinc- and aluminum rich, silver in color, thin, water-based, volatile organic compound (VOC) compliant, and contains no toxic metals. It is heat resistant and offers excellent corrosion protection without adversely affecting brake performance. This report summarizes validation testing for the automotive industry of brake rotors coated with the new, chromium-free coating.

Proving Ground cyclic testing was used to evaluate vehicles assembled with electrogalvanized and organic composite coated electrogalvanized steel. These same materials, along with several commonly available precoated steels, were also evaluated as hem flange assemblies on towed trailers at the Proving Ground. Testing was terminated as perforation of some of the assemblies occurred. Pitting depth was used to quantitatively evaluate metal loss.

There is currently no widely accepted accelerated test used by the automotive industry to evaluate perforation (inside-out) corrosion. Historically, automotive companies have used Proving Ground evaluations of full vehicles to assess perforation corrosion. Such tests are expensive, do not lend themselves to comparative testing of a large matrix of materials or processes, and are not available to supplier companies. The Perforation Subcommittee of SAE ACAP Division 3 has initiated a project to obtain perforation corrosion data from on-vehicle exposures that will lead to the development of appropriate laboratory perforation corrosion tests. The first phase is the development of a test specimen and methods to evaluate corrosion on this specimen. The proposed specimen is a two-panel assembly having an un-painted test area separated by a gap distance of .25 mm.

The development of a new corrosion-resistant coating composite for automotive sheet metal is described. The three-layer coating combines the galvanic properties of a thin electroplating with the passivating and barrier protection of an inorganic intermediate layer and an organic outer layer. The combined effect of the composite is to act as three lines of defense against corrosion. The organic top layer provides barrier protection, while the inorganic intermediate layer provides passivation to slow down corrosive reactions once the barrier is breached. The plating layer provides galvanic action as the last line of defense, being called into play only after the initial two coatings are exhausted. The zinc coating then corrodes galvanically to protect the underlying steel. Corrosion tests indicate that this combined coating is more effective than the individual coatings alone.

This paper describes the work done to develop an environmentally friendly coating which provides corrosion protection to fasteners and stamped parts. It is a water based, neutral pH, VOC compliant coating that contains zinc and aluminum metal flakes in an inorganic binder system. It is free of all highly regulated heavy metals and carcinogens. The coating can be applied by either dip-spin, dip-drain or spray coating processes, resulting in a dry film thickness of 0.3-0.4 mils (7.5-10 microns) which is silver in color. Curing of the coating utilizes conventional industrial ovens and has a wide cure window. The structure of the coating, mechanisms of corrosion protection, and test results will be presented.