Industrial components are used in a variety of applications, including the automotive industry, and they are manufactured from an ever-diverse range of materials. Among these, steel-based products remain significant due to the materials’ natural strength, workability, wide availability and low cost. Since many of these materials alone do not possess all the inherent properties needed to meet performance requirements, manufacturers use the enhancing benefits of surface coatings to bridge the gap between the base material properties and the end use requirements.

Many of these coatings have traditionally used the beneficial properties of materials containing hexavalent chromium. The automotive companies and their suppliers are facing a challenge to maintain or improve current performance while achieving the elimination of hexavalent chromium Cr (VI) materials from these surface coatings. This has become important because of the environmental need to reduce waste from end-of-life vehicles.

ELVD
The End of Life Vehicle Directive (ELVD) is the name given to the European Union directive 2000/53/EC [1] concerned with preventing waste generated by vehicles below 3.5 tons total permissible weight, through the reuse, recycling and recovery of end-of-life vehicles and their components.

The ELVD has been the subject of much discussion and numerous articles over the past couple of years, but essentially the directive sets out for member states to encourage vehicle manufacturers to limit the use of hazardous substances. After July 1, 2003, European Union member states are to ensure that materials used do not contain the heavy metals cadmium, lead, mercury and hexavalent chromium. Listed in the directive’s Annex II are exceptions for the above stated materials used in certain defined applications. In automotive related corrosion preventive coatings, Annex II listed that a maximum level of hexavalent chromium at 2 grams per vehicle would be allowed. This, therefore, will impact the hexavalent chromium materials found in surface coating layers (such as chromated passivation films on zinc electroplating and materials used in the formulation of zinc flake coatings). Not affected by the directive implications are hexavalent chromium materials used in chemical processing (which are regulated through other work place and environmental hazard related directives); therefore, chromium electroplate is not restricted by the ELV Directive.

The Directive affects the automotive supply chain, and applicators of surface coatings especially due to restrictions on the use of these materials. Among the most commonly specified automotive deposits has been the use of a traditional coating system using electroplated zinc followed by hexavalent chromium containing yellow chromate. Some uses for this deposit will require finishing with a post applied lubricant film (either an oil, wax or proprietary dry film lubricant) that would modify and control the torque and tension properties of the coating, allowing for predictable assembly performance.

The Directive means that this coating system will not be allowed in the future. The new ELVD compliant approach will be an enhanced multilayer system [2],[3],[4] , which for electroplated zinc will mean the use of either a zinc or zinc alloy deposit treated with a passivation film from trivalent or chromium-free chemistries. The layer can be subsequently finished with the application of a topcoat, such as a silicate based sealer type, an electrocoated paint film or a dip/spin applied zinc flake layer. A post-applied lubricant may also follow these. The use of a final topcoat film achieves increased corrosion performance of the layer, particularly with the need to meet modern testing procedures that specify pre-heating before corrosion testing [2]. The topcoat also enables the inclusion of an integral lubricant for controlled torque properties, enabling the elimination of an additional process step (Figure 1).

To comply with this EU Directive, the automotive supply chain has worked in varying degrees to generate data, issue pricing information and introduce alternative technologies. Perhaps the most activity has been from the German Automobile Association VDA (Verband Der Automobilindustrie), which established an internal working group in July 2000 to review alternative coating systems on a case-by-case basis.

The VDA “round robin” test for hexavalent chromium elimination was created, which studied 115 different electroplating system combinations and 8 different zinc flake coatings. Each combination had to be applied in production conditions (i.e., not in lab scale) with specific nominated applicators, and each coating was subjected to “standard tests.” This test phase was concluded in 2001, and a report presented at the Stuttgarter Automobiltag in December [5]. The conclusions for zinc flake coatings were generally positive, with the hexavalent-chromium-free systems achieving a higher overall rating than the existing Cr (VI) containing formulations.

Conclusions for the electroplated systems tested were not so clear and positive. It was noted that there was a large scattering in performance results for nominal comparable systems, and that no statement was possible on the long-term quality ability of the systems tested. Certainly it was commented that more close cooperation between chemical suppliers, applicators and the automotive industry would be necessary to obtain maximum performance from the electroplated hexavalent-chromium-free coatings. The complete implementation of the new coating systems across the industry would not be possible as a result of the ”round robin” test results; therefore, it was decided to establish a second test phase 2002 for electroplated coating types.

Claims have been made that there are around 6 m2 of surface area for zinc and zinc alloy coatings per vehicle, with an average of 1.4-1.5 m2 (13kgs) of coated fasteners. Opinions within the VDA are that the average hexavalent chromium content to be 4-8 grams per vehicle. Other studies within Europe and the U.S. have suggested a much lower level is present. Although data exists to assist the automotive engineer calculate the hexavalent chromium content in surface coatings (such as T. Biestek and J.Weber [6]), the general consensus seems to be that it is extremely difficult to accurately measure or predict its content in a vehicle; therefore, the logical approach would be to eliminate its use entirely.

In the face of such reasoning, speculation was rife that Annex II would be changed to reflect the current status of industry evaluation with the available technologies, and finally, after many months of uncertainty, the official announcement for the revision was made [7] on June 27, 2002. Adoption of these Annex II changes alters the date of compliance and concentrations permissible for hexavalent chromium use in corrosion preventive coatings. From July 1, 2007 hexavalent chromium in corrosion preventive coatings is limited to 0.1% (w/w) per homogeneous material, provided that it is not intentionally introduced. The term “intentionally introduced” is a new phrase that means “deliberately utilized in the formulation of a material or component where its continued presence is desired in the final product to provide a specific characteristic, appearance or quality.” In the case of hexavalent chromium in chromate passivation films, this would seem to address the phenomenon where a small amount of hexavalent chromium may be detected in coating layers produced from Cr (VI) free chemistry with certain formulations under certain conditions [2].

This new milestone better reflects the original recommendations from the final report prepared by the Commission consultant Ökopol [8] on Heavy Metals in Vehicles II issued July 2001. The report was compiled following extensive consultation and discussion with many leading companies and associations within the automotive supply chain. In the report summary, the complexity of use and function of hexavalent chromium in vehicles were noted. Among others, the following recommendations were made:

• Phase out of transparent and blue chromated systems by July 7, 2002.
• Phase out of Cr (VI) in zinc lamella systems, electrophoretic paints and in fixation ground for additional layers of paint by January 1, 2005 with a review date in 2003.
• Phase out of Cr (VI) in black and olive-chromated surfaces by January 1, 2007 with a review date in 2003.

The realistic conclusion was that a total phase out of hexavalent chromium is possible by 2007, and the threshold value of 2 grams Cr (VI) per vehicle should be deleted because a standardized analytical procedure for Cr (VI) is difficult to establish.

Since the Ökopol report was completed, a qualitative procedure has now been issued through the German suppliers association ZVO [2],[9] (Zentralverband Oberlächentechik), which enables a qualitative analysis for the content of hexavalent chromium in colorless and colored chromate coatings with and without sealers. The method uses the oxidizing ability of Cr (VI) against Diphenylcarbazide to produce a color change. This change can then be referenced on a color match chart to provide a visual evaluation assessment (Figure 2).

Additional testing methods include the use of a boiling-out procedure in deionized water followed by UV/VIS spectrometry measurement, as detailed in the ZVO procedure ZVO-010-UV-05e, to produce a quantitative result.

IMDS
The International Material Data System (IMDS) [10] is an electronic system devised to assist the automotive industry with compliance reporting concerning legislation and EU directives such as the ELVD. Although not directly related, the ELVD approach provided motivation to the German automotive industry for such a system, since it highlighted the need to clarify the composition of supplied parts, including their surface coatings.

The IMDS is a joint project started by several major European car manufacturers (such as VW, BMW, DaimlerChrysler and Volvo) in partnership with ElectronicDataSystems. Support and co-operation has since expanded to the North American automotive operators such as GM and Ford, while Italian company Fiat and Japanese manufacturer Toyota have recently joined the scheme. It replaces the Material Data Sheet for first batch reporting, and it allows the manufacturer to review and collect data for compliance reporting to corporate and governmental standards and regulations.

This new electronic system assists the car manufacturers by allowing fast access of data on critical substances, enabling judgment on the material composition of vehicles and components during their R&D and product development phases, which may be rated as critical in the future, and providing material composition data for parts delivered to other OEM’s.

Companies who supply components and assemblies to the automotive industry are all affected by this new electronic reporting system, and are responsible for submitting information relevant to their individual product supplies. Support for details related to surface coatings will be from the applicators that become jointly responsible for entering information related to their surface coating layers.

The IMDS has an Internet site located at www.mdsystem.com, which provides an excellent source of background information about the system. The FAQ (Frequently Asked Questions) section of the public access pages details recommendations regarding the reporting of hexavalent chromium contents of chromated zinc and zinc alloy coatings (Figure 3). Remarks on these values confirm that an analytical procedure has yet to be confirmed by the EU. For clear/transparent passivations produced from hexavalent-chromium-free solutions, these can be assumed as having a Cr (VI) content of 0 µg/cm2.

From July 10, 2002 it has become possible for manufacturers and applicators to register for access through completion of an on-line registration form on this web site. Login for entering information is achieved by entering a user designated ID and password, which will be issued after the registration application has been processed.

Through the IMDS, a list of data is available for basic substances, the VDA list of notifiable materials (VDA 232-101) and a list of construction materials (such as steel-iron and aluminum). To assist the fastener manufacturer, various tools can be found on the site such as the calculation program for the surface area of fasteners, provided by the German fastener association Deutscher Schraubenverband E.V. (DSV). An applicator of surface coatings can search the IMDS database for composition information relating to their coating layers through the use of ID numbers and Logical names for each “data-set” (Figure 4). A database containing compositional information for different types of electroplated coatings has been generated through the German trade association Zentralverband Oberflächentechnik, following collaboration between the major chemical supply companies. The database is not commercial; therefore, supplier names and proprietary product details are not listed. Within the database, chromate passivation films containing hexavalent chromium are referenced as chromate films, whereas films free of hexavalent chromium are identified as passivates.

In this way, it becomes possible for the component manufacturers with support from their surface coatings applicators, to provide the necessary compositional information relevant to their individual supplies. It is therefore possible to complete the appropriate IMDS information fields without having to have specific technical knowledge about the substrate and coating layer.

The implementation date of the EU’s ELVD for defined heavy metals is July 1, 2003. The newly revised Annex II offers a date extension and new conditions for the use of hexavalent chromium in corrosion coatings. The new conditions will certainly have the effect of slowing the change away from alternative processes, but this will only be a short-term delay. Conversion to hexavalent-chromium-free (Annex II compliant) technologies is certain to be introduced for some new automotive parts where cost and performance are not compromised. Considering the health and environmental pressures, the future for surface coating of components is certain to be hexavalent chromium free.

The introduction of the automotive IMDS points the way to a future of increased regulation for materials used by manufacturers, and the need to have a better level of cooperation between all companies involved in the supply chain. A greater understanding means industry will be better equipped to handle changing social, economic and environmental issues in the future.