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.
