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     Chemical Conversion films on aluminum are applied by either the immersion in or spraying on a chemical mixture composed primarily of hexavalent chrome.  The National Institute for Occupational Health and Safety (NIOSH) considers hexavalent chrome as a potential occupational carcinogen.

 

     For several years, the Occupational Safety and Health Administration (OSHA) has looked at hexavalent chrome and is now in the process of revising the rule on exposure to hex-chrome.  The revision process went through industry and public input as well as public hearings.

 

IMPORTANT NOTICE

 

The OSHA Final Rule on Hexavalent Chrome was issued on February 28th, 2006!

 

IMPORTANT NOTICE

 

     Other than OSHA or EPA Rules regarding use, there are no US laws regarding the restriction of use of these substances.  However, several states have enacted laws regarding the disposition of electronic waste.  Additionally, there is now a bill (HR 425) before Congress regarding electronic waste.

 

     In the global scope, the European Union issued Directive 2002/95/EC (RoHS) on the restriction of the use of certain hazardous substances in electrical and electronic equipment.  Essentially this Directive mandates from 1 July 2006, new electrical and electronic equipment put on the market does not contain lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls (PBB) or polybrominated diphenyl ethers (PBDE).  Two other EU Directives worth mentioning are Directive 2000/53/EC (ELV) on end of life vehicles and Directive 2002/96/EC (WEEE) on waste electrical and electronic equipment.

 

     A great deal of work has been done by the Joint Group on Pollution Prevention (JG-PP) regarding a suitable replacement for hexavalent chrome coatings.  The result of this work is the identification of some alternatives to hexavalent chrome (see Non-Chromate Aluminum Pretreatment Phase I and Phase II Reports).

 

     Chemical Conversion films on aluminum are specified in accordance with one of several standards.  Globally, the ISO 8081 standard is used.  In the United States, either Mil-C-5541, AMS 2473 or AMS 2474 are the basis for specification.  ISO 8081 has long accounted for non-hexavalent chrome processes.  In the United States, only recently have standards begun to reflect non-hexavalent chrome options.  In 2002, ASTM issued ASTM B 921 - Standard Specification for Non-hexavalent Chromium Conversion Coatings on Aluminum and Aluminum Alloys.  Within the military specification system, chemical conversion films on aluminum are actually governed by three documents.  One document (Mil-DTL-81706) governs the material specifications for the chemical used to produce chemical conversion films.  The second document (Mil-QPL-81706) governs materials qualified for use under Mil-DTL-81706.  The third document (Mil-C-5541) specifies the performance characteristics of chemical conversion films on aluminum.

 

     Mil-DTL-81706 was revised on 25 October, 2004.  This revision now allows for non-hexavalent chemicals.  Mil-C-5541 is currently under revision to allow for non-hexavalent coatings.  One chemical, Trivalent Chromium Pretreatment (TCP), which was developed by the Navy, was licensed to four commercial vendors; CST SurTec, Metalast, Henkel Surface Technologies and Luster-On.  The commercially licensed versions of TCP are currently being tested for inclusion in Mil-QPL-81706.  It should be noted the Henkle version is Alodine 5900T and is not listed on their website.

 

     TCP appears to provide good paint adhesion and corrosion protection on bare aluminum (a traditional Class 1A coating under Mil-C-5541).  It at the same time provides a low electrical resistance coating (a traditional Class 3 coating under Mil-C-5541).  TCP will pass a bare (no other coating) salt spray test under ASTM-B117 unlike other non-hexavalent alternatives which REQUIRE a paint coating to promote corrosion protection.

 

     One of the issues regarding non-hexavalent alternatives centers around color.  TCP is for the most part colorless.  If you see any color at all, it may appear as a tinge of brown.  Other non-hex coatings are for the most part colorless as well and if you do see color it will again be a tinge from brown to purple, depending on the alloy.  So why not just add a dye?  In conversations with numerous people who have worked with these chemistries, and in particular with TCP, as soon as you add color, it will fail a bare salt spray test.  Hexavalent chrome is the reason traditional chemfilms have color.

 

     It is our understanding, the inclusion of commercially licensed versions of TCP in Mil-QPL-81706 and the revision of Mil-C-5541 are both due for release soon.  It is also our understanding, SAE will follow suit regarding the use of non-hexavalent alternatives after the Mil documents are released.

 

 

 

LINKS

 

Hexavalent Chromium -
NIOSH Topic Page

 

OSHA News Release

 

Regulatory Text
to Final Rule

 

OSHA Final Rule

 

State & Federal
Legislative Issues

 

ADOBE FILES

 

Small Business Advocacy
Review Panel Report to OSHA

 

EU Directive 2002/95/EC (RoHS)

EU Directive 2000/53/EC (ELV)

EU Directive 2002/96/EC (WEEE)

 

JG-PP Non-Chromate
Aluminum Pretreatments

 

Non-Chromate Aluminum
Pretreatments Phase I Report<
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Non-Chromate Aluminum
Pretreatments Phase II Report

 

Mil-DTL-81706B

 

Mil-QPL-81706-16

 

Mil-C-5541E

 

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