GMNA - GM6174M
Corrosion Protective Coatings Phosphate/Organic/Oil Type
| Organization: | GMNA |
| Publication Date: | 1 February 2005 |
| Status: | inactive |
| Page Count: | 2 |
scope:
This specification covers basic requirements for a black corrosion protective coating which is produced in a process consisting of zinc phosphate treatment, chromic acid rinse or seal, organic coating, oven bake, water and oil emulsion post treatment and air dry.
Material Description. At present the suppliers of this specification
provide coatings with
hexavalent chromate and some without hexavalent chromate. All Chemical
Suppliers/Applicator
Parts supplied to this specification shall be free of hexavalent chromate effective July 2005 or model year 2006 parts whichever is earlier.
This coating is especially suitable for bolts, clips and other small ferrous parts where above normal levels of corrosion protection, freedom from hydrogen embrittlement and decorative black color are desired.
Parts that are not suitable for barrel processing may be racked but must be processed through the same black organic coating employed in the barrel process.
Typical Applications. The organic coating is applied by barrel processing or racking over properly zinc phosphated small parts. Parts from either process are oven cured at 200°C for a minimum of 18 minutes. Immediately following the cure, the parts are immersed in a corporation approved protective oil compound in concentrations, temperatures and immersion times specified by the approved chemical manufacturer. The process is completed when packaged or placed in suitable confined containers.
Use of this finish threaded surface and/or bearing surface of joints could affect the torque-tension relationship. It is recommended that a torque-tension study of the fastener joint should be performed before releasing this finish on a new application.
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