GMNA GM6174M PDF

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/Applicators, who are providing hexavalent chromate free coating shall submit to the GMNA Finish Committee the name of the chemicals currently used and a signed certificate that their coating system is free of hexavalent chromate, with no hexavalent chromate in the final product per GMW3059 requirements. GMW3034 will be used as a referee test.

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.