GMNA GM7112M PDF

This specification covers the basic requirements for a nonoily corrosion protective coating consisting of zinc phosphate treatment, black zinc rich inorganic resin coating and black organic top coat.

Material Description. The coating system is free of hexavalent chromate, with no hexavalent chromate in final product per GMW3059 requirements. GMW3034 will be used as a referee test. This coating process does not generate hydrogen, however, pretreatment processes i.e. acid pickling could cause hydrogen absorption. Nonelectrolytically applied zinc rich coating has high permeability, which allows effusion of hydrogen during curing that might have been absorbed during acid pickling.

Use of this finish on threaded surfaces and/or bearing surface of joints could affect the torquetension relationship. It is recommended that a torque- tension study of the fastener joint be performed before releasing this finish on a new application.