GMW3359
GMW3359 - Revision / Edition: C Chg: Date: 09/00/07 NON-ELECTROLYTICALLY APPLIED ZINC RICH COATING
Material Description.
The material to this specification covers organic or inorganic zinc flake coating with and without organic topcoat. This coating system must be free of hexavalent chromium, with no hexavalent chromium 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 adsorption. Non-electrolytically applied zinc rich coating has high permeability, which allows effusion of hydrogen during curing which might have been absorbed during acid pickling.
Typical Applications.
This coating is suitable for externally and internally threaded parts (size greater than or equal to M6) and non-threaded ferrous parts where high level of corrosion protection and freedom from hydrogen embrittlement are required. This is not recommended for the following:
Bolts and nuts of sizes less than M6.
Parts with internal drive recess.
Against magnesium surfaces.
Loose washers of all sizes.
Parts where electrical conductivity is required.
Remarks.
Use of this coating system on 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 be performed before releasing this finish on any new application.