GMW4707

Description / Abstract: This specification covers requirements for a non-oily corrosion-protective coating consisting of zinc electroplate and subsequent aluminum-rich topcoat.

Material Description. The material and process approved to this specification is zinc electroplate on a steel substrate, followed by an aluminum-rich topcoat applied by dipspin method.

Symbols. Not applicable.

Typical Applications. The coating is suitable for internally and externally threaded and nonthreaded ferrous parts where a high level of corrosion protection and chip resistance of the coating is required.

Remarks.

Use of this coating system on the 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.

This coating requires the part to undergo a high-temperature curing operation. Parts heat-treated and not tempered, or tempered at a temperature below 175 °C may result in a drop in mechanical properties; therefore, proper precautions must be taken.

This coating system must be free of hexavalent chromium with no hexavalent chromium in the final product per the requirements of GMW3059. GMW3034 shall be used as a referee test.

Due to the risk of hydrogen embrittlement, electroplating parts with maximum hardness higher than HRC 48 is not recommended.