This specification covers the requirements for tinzinc electroplate on steel substrates, with provisions for supplementary treatment. This plating is intended for corrosion resistance and electrical grounding purposes.

Material Description. The material approved to this specification is a Sn-Zn electroplate with passivation layer, plus a subsequent topcoat providing additional corrosion protection and consistent coefficient of friction.

Symbols. Not applicable.

Typical Applications. This coating is suitable for fasteners designated for electrical grounding purposes.

Note: This coating shall not be used for applications exceeding 195 °C during manufacture or in service.

Remarks. Use of this coating on threaded surfaces and/or bearing surfaces 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.

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

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