This specification covers the basic requirements for Sn-Zn electroplate on steel substrates mating to aluminum, steel and cast iron with provisions for supplementary treatments and corrosion resistance. This plating is intended for grounding purposes. Alloy composition shall be a range of 75 ± 10% Sn and the remainder Zn. Minimum recommended plating thickness shall be 8 µm. Higher or lower plating thickness may be specified at the discretion of the user.

Note: Verification of alloy composition shall be by XRF (X-ray Fluorescence) or AA (Atomic Absorption) using standards and procedure approved by the chemical supplier or equipment manufacturer.

Material Description. The material approved to this specification covers Sn-Zn electroplate plus a subsequent protective treatment. 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.

Symbols. Not applicable.

Typical Applications. This coating is suitable for fasteners designated for grounding purposes. In addition this coating may be used for fasteners M5 or smaller. 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.