GMW16730

Description / Abstract: Material Description. This finish is a bulk-applied finish for small ferrous parts. It consists of an electroplated zinc-nickel layer with passivation and topcoat.

Symbols. Not applicable.

Applicability. This coating is intended primarily for bulk-processed small steel parts, such as bolts, screws and nuts used on exterior and interior visible parts (cosmetic applications). The finish is especially suitable for internal drive (cross recess, hexalobular (six-lobed) socket, etc.) threaded fasteners and other parts with small recessed features. This specification covers requirements for a corrosion-resistant black finish for small parts.

Remarks. Electroplating may not be suitable for all materials and applications. Each application must be reviewed with the responsible Materials Engineer before usage.

Use of this coating system on threaded surfaces and/or bearing surfaces 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 any new application.

This finish is suitable for temperatures up to +120 °C. Applications with exposures above this temperature shall be reviewed with the responsible Materials Engineer before usage.

High-strength or high-hardness steel parts are susceptible to hydrogen embrittlement. While certain precautions and post-plate de-embrittlement baking are generally effective in protecting the parts from hydrogen embrittlement, they are time sensitive and require extra care during processing. Electroplating of steel parts with hardness above 46 HRc is not recommended.