GMW15821

Description / Abstract: This specification covers manganese-iron phosphate coating on ferrous metal. The coating may be impregnated with oil or another supplemental coating.

Material Description. A friable manganese-iron phosphate layer on a ferrous substrate is produced by a chemical process. Subsequent treatments can be added to enhance various other properties. A code system is provided in Table 1 for designation of these treatments.

Symbols. Not applicable.

Applicability. The primary purpose of this coating is for promoting rapid break-in of moving parts without scoring or scuffing, and provides minor corrosion resistance. Typical usage is on small moving parts with low corrosion requirements, such as certain powertrain components. This coating is also used on fasteners bearing against powdered metal components.

Remarks.

Use of this coating system 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.

This coating process generates a small amount of hydrogen in both the acid pickling and phosphating process. See 3.2 for precautions against hydrogen embrittlement.

The performance specified in this standard may not be met at elevated temperatures. Proper validation of material and process shall be performed before usage.

This coating process exposes parts to acids and may generate surface pits on metal surfaces. Generally, the higher the material hardness, the more severe the pitting. Ensure the coating process selected is not detrimental to the function or durability of the component.