INTERN MPAPS G-22 PDF

This specification covers mechanical, chemical, and physical property requirements and test methods, appearance requirements, quality requirements, qualification requirements, source approval and process quality control requirements, shipping and handling requirements, and requirements for designation on drawings for zinc-nickel coating systems on steel substrates that are free of hexavalent chromium.

APPLICATION

Zinc-nickel plating is used primarily to increase corrosion resistance of ferrous metal parts (fasteners, fittings, clips, brackets, etc.) where corrosion resistance greater than standard zinc plating is required. The alkaline zinc-nickel plating process, rather than acid zinc-nickel plating, is preferred for parts supplied to this specification, since it provides better coating ductility, minimal flaking, and higher corrosion resistance. A trivalent chromium passivate is applied to the zinc-nickel plating to increase performance. Supplementary sealers/topcoats may be applied, depending on the specified plating class and performance requirements. Plated parts should not contact a stressed component made of polyamides 6 or 66 (Nylon), due to the potential for environmental stress cracking in polyamides caused by corrosion products that form on zinc-based coatings in the presence of road salts. The service temperature range of zinc-nickel plated parts is -50 to 120◦C (-58 to 248◦F). This coating is not intended for electrical grounding applications, instead see MPAPS G-23.