Ford WSS-M1P85-B1 Material Performance Specifications

The “Ford WSS-M1P85-B1 Material Performance Specification” standard, developed by Ford Motor Company (FORD), describes performance requirements for passivated, electrolytically coated zinc coatings on ferrous parts (such as stampings, forgings, and castings) that are threaded fasteners, some of which additionally contain overcoat sealants and where friction control is not required.

This standard was originally published to define performance requirements for electrolytically coated zinc coatings where corrosion protection or decorative appearance of ferrous surfaces is required. Parts may be rack or barrel coated and the plating bath chemistry (acid or alkaline) should be selected to provide the best performance in the application.

A trivalent chromium or chromium-free passivation treatment is applied to zinc-coated parts to retard the formation of white corrosion products. A thin-film passivation will maintain the silver color of the coating or impart a slight blue tint. Thick-film passivators impart an iridescent or colored appearance to the coating.

Sealants are applied to extend the corrosion protection of the coated part. Sealants can be organic or inorganic based, or a mixture of organic and inorganic components. Inorganic sealants generally exhibit better resistance to heat and degradation than organic sealants due to automotive fluids.

The WSS-M1P85-B1 standard is suitable for use on the body of white fittings and on painted parts after coating. The WSSM1P85-B2 and WSS-M1P85-B3 standards are suitable for the invisible interior or as a base coating for the exterior to be painted later. Passivation prevents the formation of white corrosion products during transport from the coating plant to the painting plant.

Only WSS-M1P85-B1, B2 or B3 standards should be used for parts that will be painted later. Not all passivations can be painted successfully, so part trials should be performed to verify paint adhesion to the passivations. Paint lines containing strong alkaline cleaners may remove passivations that would be acceptable if a pretreatment such as zinc phosphate was applied prior to painting. Sealants often prevent paint from adhering to the surface.

The requirements in the WSS-M1P85-B1 standard are described as follows:

• Approved sources: This standard is performance-based and does not have approved sources.
• Thickness: Based on “ASTM B659-90 Standard Guide for Measurement of Thickness of Metallic and Inorganic Coatings”, “ASTM B568-98 Standard Test Method for Measurement of Coating Thickness by X-Ray Spectrometry” and “ASTM B487-20 Standard Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopic Examination of Section”. The thickness is 1 µm min according to WSS-M85P1-B5 and 1 µm min according to WSS-M85P2-B3/B4/B5/B8. The minimum thickness applies to all major surfaces unless otherwise specified on the engineering drawing. If thick deposits adversely affect tolerances, functional requirements, installation or appearance, the maximum coating thickness shall be specified on the engineering drawing. In case of disagreement, the referee method for thickness measurement shall be the metallographic section according to ASTM B487.
• External appearance: Parts naturally have a silver or silver-blue appearance. When dyes are used to produce other colors, the color shall be specified on the engineering drawing.
• Coating adhesion: Based on “ASTM B571-18 Standard Practice for Qualitative Adhesion Testing of Metallic Coatings”. The coating shall withstand normal handling, storage and installation without flaking, peeling or other loss of adhesion. The adhesion of the electroplate to the base metal shall meet the requirements of one of the following test methods according to ASTM B571-18 unless otherwise specified on the engineering drawing:
  • Sharpening saw test: After the sharpening saw test, the electrolysis is not allowed to be lifted or peeled off from the substrate.
  • Polishing test: After the polishing test, the electroplating is not allowed to bubble, lift or peel off from the substrate.
• Laboratory accelerated cyclic corrosion test (CETP 00.00-L-467): Testing is carried out on coated parts (not panels) whenever possible. Parts to be tested should not have visible nonferrous corrosion products at the start of the test. Part orientation during the test should mimic in-vehicle component conditions, including spray direction, solution pool and, if possible, addition of matting compounds. Failure occurs when corrosion products are visible on critical surfaces or when corrosion products are spilled onto critical surfaces within the specified test range. Assessment is made without magnification at normal reading distance. Parts subsequently painted should be tested according to the paint requirements. Corrosion testing in the coated condition is not required when the part is subsequently painted.
  • Possible assembly damage: Assembly of components into a vehicle may cause damage to the coating. Whenever possible, assembly damage should be simulated before starting corrosion testing.
  • Exceptions: Depending on the location of the part on the vehicle, exceptions to this requirement may apply for certain applications. All exceptions are listed in the standard “Global engineering for total vehicle corrosion resistance 18-0040” and are shown in the photographic evaluation guide in the appendix to the standard.
• Embrittlement: Parts coated to this standard shall be free from the detrimental effects of hydrogen embrittlement or other factors that cause embrittlement of the part. All parts shall meet the requirements of the WSS-M99A3-A standard.

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