Cadmium Plating Alternatives

Current Usage 

Cadmium plating is used for two primary purposes:
1. To provide sacrificial corrosion protection to steel components.
2. To provide galvanic compatibility between electronegative materials such as Al and Mg, and more noble materials such as stainless steels.
Cd plate is normally chromated with a typical hexavalent chromium conversion coating.
ConnyCyl3
Bolts
Common Applications Versions of Cd Plate Specifications

Corrosion Protection

  • High strength steel landing gear
  • High strength steel actuators
  • Steel fasteners (bolts, rivets)
  • Electrical connector shells

Galvanic Compatibility

  • Stainless steel actuators, sensors
  • Rivets for AL aircraft skins
  • Bright Cd for low strength components
  • LHE (low hydrogen embrittlement) Cd and TiCd  for high strength steels
  • Brush Cd for touch-up and repair
  • MIL-STD-870B (inactive)
  • MIL-STD-1500 (LHE Cd, inactive)
  • AMS 2401 (LHE Cd, inactive)
  • QQ-P-416
  • MIL-C-8837B vacuum Cd
  • AMS-C-8837 vacuum Cd
  • AMS 14198·79 (TiCd)

ESOH Issues
Cd is a heavy metal cumulative poison and a probable (Class B1) carcinogen.  Cd plating chemistry involves the use of several toxins.  Cd is deposited from a cyanide bath and post-treated with chromate sealant.  Cd, chromate, and cyanides are all heavily regulated because of their toxicity.  Cd regulations:

  • EPA: Limit 5ppb in drinking water
  • OSHA:  Cd PEL is currently 0.1mgm-3 for fumes, 0.2mgm-3 for dust
  • European rules (ELV, WEEE, RoHS):  0.01wt% limit in electrical and electronic products and vehicles
  • European REACH:  Cd plate not permitted on many products, including vehicles; except aircraft, electrical contacts, and critical safety equipment
  • Requires chromate passivation (European REACH and RoHS restrictions)

Exposure 
Personnel may be exposed during manufacture, depot overhaul, and operational level touch-up and repair.

  • OEM and depot personnel may be exposed to Cd and As in liquids and mists used in plating and to Cr6+ in chromating processes.   Emission controls, PPE required.
  • Maintainers are exposed in corrosion control and localized touch-up (brush Cd).  PPE required.
  • Cd can be leached during washdown of systems containing Cd-plated components (e.g., engines), producing hazardous waste

Alternatives, Applications, Status
Various alternatives are in production for different military and commercial applications. All of these alternatives are commercially available with the exception of the LHE ZnNi, for which the chemistry is available, but not the supply chain. However, LHE ZnNi is looking like the closest to a drop-in replacement, except for electrical connectors, where the material does not pass conductivity testing unless it is chromate passivated.

Most Common Cd Alternatives Examples of Authorizations and Implementations Specifications
Corrosion-resistant (CRES) materials – stainless steels, Ti, composites Engine components, fasteners, connectors Various
IVD Al (Ivadizing), pure evaporated Al Used by OEMs and several depots MIL-DTL-83488B
Electroplated Al (AlumiPlate) F-22, F-35 landing gear and other structural components, connectors MIL-DTL-83488B
Arc or flame sprayed Al Bombardier Dash 8 MIL-DTL-83488B
Metallic-ceramic coatings (e.g., SermeTel and equivalents), non-embrittling formulations Initially used on F-22 landing gear MIL-C-81751C
Zn- and Al-filled spray and dip-spin paints and ceramics Commercial automotive fasteners Numerous automobile manufacturers
Acid ZnNi Suitable only for low strength alloys (<160ksi) as embrittles. Permitted for electrical connectors AMS 2417E
MIL-DTL-38999 and other connector specs
LHE alkaline Zn(14-16%)Ni Qualified by Hill AFB for landing gear. Best results with trivalent passivation. Permitted for electrical connectors – must be chromate passivated Local Hill AFB spec. Commercial specs under development. MIL-DTL-38999 and other connector specs permit ZnNi
Electroless Ni-PTFE (electrical connectors only) Permitted for electrical connectors. Galvanically dissimilar to Cd MIL-DTL-38999 and other connector specs