Cadmium Alternatives for High-Strength Steel

Abstract : Testing was conducted for cadmium alternative coating systems IAW the High Strength Steel Joint Test Protocol for Validation of Alternatives to Low Hydrogen Embrittlement Cadmium for High Strength Steel Landing Gear and Component Applications. Coatings suitable for full size components which were evaluated in this effort included sputtered Al, electroplated Al, LHE Zn-Ni, Acid Zn-Ni, and electroplated Sn-Zn which were compared against control coatings cadmium and IVD-Al. Repair coatings that were evaluated included brush plated Zn-Ni, brush plated Sn- Zn and spray/brush-applied SermeTel? 249/273. The control coating for repair was brush cadmium plating. The most promising candidates to replace cadmium plating included LHE Zn-Ni and electroplated Al which showed the most favorable balance of properties, although there are process specific reasons to consider the other coatings for certain applications. LHE Zn-Ni showed excellent corrosion resistance most similar to cadmium especially in the scribed (damaged) condition. In general, results showed that the aluminum based coatings perform well in corrosion fatigue, bend adhesion, paint adhesion, galvanic compatibility, and chemical strippability. The electroplated aluminum coating performed best in the various types of embrittlement and re-embrittlement tests conducted per the JTP.