Cadmium has been one of the top choices for corrosion resistant coatings in aerospace, electrical, and fastener industries due to its excellent corrosion resistance, lubricity, electrical conductivity, and an ability to withstand thermal and electrical shock. However, cadmium is a known carcinogen, and it is deposited from a cyanide plating bath, and cyanide waste treatment¹ is very expensive. These environmental concerns and performance limitations mandate the need for alternatives to cadmium coatings. Numerous efforts have been made worldwide to develop alternate, non-cyanide baths for cadmium plating, based on sulfamate, fluoroborate and chloride.^2,3,4 Therefore, Cd replacement alternatives are being investigated to satisfy mission critical performance standards. Of these replacements, Ni-Fluorocarbon (SAE AMS-2454), Zinc-Nickel (ASTM B841, AMS 2417), Aluminum (Mil-DTL-83488), Zn, and Tin-Zinc have been recently evaluated. Each of these potential Cd replacements have shown potential to replace Cd for specific applications but only alkaline Zn-Ni has shown the most promise due to its conductivity, corrosion resistance, low hydrogen embrittlement (LHE), and the lack of cyanide and borate in the electrolyte.

This paper will discuss ongoing efforts by Faraday to optimize the deposition conditions for an adherent LHE Zn-Ni alloy coating on aluminum and steel connector surfaces. We will present data on the performance of the alkaline ZnNi process using direct current baseline conditions, while also evaluating the potential to improve coating properties using pulse reverse plating parameters. Specifically, our focus is on improving adhesion of the coating to the substrate, reduction of hydrogen embrittlement challenges, characterization of the functional properties of the coatings, and development of a preliminary technology transition plan. The following material property tests may be evaluated over the course of the program: 1) visual examination (AMS 2460), 2) thickness (ASTM B487 / AMS 2460), 3) adhesion (ASTM B571), 4) hydrogen embrittlement (ASTM F519), 5) corrosion (ASTM B117). This work will help facilitate adoption of alkaline Zn-Ni plating processes as a functional Cd replace for coating DoD mission critical components like electrical connectors and back-shells.

Acknowledgement

This material is based upon work supported by an SBIR from the US Air Force under Grant No. FA8501-16-P-0047 References:

1 W. H. Safranek, Plat. Surf. Finish., 84(8), 45 (1997).

2 D. Altura, F. Mansfield and L. P. Streett, Plating, 61, 850 (Sept., 1974).

3 A. J. Boehm , Plat., Surf. Finish., 80, 52 (1970).

4 James A. Bates, Plat. Surf. Finish., 4, 36 (1994).