Development of a New Electrodeposition Process for Plating of Zn-Ni-X (X = Cd, P) Alloys Permeation Characteristics of Zn-Ni-Cd Ternary Alloys

It is shown that an electrodeposited Zn-Ni-Cd alloy coating produced from sulfate electrolyte inhibits the discharge of hydrogen on carbon steel. The newly developed ternary alloys have approximately ten times higher corrosion resistance when compared to a Zn-Ni alloy. Hydrogen permeation characteristics of Zn-Ni-Cd alloy coatings were studied and compared with those of a bare and a Zn-Ni alloy coated steel. The transfer coefficient, $\alpha$, exchange current density, i o , thickness dependent adsorption-absorption rate constant, k″, recombination rate constant, k 3 , surface hydrogen coverage, $þeta$ H , were obtained by applying a mathematical model to experimental results. Alloys obtained from baths containing higher concentration than 3 g/L of CdSO 4 in the sulfate plating bath are seen to have superior permeation inhibition properties compared to the Zn-Ni alloy coating and bare steel. The hydrogen permeation current was zero under normal corroding conditions for Zn-Ni-Cd alloy and it increased to 0.3 $μ$A/cm 2 at a cathodic over-potential of 250 mV. The hydrogen permeation current density for steel and Zn-Ni alloy under similar conditions were 62.1 and 1.3 $μ$A/cm 2 , respectively.