Cadmium Plating on Stainless Steels

Q. Our company plates cadmium on PH stainless steels (17-4, 15-5). Problems with poor adhesion on these materials seem to be a frequent occurrence. We do not have these adhesion problems when plating on low-alloy steels. We use a cadmium sulfate bath at 15–50 asf. Prior to plating, we use a cleaning/activation cycle consisting of the following steps:

• Solvent clean as necessary.
• Aqueous degrease for 10 minutes at 140oF.
• Rinse in hot water at 120oF.
• Anodic clean for 10 minutes at 175oF.
• Rinse in hot water at 120oF.
• Rinse in cold water to cool the parts.
• Dip in 50-percent hydrochloric acid for 30 sec.
• Rinse in cold water.

Do you have any suggestions to minimize our adhesion problems?— J.C.

A. There are a number of things you can try to improve your activation process. One suggestion is to replace the 50-percent HCl dip with an acid dip consisting of 1 mL of hydrochloric acid and 10 mL of sulfuric acid in 1 L of water at room temperature. Immersion time should be in the range of 30–60 sec.

A number of cathodic treatments can successfully be used instead of the acid dip. One such process uses a 5–50-percent sulfuric bath at room temperature. The parts are made cathodicm and a current density of 5 asf is used for a period of 1–5 minutes. 

The most reliable activation process and the one I always recommend is to use a Wood’s nickel strike, which has a bath consisting of 250 g nickel chloride, 125 mL concentrated hydrochloric acid and 1 L water. The strike bath is used at room temperature with the parts being made cathodic at a current density of 35–50 asf for 2–4 minutes.

Additional suggestions for activation of stainless steels can be found in the book, “Electroplating Engineering Handbook, Fourth Edition,” by Lawrence J. Durney. The book is available from Amazon.com and is a bit pricey, but it is an essential addition to an electroplater’s library.