In the April Plating Clinic column, I briefly discussed the differences between acid and alkaline non-cyanide zinc plating baths. One of our loyal readers, Mark Rottschafer, e-mailed some additional comments regarding these two plating baths. My comments were as follows:
There are a number of differences between the two types of zinc plating baths you mentioned. Space does not allow a complete comparison between types, but here are a few differences.
Acid Zinc Type
Alkaline Non-Cyanide Type
|Bright deposit - Reasonable substitute for bright nickel||Lower brightness compared to acid zinc bath. Parts are usually chromated after plating. Deposit is darker than other zinc deposits.|
|Excellent leveling ability||Poor leveling ability|
|Minimal hydrogen embrittlement||Lower efficiencies - More likely to have hydrogen embrittlement problems.|
|Poorer ductility especially in thicker deposits||Deposits have less ductility than any other zinc deposit.|
As you can see, the two types of zinc finishes are not completely interchangeable. You, as the customer, have to decide which properties are of the most importance to you and than sit down and have a discussion with you plating vendor.
You can find additional information on zinc plating by going to www.pfonline.com and searching the database for articles on zinc plating. A book, which is very detailed, is also available: Zinc Plating by Herb Geduld. The book is available from Metal Finishing Publications, 212-633-3199.
Mark suggested that two of the most important advantages of the alkaline non-cyanide plating bath are: 1) Much better thickness distribution over the surface of the part (particularly three-dimensional parts); and 2) Better acceptance of the heavier, darker chromates.