Blisters on Zinc-Plated Steel
How can we eliminate blistering on steel parts?
Q. We are experiencing blistering on steel parts, which are put through the following sequence:
1. Clean
2. Zinc plate
3. Trivalent chromium conversion coating
4. Bake for 12 hours.
Do you have any suggestions for how to eliminate the blistering?— M.U.
A. You do not state the type of zinc plating bath you are using, but I’m assuming it is an acid-zinc-type plating bath to minimize the formation of hydrogen during the plating process. There are a number causes for the formation of blisters. The most common, of course, is inadequate cleaning of the steel surface prior to the plating step. But, assuming you have a good cleaning sequence in place, where else should you investigate?
Do you see signs of blisters after the plating step but prior to the chemical conversion step? If no, the blisters are probably due to your baking step. If during the plating step excessive amounts of hydrogen are liberated, some of this hydrogen is trapped under the zinc plate. Baking of the parts is designed to reduce the amount of hydrogen present at or near the surface of the part. Baking the parts for a period of time does drive off the hydrogen, but the hydrogen escaping through the plate may cause blisters to form. Of course, if you are using a cyanide or non-cyanide-based alkaline bath you will generate more hydrogen during the plating step.
Related Content
-
An Overview of Electroless Nickel Plating
By definition, electroless plating is metal deposition by a controlled chemical reaction.
-
How to Maximize Nickel Plating Performance
The advantages of boric acid-free nickel plating include allowing manufacturers who utilize nickel plating to keep up the ever-changing regulatory policies and support sustainability efforts.
-
Trivalent Chrome Overview
As the finishing industry begins to move away from the use of hexavalent chromium to trivalent chromium, what factors should finishers consider as they make new investments? Mark Schario, chief technology officer for Columbia Chemical offers a helpful overview of this complicated topic.
