Zinc Plate on Zinc Die Castings
How can we prevent zinc die cast parts from changing color after zinc plating?
Q. We have a customer that requires zinc plate on a zinc die cast. The process seems simple and straightforward, but six to 12 months after the plating is completed, the parts change color, usually to a bluish color. Our customer finds this unacceptable and is demanding that we replace all of these defective parts. What can we do so this problem won’t happen again?— M.L.
A. I addressed this problem in one of my earliest columns. Here is essentially what I wrote at that time:
What you have is a diffusion problem, which can be common when one metal is plated over a different base metal but is rarely thought to be a problem when plating zinc over zinc die cast. The consistency of the zinc die cast is different from the zinc electroplate, and, as a result, the plated layer will diffuse into the die cast and produce a change in color.
The solution to this problem is easy. A diffusion barrier layer must be used on the zinc die cast parts. Most shops used a cyanide-based copper strike for this step, producing a copper coating that is least 0.3–0.5 mil thick.
Related Content
-
Products Finishing Reveals 2023 Qualifying Top Shops
Each year PF conducts its Top Shops Benchmarking Survey, offering shops a tool to better understand their overall performance in the industry. The program also recognizes shops that meet a set of criteria to qualify as Top Shops.
-
How to Choose Between Sulfate and Chloride-Based Trivalent Chromium
There are several factors to consider when choosing between sulfate and chloride-based baths for trivalent chromium plating. Mark Schario of Columbia Chemical discusses the differences and what platers should keep in mind when evaluating options.
-
Nanotechnology Start-up Develops Gold Plating Replacement
Ag-Nano System LLC introduces a new method of electroplating based on golden silver nanoparticles aimed at replacing gold plating used in electrical circuits.
