Metal finishing Q&As since 1989

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Having trouble plating 6061-T6 Al after plating it successfully for years

May 14, 2009

I've been the plating tech for 10 years at a company that does in-house plating of material used for industrial power distribution. We plate a wide variety of copper and aluminum ranging from 8.5" by 10' wide buss-bar to very small parts that fit in breaker panels. We bright acid tin plate 99% of material. (other 1% is silver) We use the Alstan process for our aluminum. Most of our aluminum is 6101-T6 which is for us a very easy material to plate. We introduced the 6061 alloy a few years ago because it was the "best" material for the new parts being introduced to the product line. Originally the parts were basically a triangle of varying sizes with the ends cut off and some square punch outs. When I first got the parts, they would not run on the settings that the 6101 ran. Got lots of peeling on edges of parts. To make a long story short, we found that about 10% sulfuric in the desmut, much longer in the 88c step of Alstan process, and lower current in bronze bath fixed the problem. I assume the steps had to be taken due to the higher level of magnesium in 6061 vs. 6101.( about double) we've had some material now for about two months that I can't get to plate. Edges are always ruff with small blisters on corners of parts. Worse on top parts. Dumped and remade every tank in Al process with the exception of Alstan baths. Cut bronze and 88c baths to freshen up. If you run current lower you get big contact blisters (titanium tips) and if run current up more of the same on edges. Can't seem to find a happy medium. Hardness in specs but material from new vendor. Can't seem to get QC to send material out for alloy check. Any suggestions?

Russell Emery
Plating Line Tech - Roebuck, SC, USA

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Seems the starting point to knowing the cause of the problem (a prerequisite to knowing the solution!) is with your QC people. First you must be sure what material you are dealing with. And if you still have some components from the previous supplier, a comparison would be useful.

Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.
May 18, 2009