Summary for zinc-cobalt plating Discussion
zinc-cobalt plating on 6061-T6 aluminum was failing white-rust testing within 96 hours when parts were heated to 150 °C before salt spray, even though the same parts passed if they were not heated. Ted Mooney noted that the original target of 96 hours to white rust and 500 hours to red rust sounded reasonable, and asked whether the process vendor was helping with the zinc-cobalt bath and chromate. Vijendran suggested adding an inorganic sealant dip after passivation and allowing 24 hours to cure before heating, accepting some added cost. Kamlesh Bhatt later reported that switching the undercoat to high-phos electroless nickel improved results, with samples passing 96 hours after 50 hours of curing. When he asked about cobalt concentration, Ted said he was not a bath formulator and suggested sticking with proprietary electroless nickel baths. Ted also cautioned that zinc-alloy plating often needs chromates specifically matched to the alloy, not plain zinc chromates.
March 2, 2012
Q. Dear Sir,
We are in connectors manufacturing. We have a requirement of zinc-cobalt plating with 500 hrs of salt spray test. We are plating over aluminium, electroless nickel as base coat 4-5 microns, and zinc cobalt overcoat 12-14 microns, with olive green passivation. Aluminium grade 6061 T6
Specification: No white corrosion for 96 hrs and no base metal exposure after 500 hrs. Components should be heated to 150 degree for 1 hr prior to SST.
Components show white rust within 96 hrs of test. If we do not heat the component, the test passes. But during assembly line we will have to heat the component. Please give your valuable suggestions.
Thanks,
kamlesh bhatt
Manager Plating – PUNE, MAHARASTRA, INDIA
A. Hi, Kanlesh.
Please try to let the chromate cure for 24 hours before the heating and see what happens.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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March 2, 2012
A. Hi
Added to Mr. Ted ‘s suggestion you can try introducing an inorganic sealant dip after passivation process and let allow for 24 hours to cure before heating the components.
(Of course, slight increase of cost will be there, but your problem can be solved)
Good Luck.
Vijendran
Pune, India
Vijendran
– Pune, India
First of two simultaneous responses — March 10, 2012
Q. Dear Ted Mooney,
Thanks for reply. I have changed undercoat of high phos and submitted after 50 hrs of curing sample passes last week with 96 hrs. Same trials I am repeating and let you know. What is role of concentration of cobalt? We are maintaining 900 PPM. What is your suggestion for our requirement?
Thanks,
K.M.Bhatt.
KAMLESH BHATT
– PUNE, MAHARASTRA, NDIA
Second of two simultaneous responses — March 10, 2012
A. Hi, Kamlesh. I am not a formulator of plating baths and cannot answer your question. But I think you may be best served by sticking with proprietary electroless nickel baths as well.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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March 12, 2012
Dear Sir,
We have taken trials but results are not consistent. If we put for SST without heating it passes 350 hrs without any problem. But if we heat the components 150° then it may fail within 48 hrs. This components have another test of humidity with cyclic test.
Pl. suggest your comments.
Thanks,
K.M.Bhatt.
kamlesh bhatt
– PUNE/MAHARASTRA/INDIA
April 14, 2012
A. Hi, Kamlesh. It isn’t clear whether you are saying that you have tried all the things that were suggested, and these are you new results, or whether you just blew it all off and posted the same question :-)
Please clarify which if any of the posted suggestions you have followed. Thanks!
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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April 14, 2012
April 15, 2012
Dear Sir,
We have carried out SST after 48 hrs room temperature. Heating at 150 also after 48 hrs only. Generally after 48 hrs room temperature, how many hrs it should pass.
Thanks,
K.M.Bhatt.
kamlesh bhatt
– PUNE/MAHARASTRA/INDIA
A. Hi,Kamlesh. Your initially quoted spec of 96 hours to white rust and 500 hours to red rust sounds reasonable to me. Are you getting help from the process vendor who is supplying the zinc-cobalt process and the chromate? Generally, zinc alloy plating solutions require special chromates tailored to them rather than to plain zinc plating.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
April 15, 2012