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Silver Plating on Aluminum: Blister/Bubble/Peeling Problems
Q. We are carry out silver plating on aluminum gravity die casting. The process steps are Degreasing, Pre-cleaning, Zincating twice, Copper under coat of 5 micron, silver strike & final silver plating of 15-20 microns. All plating baths are cyanide base.
After plating the part is heated to 120 deg. cent for 1 hr for adhesion test.
Visual observation after preheating doesn't show any blisters on the plated surface.
Preheated part shows blisters after 2 to 3 days.
What could be reason that blister appear after 2 -3 days!
Is part preheated before silver plating!
Hemant Shah
switchgear industry - Vadodara, Gujarat, India
September 16, 2021
⇩ Closely related postings, oldest first ⇩
Q. We routinely manufacture machined Al 6061 and silver plate with no problems. But, when we go to cast parts, the plating does not survive a 250 °F bake without completely blistering. Currently we use an undercoat of zincate, a coat of copper and finally silver. We cannot tolerate nickel for electrical reasons.
Is there something special we need to do to cast parts to get better adhesion?
Richard Scott- Socorro, New Mexico
2001
A. We have a lot of experience plating silver on to cast aluminum for RF products. We do not use a nickel undercoat and do not have blistering after baking at much higher temperatures than 250 °F.
Brad Smith- Evansville, Indiana
Q. Hi Brad,
We have exactly the same problem Richard has. Can you please give me some more info how you solved the issue.
Your quick response would be appreciated.
I hope you still can get this e-mail to reply to an old issue dated 2001 :))
Thanks
Alex
telecommunication - Brisbane, QLD, Australia
2005
Q. Dear Sir,
Our subcontractor is trying hard to solve bubble problem when plating silver (Ag) on Aluminum plate, but failed several times -- the bubble usually comes out after drying procedure - heat chamber -150 °C.
Unfortunately, the plating work is the most important part of this project since the component will be used in the telecommunication field.
Would you please kindly instruct us some reasons that caused these bubbles?
Appreciate you help, and with best regards,
Tom Wu- Dong Guan City, Guang Dong Province, PRC
2002
A. Tom,
A lots of things can make the silver get bad adhesion on the aluminium surface.
1. Pretreatment steps.
2. Rinse steps.
3. Dirty acids, especially nitric acid can show micro bubbles if this solution is old and you have some contamination in it.
4. Low silver contents to the free cyanide in silver solution.
I think you must explain more how you do your pretreatment for us.
Regards,
Anders Sundman
4th Generation Surface Engineering
Consultant - Arvika,
Sweden
A. Hi Tom,
Aluminium being a very active metal (electrode potential -1.66v) is difficult to plate because of oxide film leading to non-adherent deposition. Pretreatment and undercoat are the two most vital aspects which need to be looked into for the blister formation you face after heat treatment. Ensure and try improving your pretreatment. Aluminium being an active metal, try immersion coating of zinc. Silver, a noble metal will need a undercoat of nickel followed with a strike .
Venkat Raja- Kitchener, Ontario, Canada
Q. Dear Sir , We are one of the silver platers in Bangalore and we are doing silver plating on Aluminum wherein we are always facing the problem of blisters. Out of a batch of 25 at least one gets rejected. Please let me know if I have any methods to ensure that blisters are not repetitive.
Regards,
Shreesha Acharya . Pplating shop - Bangalore, Karnataka, India
2004
A. The most probable source is a bad/poor zincate before the strike. Since you did not give us any information on your process, I will guess that you are not using a double zincate (zincate-strip-zincate) You may need to go to one of the proprietary ternary zincates. You might also check for excessive brightener in one ore more of the plating tanks. You might not be getting the parts clean enough or properly de-smutted/activated. Lots of possibilities.
James Watts- Navarre, Florida
Q. Hi All
Currently we are working on an RF amplifier which has an aluminum casing and we need to plate the casing by some means to be able to solder components onto the casing. From a local plating shop we plated some sample parts. The samples we plated
A) first copper (MIL-C-14550 [link is to free spec spec at Defense Logistics Agency, dla.mil]
B) and then silver (QQ-S-365
[from DLA]
).
But the silver plating peeled off when we removed masking tapes used during paint.
Could anyone suggest us another way of plating or where did we go wrong in our case?
Thanks
- Ankara, TURKEY
2005
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A. If the copper peeled off, then the parent metal either was not properly cleaned or properly activated (or both). If the silver peeled off of the copper, then the surface of the copper was the choice above or it was bright copper and had too much brightener.
Talk to your plater, he has a problem.
- Navarre, Florida
A. If you want any help on this you must give details about the plating process, preplate cycle etc.
Sara Michaeli
Tel-Aviv-Yafo, Israel
A. MIL-C-14550 B and QQ-S-365 have adhesion requirements (identical tests) which the plating seems to have failed. But, did you bake the paint at a temperature above 149 °C (300 °F)? QQ-S-365D, Paragraph 3.3.5 says higher temperatures weaken the adhesion of silver to copper. A barrier layer of nickel is required for long term use at higher temperatures. Do adhesion tests as-plated and after baking (if applicable).
As alternatives, consider matte tin plating or low-phosphorus electroless nickel (EN) plating the aluminum. With tin, if baking the paint, stay below 200 °C to avoid melting. With EN, it may be necessary to also silver plate, since baking can oxidize (passivate) the EN surface. But possibly, masking would protect the EN during baking.
- Goleta, California
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Q. Thanks for all the comments.
The paint was cured around 60 °C for one hour. I don't assume this created the problem. However we will also solder components onto this part by using vapor phase process, during which the parts will be exposed to temperatures above 200 °C. I think we should use Nickel undercoat.
- Ankara, TURKEY
2005
A. I use silver plating all the time for microwave RF housings that need to be solderable ... We specify a Sodium Zincate cleaning process followed by a copper underplate and then silver ... It's extremely rare (almost never) that we encounter any peeling of the plating ... I suspect you are not using a qualified or experienced plating vendor.
Bob Diamond- Hauppauge, New York
Q. Hi Again
In our second try, we first plated aluminum case with Nickel and then with Silver. The coating is mechanically fine, also it solders very well. My only concern is about thermal stress. Nickel is a brittle material -- could it cause thermal cracking problem after a number of thermal cycles?
Thanks
- Ankara, TURKEY
2005
A. Hi there.
I think we must have a answer of your first question to help you. Does the silver peel off from the copper plating and you can see the ground [substrate] metal or can you see the copper plating?
Nickel can be brittle due to the additives if they are not correct in your solution, but not if by heat treatment because if everything is correct the aluminium and the nickel will diffuse in a high temperature about 300 °C.
Regards,
Anders Sundman
4th Generation Surface Engineering
Consultant - Arvika,
Sweden
A. We have a silver plating shop for silver plating on wrought & cast aluminium. Precleaning & undercoat are the important process to prevent peel off.
Hemant Shah
switchgear industry - Vadodara, Gujarat, India
Q. We are plating 6061 alum with electroless nickel, copper and silver. we have to pass a 200 °C bake for 45 min and are having blisters show up after the bake. any suggestions?
Bob Gillinghamplant manager - Billerica, Massachusetts, USA
September 2, 2009
A. Sounds like cast rather than wrought material.
Unfortunately, you can over-clean and under-clean with the same net bad results. I would question your desmut step. Also, you have said nothing about a zincate step. I prefer a double zincate and the use of an alkaline electroless nickel strike.
- Navarre, Florida
A. 1. Consider the thermal expansion coefficients of the sandwiched metals.
2. Consider the thermal diffusion problems of the sandwiched metals. That copper will come right thru the silver and cause blistering. The copper should be UNDER the nickel or not at all, heated copper "walks" almost as bad as silver.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
Q. I am trying to do Silver Plating of one micron on my aluminium alloy having plated total area 5 m3 but the problem is that after plating when I heat them at the temperature of 300 °C, bubbles are formed. Now my customer is having problems with that; he says there should be no formation of bubbles when he heats it at about 300 °C
Please help to get this plating right so that after plating, upon heating there are no bubbles in holes.
plating shop employee - Kanchipuram, India
December 12, 2017
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