plating, anodizing, & finishing Q&As since 1989
Blistering of silver/nickel on machined aluminum
We have an aluminum body (6082 T6) which is electroless nickel and silver plated.
The units are double zincate treated and then 2um of nickel and 4 µm of silver are applied.
The units undergo a reflow process where max temp for lead free processes reach 250 degrees for approx. 30 seconds peak. the units are blistering in two ways. Silver from the nickel but more predominantly nickel from the aluminum. The blistering is not confined to the features of the unit but spread over all planes.
All units undergo a soak process of 160 degrees for one hour as part of the plating process.
Known causes are contamination of the plating bath metal turn over or incorrect pre-treatment, greater than 100 ppm of zinc in the bath.
We use different suppliers for the same product but some batches are fine but some blister immediately.
Has anyone any experience of this? Are there some key elements that we can use to maintain the processes and stabilize the product What standard control need to be used as a minimum to regulate the baths?
Thanks in Advance.
If you see Nickel is peeling off from aluminum parts,Check E.Nickel M.T.O. Never Plate Aluminum parts more than 2 M.T.O
And Silver peeling off, Check Silver Strike.If Silver Strike is Old Make New Strike,or carbon treat Silver Strike.
Always aluminum parts in New E.Nickel Tank.
I can understand your problem. for Al component what type of desmuting solution your follow. if you use 90%of HNO3(70%VOLUME)+10%OF HF(40%VOLUME). It will give good result. Then check Ag strike bath. If it is very old please change it.
wish you good luck.
You did not mention a silver strike. You need one. You should have a nickel strike also. My choice is an alkaline EN which might be enough for the minimal thickness you have listed. It will take longer to build up. You have to get from the nickel to the rinse to the silver strike fast as nickel passivates rapidly .James Watts
If your using a phoshorous e'less nickel then I would use nickel boron. Better for thin coatings in microns and not porous, it goes passive quickly but you can keep the parts active with a ten per cent sulphuric solution. It is also possible to do the silver without the strike like this as long as its well rinsed.Chris Matthews
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