Copper Etching - FeCl3/HCl/H2O 1

[SMF1964]

My Brackground:
I have a nickel-aluminum-bronze (cast) electrical bolt that contains a tin coating. The casting has a large number of casting voids in it (that resulted in failure when torqued). Examination of the casting porosity shows tin 'flakes' on the surface of the dendrites. I have a metallographic section through the porosity that I etched with ASTM 413, etchant 34B (5g FeCl3, 50ml HCl, 100ml H2O, activated with a few drops of nitric acid) and looking at the microstructure, I see no tin on the surface of the porosity.

My Question:
Will the etchant used dissolve the tin?

 

[Goahead]

The answer could possibly come by trying an alternative etching procedure. Metals Handbook 8th edition Vol. 7 shows at page 296 four micrographs with electrolytic etching in 1% chromic acid solution.
How can Tin from the plating coat the internal porosity?

http://www.welding-advisers.com/

 

[arunmrao]

It can be an open porosity on the surface. Why was a cast material suggested for a bolt application. Continuous cast rounds could have been used perhaps as the stock for making bolts.

 

[SMF1964]

More info:

It's an odd shape. Picture an eye-bolt, with two tabs coming off the top of the eye. The orientation is such that a neutral ground conductor passes through the eye and is secured to the eyebolt by what look like 'hose clamps' over the tabs. The threaded end of the bolt is secured somehow/somewhere - I only got the eye part.

Goahead: hexavalent chromium (such as chromic acid) has been banned from our lab as it is a carcinogen.

Arunmrao: That is my thinking, that the porosity was open to the surface somewhere. As to why a cast material was used - I can only speculate that since this is not a high stressed application, strength was not the critical issue, castings were cheaper.

 

[EdStainless]

How about trying 80ml H2O, 5ml H2SO4, 10ml potassium dichromate.
Yes, I know, chromate.

The other choice that I can think of is to use an electrolytic etch with 950ml water, 50ml H2SO4, 2g NaOH, and 12g iron sulfate. You will need about 9V for about 10-15s.

I take it that the bulk chemistry is OK?

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Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[SMF1964]

Bulk chemistry is acceptable. I will try the peroxide/NaOH/FeSO4 - any special safety concerns on the mixing of peroxide (acid) and hydroxide (base) in preparing this solution?

 

[EdStainless]

No problems, there is a lot of water. Just add the sulfuric slowly and then the caustic and sulfate. You should let it stand on a stir plate for a while to make sure that everything disolves.

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Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm