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Discussion Forums - The Hendrix Group
HomeHomeDiscussionsDiscussionsMaterial Select...Material Select...Galvanic corrosion of weld near Au plated areaGalvanic corrosion of weld near Au plated area
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1/14/2004 9:00 AM
 
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I laser weld Nickel plated Kovar (FeNiCo) lids on Gold plated Fe-Ni (%7E50/50) housings. Gold is removed from the housing surface for weld prep. The result is a fillet weld with Nickel plated Kovar on one side and Gold plated Fe-Ni on the other side. Of course the weld area is relatively small compared to the total housing/lid surface area. In salt fog tests the welds severely deteriorate after %7E 100 hours. I understand that the weld will always deteriorate faster than the base metal, but will the weld life be improved by eliminating the Gold plating on the housing or Nickel plating on the lid to reduce the Galvanic potential. Uniform corrosion on the relatively thick body is preferable to localized destruction of the .010" thick cover/weld area. Thanks, Bob
 
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1/19/2004 9:00 AM
 
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Bob: Thanks for your interest in our discussion forum. Your post is difficult to answer with the available details. We are not familiar with "Kovar". Specifically, what is the weld composition? It may not even be a galvanic issue. However, with your material combinations and galvanic corrosion principals, you would be reducing the galvanic potential by eliminating the gold. Hope this helps! David Hendrix The Hendrix Group Inc.
 
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1/20/2004 9:00 AM
 
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Thank you for your prompt and helpful response. Kovar is an FeNiCo alloy (%7E53-29-17). It is welded to Carpenter 49, Fe-Ni (%7E50-50). It seems that the gold plating will eliminate surface corrosion on the body, but will concentrate corrosion processes at the unplated weld area. Best Regards, Bob
 
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1/20/2004 9:00 AM
 
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Bob: Thanks for the "Kovar" clarification. Based on the Kovar vs. Carpenter 49 alloy composition we would not expect a significant potential difference between the two alloys; however, if one existed I would expect the Kovar to be slightly anodic to the Carpenter alloy. One could easily verify that with laboratory testing. Regarding the weld corrosion, Chromium is the essential element for imparting corrosion resistance to an alloy. Neither alloy contains Chromium, thus, the weld corrosion may be corroding due to inadequate corrosion resistance and the Gold plating simply protecting the base metal. If it is important to know the root cause, we can probably help you. David Hendrix The Hendrix Group Inc.
 
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