Letter 19078

Anodic Cleaning - Formation of Oxide Layer?  

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Gents:

Thanks for the reply on my earlier question regarding additives to Anodic Cleaning baths.

I now have a follow-up question...

Background:
There is a "Quality Project" afoot that suggests the use of Anodic Cleaning to remove surface oxides from Inconel 718 (a precipitation-hardenable aerospace nickel alloy). The purpose of removing the oxide layer is to ensure the quality of subsequent welds meet spec (the facility I work in makes parts to aerospace quality standards)...we have intermittent weld quality problems due to inadequate surface preparation (i.e. residual oxide layer not removed during "other" surface preparation methods).

I am concerned that the production of oxygen at the anode during Anodic Cleaning will make the oxide layer even thicker than already exists on the parts (the detail components are procured from another shop) and therefore make subsequent welding even more difficult.

An additional note: our process calls out "alkaline anodic clean" as the first step, followed by "acidic anodic clean."

Question: does the Anodic Cleaning process produce an oxide film on the part? If so, how can the thickness of the oxide layer be approximated? Thanks for the help.

Regards,

David Smith
- Beltsville, MD, USA

First, you must process the parts per the OEM specifications. Second, PWA, GE, RR and a couple of smaller aerospace firms offer a choice of process solutions and frequently a choice of process methods. You have only listed one. There has to be more. Check their standard practices book. Third, Anodic electroclean is not going to add enough of an oxide layer to be found by microscopic methods, The referee method. It also is not going to remove any oxide. Anodic acid etch needs to be handled with extreme care-NO frelancing by the cleaning room operator or you will have scrapped parts-sooner if not later. This does remove metal and oxides. Forth, a moderately standart weld prep includes an abrasive blast or a flap wheel surface prep. Finally, why do you say that the oxide layer is a cause of your weld failures??? The vanadium in the alloy gives it very desireable properties and also makes it a bitch to weld by most welders that have not recieved specific training on that alloy. My money or coffee bets that you also have a microcracking problem that you just have not found. It takes a very good metallurgist to find it.

James Watts
- FL

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