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Blade corrosion when the aluminum spacer between two blades(stainless steel )

In the common sense, when the aluminum touching with stainless steel, the aluminum will first corrosion....'cause it's more active. but in our case is just different, which the steel is first corrosion....y? it's quite abnormal. if the plastic spacer between two blade the corrosion will be much better! so I do believe issue is on the aluminum spacer....pls expert tell me y? and how to prevent? actually whether we pickling or not. this issue is always happen.

Jason Yang
engineer - China
April 9, 2008

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First of two simultaneous responses --

Nihao Jason,
What is the corrosion agent or substance? Aluminum is very resistant to oxidizing environments like nitric and chromic acid. It is not resistant to reducing agents like chlorides, fluorides and alkalies. If anodized it becomes non conductor.
Zai jian!
Hanyu Xueseng
Guillermo Marrufo-Monterrey, Mexico

Guillermo Marrufo
Monterrey, NL, Mexico
April 10, 2008

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Second of two simultaneous responses --

You have a galvanic couple betwen tyhe aluminium and the stainless steel, but in reality, the aluminium is covered in aluminium oxide, which has a higher redox potential. Corrosion then occurs on the stainless steel because the other electrode reaction is more electropostive. Hwnce, the electrode potential of the aluminium oxide reaction is more cathodic than that for stainless steel, so it is the steel that corrodes. Inserting a plastic space between the steel and the aluminium breaks the circuits, so you do not have a galvanic couple between the two metals and therefore no electrochemically induced corrosion

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
April 10, 2008