Letter 14028

Galvanic couple between Al6061T6+Alodine1200 and AISI316L or AISI304L [France] 

We would like to know whether the aluminium alloy corrodes even with a Alodine1200 surface finish when in contact with stainless steel (time is 3 years, environment may be 95 Rh non condensing (storage period) and then ultra vacuum (functional period).

Ronan Le Letty
- Meylan, France

Is the stainless to be passivated?

Tom Pullizzi Platronica.com Falls Township, PA

The stainless steel is not passivated (standard screw made from AISI316L).

Ronan LE LETTY
- Grenoble, France

The galvanic couple between aluminum and stainless steels is low voltage. The natural oxide forms a fairly passive surface. However, passivating stainless steel would assure a uniform oxide. Chromate conversion coatings protect aluminum well, however, The chromate film is soft and thin, making it easy to penetrate. I expect that an anodized surface on the aluminum would be better, unless the force of contace with the stainless steel is large enough to penetrate the anodized surface.

Don Baudrand Don Baudrand, Consultant   Poulsbo, WA. USA

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