Stainless steel and aluminium

March 5, 2008

I am a retired Civil Engineer and keep myself busy by making a variety of things. This can involve carpentry, small building works, restoration of just about anything and also inventing and making devices - usually for boats since I have a love of them having spent my early life closely connected with them in the UK.

Currently I am making a mast raising device for a second yacht as well as a second boat-launching dolly. The first one was a combination of wood and aluminum. This one is made of aluminium box tubing with some timber attachments. The dolly is for a small catamaran. For the wheels I want to use a 25 mm stainless steel round bar inside a aluminium tube which forms the axle. The round bar is a comfortable, but not tight, fit inside the tube. What should I do to prevent reaction between the dissimilar metals? I hope that I ihave provided enough information for someone to formulate an answer.

This is my first attempt to seek advice so am not familiar with the protocol.

Nick

Nick Sweet
Retired Civil Engineer - Western Cape, South Africa

March 6, 2008

This design sounds like a recipe for corrosion. Any coating you might put on the aluminun would be worn through, and the aluminum will corrode, possibly binding up your mechanism.

The stainless steel will be fine, especially T316. Look for other materials for your tube - T316, bronze, teflon.

Jeffrey Holmes, CEF
- Spartanburg, SC, USA

March 16, 2008

I agree that putting the stainless bar in an aluminum tube is a recipe for corrosion — especially on a boat that may be exposed to salt environments. My first thought is, "DON'T DO IT!". My second thought, "If you do it, have a nylon sleeve between the SS & Aluminum.". On boats, corrosion control is always an issue. Having dissimilar metals in contact invites corrosion because of differing electron affinities. Simplest solution is to use parts made of the same metal. I recommend it STRONGLY.

Ron Cooley
- Hillsborough, North Carolina