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From: Bill Sheehan [email protected]
Date: 10 Jan 2003
Time: 14:54:53
Remote Name: 203.29.131.3
Hi Ron - point taken, but you missed a vital component in the equation - the elements of salt, water & air are what causes the electolyis if the 2 different metals are not insulated from each other, not the metals per se (although with the high content of chromium in s.s, it eventually succumbs on a yacht). For reasons yet unexplained, electrolysis in marine engines (caused by the salt water plus cavitation)is much more severe in the warmer Southern waters than anywhere else. The problem is minimised by suspending zinc rods in the water flow. Zinc. Thatis why I suggested etch primer (zinc chromate) plus plenty of coats of paint to insulate the steel from the aluminium & to keep moisture out. Also suggest you don't be too severe on "cleaning" the ali, as I assume you are using new aluminium in your Special. PURE ali is highly resistant to corrosion because of a thin film of aluminium oxide which always forms immediately when the metal is exposed to the air. This layer forms an almost impervious coating which is quite hard and is not subject to ordinary corrosion. With ali ALLOYS, because of the alloying metals contained in the aluminium, a pure coating of aluminium oxide cannot form on the surface - hence the alloy will corrode easily. To protect ali alloys from corrosion, a "cladding" process was developed. In this, a thin layer of pure aluminium is bonded to the surface of the alloy as the sheet is rolled. This layer gives the alloy sheet the same corrosion-resistance characteristics of pure-aluminium sheet. Good luck, Bill