[Healeys] Healeys] Boot pan to shroud

[Bob Spidell]

Agree on the galvanic scale stuff, so I was surprised--and delighted--that my shroud Al was perfectly intact. 

Another factor is that bare aluminium instantly forms an oxide layer when exposed to oxygen (anodizing is a form of oxidation). The oxide layer is an excellent metal protectant, so even though the Al should corrode faster than the steel, the oxide layer protects it. I suspect the aluminium parts of a Healey sat around before installation and had plenty of time to form an oxide layer (and you can bet the assemblers wouldn't bother to clean it off before attaching to the cars). Our BN2's Al flanges are in good shape as well, though I have seen pictures of cars where they are all but gone. 

This is also why Al is often welded with a TIG welder on alternating current--half of the current cycle cleans the oxide layer off the surface and the other half of the cycle does the actual welding. 


bs 

-------------------------------- 
Bob Spidell - San Jose, CA 


Jaap, the word "weakest" in your response can be interpreted as meaning the 
material that is structurally less strong. Comparing aluminium/aluminum to 
steel, yes, it is structurally weaker. But what causes the 
aluminium/aluminum to corrode rather than the steel is that it is higher on 
the galvanic scale than steel and therefore more anodic. When two metals 
are in contact with each other in the presence of an electrolyte (like 
moisture), the more anodic will corrode first. 
Lead is structurally weaker than aluminum, but in an aluminum/lead joint, 
the aluminum is still more anodic and will corrode first. 

And "rust" is just a special term for corrosion on iron and steel. 

Steve Byers 
HBJ8L/36666 
BJ8 Registry 
Havelock, NC USA