Take a look at the article on the following web site. Read the portion on
corrosion. It may help
answer your question.
http://elvis.engr.wisc.edu/UER/uer99/author1/content.html
Jim Y
Steve:
Try searching on Google using the phrase "cathodic protection of
aluminum"(and aluminium).
Cathodic protection was applied to aluminum alloys over forty years
ago.
See: http://httd.njuct.edu.cn/MatWeb/soil/alsolccp.htm which
references NACE Recommended Practice 2M363.
The galvanic series for metals in soils:
http://www.corrosion-doctors.org/Aircraft/galvseri-soils.htm
and the series in flowing sea water:
http://www.corrosion-doctors.org/Aircraft/galvseri-fig.htm
both show that either magnesium or zinc are even more active than
aluminum and could be used as sacrificial anodes. In fact you can buy
zinc anodes designed specifically for mounting on ships.
See: http://www.mgduff.co.uk/Cathodic_Protection_for_aluminium_hulls.pdf
Unfortunately, automotive cathodic protection is a fatally flawed
concept, since you don't have a good way to protect the surface unless
you almost completely coat it (which is what is done with zinc on auto
body steel panels). See:
http://www.corrosion-doctors.org/Car/carCP.htm
The article referenced on the above site by the late Harry Webster
gleefully pointed out that orders of magnitude more current went into
the LED plot light on one device than went into protecting the car.
(Harry had been president of the National Association of Corrosion
Engineers and was an expert on cathodic protection. He testified as an
expert for the government in court in Ontario).
One product, Rust Evader, also got taken down by the U.S. government.
See:
http://www.ftc.gov/opa/1996/06/rust-id.htm
Subsequently they went offshore to Singapore, and, if you wish to :) ,
you can still buy one on eBay.
Pittsburgh Pete
------------------------------
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Landies aren't aluminium - they're mainly steel, with a few bits of
aluminium / magnesium alloy bodywork stuck on the top. For something
like a Rangie there's a third intermediate layer of a thin steel
bodyshell, between the heavy-gauge steel chassis and the aluminium
panels.
Corrosion protection for them is simple - use a factory galvanised
chassis. That's the part that fails expensively, that's the way to
protect it. For the common but replaceable failures (Rangie tailgate
frames, Landie doortops) then some form of paint-time zinc coating is
worth putting effort into, whether this is just a good zinc-rich
primer (like Davids 182) or even a metal-spraying process.
The "aluminium" bodywork doesn't suffer from corrosion - largely
because of the alloy used. Although this Birmabright alloy was chosen
for strategic reasons post-war (early Landies were literally made from
old Spitfires) and it was retained because of its stiffness, it's also
a good choice for corrosion resistance.
Zinc anodes, active protection systems etc. are fine, but you have to
dunk the vehicle in an electrolyte to really show any benefit. Good
for boats, bad for cars.
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