Is There A Corrosion Expert Out There?
Sacrificial anodes protect steel boat hulls in water. Without submersion in
water I doubt the cathodic circuit is complete enough to protect against
corrosion caused by localized galvanic reactions in moist or temporarily wet
areas of a car body.
The aluminum panels will protect any steel they contact from corrosion by
sacrificing themselves. Aluminum is more active than steel. A scratch in
the coating on an aluminum panel under a steel washer as the steel nut &
bolt are tightened can become a focal point for corrosion if moisture is
regularly or continuously present. The exposed aluminum around the hole in
the aluminum panel will transfer ions to the steel parts, loosening the bolt
by pitting of the aluminum. A tack or nail holding an aluminum panel to
wood will loosen the same way if the coating seal is broken and moisture -
even humidity gets to the steel tack where it is contacting the aluminum.
Unless lead is a more active metal than aluminum, a lead anode will not
protect aluminum from corrosion. Magnesium or zinc anodes might be more
active metals than aluminum and thus more affective at protecting aluminum
from any contact points with steel.
The TF has an aluminum water outlet elbow between the engine and the upper
radiator hose. This elbow can become so corrosion pitted from the inside as
to leak. The holes in the elbow for the steel studs can become enlarged to
a point of weakening the seal on the gasket. This is due to the aluminum
sacrificing itself to the studs which also seem to corrode badly.
Electrically isolating the studs, nuts and washers from the aluminum elbow
with dielectric plastic pieces acquired from an electrical supply house will
eliminate the corrosion. The gasket and the radiator hose serve to complete
the electrical isolation of the elbow preventing further deterioration of
the aluminum
Sacrificial magnesium anodes in both the engine block and radiator that stay
wet continuously from the water in antifreeze will reduce corrosion of soft
plugs, radiator brass etc. Anodes on the car body are in my opinion
unlikely to protect against galvanic corrosion due to a lack of near
continuous moisture to complete the circuit. Might work though if one parks
in deep puddles.
Jon
-----Original Message-----
From: david.tinker [mailto:david.tinker@virgin.net]
Sent: Monday, April 24, 2000 3:55 PM
To: mg-t@autox.team.net
Cc: Sleuth@usa.com
Subject: TF Restoration.
Hi MGT Types,
You may remember the saga of my new TF body clad in aluminium alloy rather
that steel, and the response I had through the List on the subject of
dis-similar metals being in close contact and the possibility of subsequent
corrosion .
Well my friend Colin Gibson put me in touch with an Aircraft Engineer Peter
Tanulac, who made the following recommendations. That all mating parts ( ie
Ally/ steel) be coated with a paint called Duralac, which is used is similar
situations on light aircraft. Where POP rivets are used employ ally rivets.
He also advised the use of a Lead sacraficial annode approx 75 x 25 x 12mm )
and attached to the bare ally body( ie metal to metal contact ) and finished
with a wash/ etch primer. The annode is renewed when it disappears ,
probably in the after life!!!!!!!.
My considered opinion is that if it it good enough to fly in it is good
enough to ride in, and this is the proceedure to follow, ( unless you know
better ).
Keep MGing
David Tinker
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