Classic Mustangs List Archive

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Mail From: wal (Wal Marshall)

> Intergranular corrosion? Can you tell us more about this?

Im not sure about headers, but intergranular corrosion can occur when two different metals are mixed (alloyed). The two types of metal tend to form tiny grains within the metal structure, and corrosion occurs along these grain boundaries.

Common examples are aluminium alloyed with copper. Produces a very strong alloy, but the two are fundamentally incompatible (from a corrosion perspective) and over time the metal literally crumbles apart as corrosion works its way along the grain boundaries. Zinc with a little aluminium alloyed into it is another example Ive come across that eventually falls apart for the same reason.

I would have thought that most steel pipes used for headers would be pretty much homogenoius. However if intergranular corrosion was occuring the effect would be to slowly weaken the metal, and make it more brittle. It shouldnt get harder though...softer if anything..

Wal Marshall
www.nzmustang.com
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