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DaBrainFarts t1_jb2j4gs wrote

Reply to comment by Flaxatron in Does galvanic corrosion take place when aluminum bronze is in contact with steel? by UserNo485929294774

Don't forget, depending on the steel, it can be its own galvanic cell. Fe2O3 and Fe3O4 are just different enough to make a anode-cathode pair.

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Agouti t1_jb3vlvv wrote

Yup, and it's also the mechanism behind pitting in stainless steel (chrome oxide as the anode to chromium steel) and galvanised steel (zinc as the anode to plain steel). It's why rust grows exponentially like a cancer, and why you want to stop it as quickly as possible.

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nill0c t1_jb4rpty wrote

I’ve always heard that the zinc on galvanized steels is a sacrificial coating, so you basically expect it to fail in the long run.

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ScreamingSeagull t1_jb514hw wrote

Yeah zinc, magnesium and aluminum are typically used as sacrificial metals for cathodic protection systems which is what a zinc coating acts as. At least from my limited understanding of corrosion.

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Agouti t1_jb8b223 wrote

It should only fail if there's a galvanic cell or if it's exposed to chlorine (e.g. sea water). We used to have galvanized fence wire that's easily 20 years old in the weather without any rust, but also had star pickets that were covered in rust in 12 months.

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nill0c t1_jbbnvtd wrote

20 years should be fine, we have some galvanized fence in a hedge that's from around 1960. It's pretty rusty now, but I'm sure it would have vanished by now if it wasn't protected.

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