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Flaxatron t1_jb24iou wrote

Short answer: Yes.Long answer: Galvanic corrosion takes place when any two metals come in contact with each other. The severity depends on how cathodic/anodic they are in relation to each other. How aggressive the reaction is depends on how different their electrochemistry is, with the more anodic metal losing material or corroding.Steel is also a very broad category. Where a low alloy steel might corrode in contact with aluminum bronze, a bimetallic couple with stainless steel would cause the aluminum bronze to corrode.
Search for "galvanic series" charts to see where your materials end up to get a general idea of how they would react

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DaBrainFarts t1_jb2j4gs wrote

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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amagicalwizard t1_jb2u46h wrote

Just thought I'd add that it's not just metal to metal contact that can cause galvanic corrosion. When working with carbon fibre composites the nobility of metals that are in contact/inserted are of concern as they will likely galvanically corrode due to the conductivity of CFRP.

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Bunsen_Burn t1_jb3jo8m wrote

Carbon fiber always gets people.

Got called in to consult with a development team that was having paint issues. Their brilliant plan which they had spent the last six months perfecting was changing out glass fibers for carbon fibers in an injection molding system. Which is fine and dandy except they also:

Vibromelted brass inserts into the plastic in order to secure the lid to the body with cadmium coated steel bolts and then sprayed the entire interior with an EMI coating witch was 92%wt silver.

It was hilariously bad. The piece was supposed to pass 168 hours salt fog with no visible signs of rust. The first check was 18 hours into the run and not only was there corrosion products running off the side, it was red rust from the steel.

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rogerarcher t1_jbrmmbo wrote

How did they fix it?

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Bunsen_Burn t1_jbt0esn wrote

The program was supposed to be a drop in replacement upgrade. When they realized they would need to start making serious changes to fasteners and other equipment they just killed the entire thing. The changes they would of had to make were far outside the scope of their original intent and they were basically out of project money.

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The_mingthing t1_jb2jsrm wrote

Could you measure voltage difference to get a guideline?

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ferrouswolf2 t1_jb2ue0g wrote

That’s going to depend on the concentration of the corrosive electrolytes, and even then a small voltage can still result in serious corrosion over time.

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Flaxatron t1_jb2zwja wrote

You can measure the voltage. It's tougher to predict the damage or the location of the damage. All you'd really be able to decern is roughly how many atoms are moving around

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iammandalore t1_jb2qyrt wrote

I don't want to create a separate question so I'm hoping you can answer. If you make an alloy out of two metals far apart on the chart, say titanium and zinc, is there internal electrical activity or corrosion within the alloy?

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ferrouswolf2 t1_jb2ui8g wrote

Depends on the structure, and their solubility. Do you have a true alloy or just a mix of pockets of one material inside the other?

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Outrageous-Rise1336 t1_jc0zv5i wrote

Note that galvanic corrosion occurs only when the dissimilar materials are in contact with an electrolyte.

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