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Discussion Starter · #1 ·
Wikipedia:
"Galvanism is a term invented by the late 18th-century physicist and chemist Alessandro Volta to refer to the generation of electrical current by chemical action." He named it for Luigi Galvani who "thought his discovery to be a confirmation of the existence of 'animal electricity,' a vital force which gave life to organic matter."

Be that as it may, I found this presentation of The Galvanic Table.

Consider this curious statement however:
"When any two metals in the 'Galvanic Table' are in contact, with an electrolytic [e.g., road-salt spray] present, the one with the lower number is corroded. The galvanic action increases as the metals are farther apart in the Galvanic Series. It is not always true that there is greater corrosion the further down the scale one goes. In certain cases one metal immediately following another may be very corrosive."

I interpret this to mean, "Zinc and aluminium can be expected to have relatively low galvanic action because they are near each other in the Galvanic table, UNLESS their proximity is very corrosive although they are near each other in the table."

Is there a Practical reference guide to mixing and matching metals with the Insight's aluminium?
Something along the lines of "aluminium/zinc RELATIVELY INERT", "aluminium/copper CORRODES ALUM"?

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Discussion Starter · #2 ·
More on the subject from Fastenal.com is attached.

I find it counter-intuitive that "just any stainless steel fastener is NOT preferable to zinc or galvanized for use with aluminium (if I'm interpreting it right). However that's how I'm interpreting it, and I'm off to the local hardware to propriate a couple of zinc-plated "jack nuts" to try out.

The second page of the document has this handy compatibility chart I had dreamed of (but NOTE "Martensitic SS, Type 410" is "NEVER RECOMMENDED" for use with aluminium, but how many would have guessed that steel, or galvanized, or iron, or zinc would be preferable?):
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I keep hearing about galvanic corrosion, but all of my worst fastener experiences have been with steel on steel! Except for the front left bolt on my driver's seat!
 

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Discussion Starter · #5 · (Edited)
Nothing to add, but I posted a thread some years ago that was similar: Galvanic corrosion, Insight sticks, busbars, and fasteners
Thanks @eq1. I had searched on electrolysis but was overwhelmed with warnings about it. When I found "galvanic" by association through the web it didn't occur to me to search IC again--I'd never run across it here before.

To me the "Plating Compatibilty Chart" says use zinc- or galvanized-plated fasteners in aluminium.

@Gasoline Fumes One of the articles I saw addressed itself to "designers" and mentioned multiple types of corrosion they had to account for: chemical (in which galvanic is classed by some), and oxidation were present of course, but I seem to recall stress and pitting and crevice as others.
 

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...To me the "Plating Compatibilty Chart" says use zinc- or galvanized-plated fasteners in aluminium.
Yeah, that's what it looks like to me. But I find it odd that the table shows a "1-1" relationship when the "base" metal is aluminum and the "fastener" is zinc -- but it shows a "1-2" relationship when the base metal is zinc and the fastener is aluminum. That makes no sense to me, why would there be a difference? Maybe it has to do with plating vs. solid metal?

In any event, when I was looking into this sort of thing back in the day, I realized it was more complex and difficult to figure out in the real-world than I had realized initially. For example, in that thread I posted a link to, I mention that I thought the battery sticks have stainless steel lugs/ends - they totally look like that.* But later I started to wonder whether they are something else. Same thing goes for other things: It's hard to know/figure out exactly what metals you're dealing with... The battery sticks (OEM) might have nickel-plated lugs, not stainless steel. What I thought were aluminum busbars on the battery pack I think are actually zinc or 'Dacro' coated copper (a lot of the Insight fasteners are this 'Dacro' thing, it looks like some kind of zinc-coating or plating)...

Funny, just over the last number of days I've been removing old knob and tube wiring in my house. The old wire is interesting - if I pull the rubber-whatever cladding off of the actual wire, the wire is a nice, clean shiny silver color, not copper. I think it must be tin-plated copper, you can see the copper in the center of the wire, when cut.

Also in that thread I posted it's apparent that troubles crop-up when trying to know what alloy you're dealing with - lots of different aluminum alloys, for example.

*edit: fyi, here's an old image I have of the stick lugs, for earlier after market sticks. vs. OEM. Hmm, don't know what they are, but they're 'ferrous', they're magnetic (I have one sitting on my desk that I just tested with a magnet. On the other hand, I can see a reddish tinge on the threads inside, where some plating must have worn-off, looks like copper):
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I keep hearing about galvanic corrosion, but all of my worst fastener experiences have been with steel on steel! Except for the front left bolt on my driver's seat!
Iron (all metals really) corrodes regardless. Also a matter of 99% of the fasteners we encounter being steel on steel or iron. When the engineers do their homework, you won't have galvanic corrosion problems. I've found a few cars with the wrong AL alloy for conditions or with improper replacement bolts that a part all but disintegrated on contact due to it.
 

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Discussion Starter · #8 ·
@eq1 Somewhere in my readings I did see that there was different behavior for metal1 base and metal2 fastener and v.v., but I did not understand the explanation.

As I assume you did, I thought since the contact area was the same in both cases the behavior would be as well. Now I think about it however, it's probably more important to think of the base metal as an "ocean" of atoms in which the fastener is suspended.

Coupled with the information that the "anodic" component of a dissimilar pair will sacrifice itself for the "cathodic" one, it's easier to imagine different behaviors when swapping the two metals around. An anodic "ocean" would have more to donate to a cathode than would a fastener.
 

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I keep hearing about galvanic corrosion, but all of my worst fastener experiences have been with steel on steel! Except for the front left bolt on my driver's seat!
I can only assume you've never worked in the marine/boating repair industry, which makes me think you've probably never heard of an "OMC heat wrench" either...LOL (nickname for an Oxy/Acetylene torch used to remove corroded fasteners from aluminum with a bit of heat)

@ eq1 - BennyMaxwell's attachment may help to explain the difference between a fastener and it's base metal, and why it might have a different rating when the fastener role is reversed (last couple of paragraphs).

P.S. - I vote for zinc plated steel fasteners for my aluminum Insight.
 
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