Motor Vehicle Maintenance & Repair Asked by user2864293 on April 26, 2021
Looking for some chemistry expertise/experience here. I bought some ARP head studs, which didn’t quite fit. I don’t have a thread micrometer, so I can’t say exactly how oversized they were, but I wasn’t going to get them in without a breaker bar (even then it’s a maybe).
So I took a little off with a die and then installed the studs with a little oil. The block is aluminum. My concern is that now I may have a risk of corrosion between the aluminum block and the studs, which have exposed steel since the machining with the die removed the oxidation coating.
My guess is that I should be ok since oil is not very conductive, but I’m not very confident in that guess.
My understanding is that anytime you have dissimilar metals bridged by an electrolyte, that’s a battery and the metals will corrode. What about when the dissimilar metals are in direct contact? I oiled the threads, but I’m sure there’s some fraction of surface area that’s not covered by oil. Is that at a risk to corrode?
So in summary, I have two questions
1) Do I have a corrosion risk between aluminum and steel, when bridged by oil?
2) Do I have a corrosion risk between aluminum and steel, when in direct contact?
Electrolysis happens with the passage of electric current.
Steel will corrode in aluminium - removing the protective coating was not a good idea.
Where did you get these new studs? - studs supplied from the manufacturer ie “original” parts rarely have this oversize problem.
If these “new” studs came from a nut & bolt supplier then not only the size may be incorrect, but the grade as well.
I would suggest you source the correct replacement studs from a dealer.
Answered by Solar Mike on April 26, 2021
A black oxide or "bluing" coating on steel provides little corrosion protection so very little has changed corrosionwise. Parkerizing/phosphate gives a little protection but not enough to make a difference here. And ,as the studs are installed , likely some of the original surface is broken. These surfaces are likely applied to help hold lubricant on the fasteners to reduce the risk of galling of the aluminum. ( Not for corrosion protection).
Answered by blacksmith37 on April 26, 2021
The automobile manufacturers use stainless fasteners in aluminum heads routinely.
You don't have too much worry.
You can use stainless and aluminum together but expect you will have corrosion eventually and prepare for it. But your aluminum or steel will not rust away.
Of course you cannot weld these metals together.
Read around the web, this is well trodden ground.
https://www.practicalmachinist.com/vb/general-archive/will-s-s-bolts-work-aluminum-88508/
https://www.bassresource.com/bass-fishing-forums/topic/20093-what-screws-bolts-for-aluminum-boats/
Answered by geoO on April 26, 2021
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