will grounding prevent aluminum corrosion?

[macPT]

Hi all

1 - I have an aluminum frame;
2 - This aluminum frame is supported by a galvanized steel structure;
3 - Both the aluminum frame and steel structure are grounded, by means of separate conductors, connected to the same ground collector.

Will this prevent galvanic corrosion? (the metals should have the same potencial!)

Thanks

MAC

 

[IRstuff]

I don't think so. The potentials in question are electrochemical, not electrical.

TTFN
faq731-376

 

[Compositepro]

Connecting the metals so a current can flow from one to the other is what causes corrosion. the solution is to electrically isolate the two.

 

[mfgenggear]

I read that when aluminum is machined the oxide surface that helps with corrosion is removed.
so that applying chem film, anodize or paint helps with corrosion by replacing the oxide surface.
alos heat treating depending on the type aluminum.
any time dissimilar metals are assembled together there can be issues.

to get an actual sientific answer it can be easily googled.

HTH

Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[TomDOT]

What environment is the structure in? The potential difference is only .30-.35V - that's not a lot for galvanic corrosion. Unless you are in a particularly wet or particularly salty environment (rain forest, coastal, offshore, et cetera) the galvanic corrosion should typically not be an issue.

 

[stanweld]

mfgengear,
After machining, the protective oxide film is rapidly regenerated. It is true, that anodizing and other surface treatments can improve corrosion resistance.

macPT,
Grounding as stated will not prevent galvanic corrosion. But as TomDOT states, the galvanic potential mismatch is minimal until the zinc coating is removed from the steel.

 

[macPT]

Hi
Thanks for the input. The Alu frame is anodized, but the environment is wet.
I am not expecting corrosion to be a big issue, but I was expecting that grounding would improve corrosion resistance...

 

[MPEngineer]

Unfortunately quite the opposite. If you apply an epoxy coating with a primer, such as one from Akzo-Nobels' 10-P4-3, or 466-23 Series topcoat that would probably do it. You can also use PR1776 sealant from PPG aerospace between the two parts to mitigate the corrosion.

 

[MPEngineer]

You can also look at MIL-STD-889 and it will cover this topic in depth and also give you some methods to mitigate corrosion.

 

[Burdy]

Isolate the Aluminium from the Galv structure with PTFE pads to eliminate any electrical difference at the joints (where the material will corrode) then connect your earthing strap (because you could end up with static) through a sacrificial anode i,e, lead.

 

[coolbreeze]

Some Al alloys will oxidize much faster than others. 2XXX series Al is used extensively in corrosion environments, aircraft wheel wells for example. You may want to consider other forms of corrosion. If the Al frame is under load, SCC may also be a problem.

 

[Metalhead97]

macPT,

In just H2O, the Al2O3 coating is pretty stable. Halogens in solution will destabilize the oxide film and initiate corrosion. Grounding the Al plate, would place the plate at the potential of the surroundings and that would only facilitate charge flow and not hinder it. Get a car battery and connect the negative terminal to the Al Plate and 'ground' the positive terminal. That would put the plate at a higher (more negative) electrical potential than ground. That may be be enough to protect the plate. You could also use a sacrificial anode.

MH

http://www.linkedin.com/pub/luke-autry/1b/510/566