How to avoid galvanic corrosion

Xiter

Xiter

Member
I’m going to install auxiliary lamps for the main beam. These require support struts that I intend to attach to the aluminium beam directly below the hood. What screws can you recommend that won’t cause galvanic corrosion to the aluminium beam?
I intend to use the holes used to fasten the bumber below the hood. Plastic rivets hold the bumber to the beam. If the hood is removed from the vehicle the rivets are visible.
 
I've attached a pdf on this subject from the swedish corrosion institute. A stainless steel screw (SS2343) was screwed into an aluminium plate which were exposed to a salt solution for 96 hours.

The two top pictures show what happened to the aluminium and there are corrosion residue from the aluminium on the screw as well. The left lower picture shows how a protective gel called Tef-Gel protected the aluminium from corrosion.
 
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You could cut a square hole onto the aluminium, coat the exposed edges and then use a suitable captive nut, available from Audi. These are steel or brass nuts encapsulated in a rubber/plastic housing that you insert into the hole (square to stop rotation on tightening).

Cheers,

Mike
 
what are you going to use? Big Knicks?

did you try talking to QPax for a lightbar? I had my comets attached to the bonnet, with the second connection from the top of the grill section, though I think I'll be redoing it so that they are integrated into the grill itself. That was suboptimal, but not bad; pretty functional, too. Minimal vibration.

Bret
 
If you're worried about corrosion, you can try to find some epoxy. There are extremely strong epoxy that bonds metal or just about everything, they are also used in aviation for metal bonding.

The only downside is, you can't remove it once it is cured, it is stupidly strong and no heat gun can soften it. And you have to leave it in a dry place to cured for at least 24hr (the warmer the better).
 
bretti_kivi said:
what are you going to use? Big Knicks?

did you try talking to QPax for a lightbar? I had my comets attached to the bonnet, with the second connection from the top of the grill section, though I think I'll be redoing it so that they are integrated into the grill itself. That was suboptimal, but not bad; pretty functional, too. Minimal vibration.

Bret
Click to expand...

Yes, four Bosch Rallye 225, also called Big Knicks as you say. Pic attached. Support struts go from the top of the Knicks to something solid. They are not visible on the pic.
I already have my own bar. Just need to find a good location to fasten the support struts on top of the Knicks, and now the aluminium beam under the hood will be very solid indeed for this purpose. I think I will try to get hold of aluminium screws.
 
humps said:
If you're worried about corrosion, you can try to find some epoxy. There are extremely strong epoxy that bonds metal or just about everything, they are also used in aviation for metal bonding.

The only downside is, you can't remove it once it is cured, it is stupidly strong and no heat gun can soften it. And you have to leave it in a dry place to cured for at least 24hr (the warmer the better).
Click to expand...

Not a bad idea to use epoxy, but I would prefer a less permanent solution.
 
why not try and get some of the screws normally used to hold the speakers in place? They're M5.....

4 big knicks? Oha. This I'd love to see, they'd freak here :D

For those of you who never get to use High beam... it's not very good. These should be from another planet, expected range around 600m, no? and four of them....

Bret
 
bretti_kivi said:
why not try and get some of the screws normally used to hold the speakers in place? They're M5.....

4 big knicks? Oha. This I'd love to see, they'd freak here :D

For those of you who never get to use High beam... it's not very good. These should be from another planet, expected range around 600m, no? and four of them....

Bret
Click to expand...

Expected range should be...enough:)

Living in darkness for 6 months of the year...yes, you know what I'm talking about. I actually am almost finnish since my mom, both grandmas and my grandpa from my mother's side is finnish.

After further investigation, I've found numerous bits and pieces behind the hood I might be able to use for the struts. So hopefully, the aluminium beam will be left alone, but we'll see. The only issue is hood clearance but I'll sort it out when I get there. Thanks for tip about the speaker screws, are they aluminium? Oh, and today I've had the first taste of road salt this winter :mad:
 
I don't think they're alu, but they're coated and they're screwed into the alu square nuts on the back of the "aggregatenträger" (inner skin) of the door.

Hood clearance is minimal, you have 2-3mm to play with *max* depending. The chrome on the bottom of the grill is over plastic if memory serves, but you might want to create some "channels" to ease things along. the grill is a €20 replacement, a bumper €1000.

Yes, darkness.... I'm just hunting and appear to have found a very good deal in the UK on Comet 200 Xenons. They're for her... this is why I was looking at a bi-xenon upgrade. Now I understand more about epoxy resin, I might actually get on with it, too ;)

Bret
 
I've decided not to use the plastic unscrewing snap rivets. Instead I will probably use aluminium pop nut blind rivets with M5 aluminium screws.
The pop nut blind rivets will fit the holes in the beam just right and will provide me with enough clearance for the bonnet to close (I hope):)

http://www.emhart.com/products/pop/popnut.asp
 
Update

Pics of toady's progress. The popnuts are there and the support struts as well. This is a very solid installation. I'm happy with the result. Tomorrow it's time for the electrical bits. Still waiting for the aluminium M5x20 screws though. When I get them I change the temporary steel screws I use for testing purposes only. Hood clearance with the thick steel screws is none.
 
Do you have to make a bracket for your front number plate (not sure of the laws on this for you). The A2 rally car now you could have got an old bonnet and done a bonnet pod like the old rally cars

Cheers Phil
 
The installation is complete and now I have finally seen the light :)

Fastening holes for the front number plate is integrated in the bar that holds the lights. You can actually see the number plate on the two previously posted pics below the lights.

Where the number plate used to be, there is an old numberplate turned over with it's backside forward as a cover for the brackets holding the light bar.
 
Update.

Steel screws replaced with aluminium screws (black flat head screw) to prevent galvanic corrosion. A late update though since it was done about a year ago :)
 
Another pic of the two (out of three) brackets that hold the light bar.
There are reinforcement plates on the back side as well.
 
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