Fasteners to prevent galvanic corrosion?

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Joachim

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Hi, I see some vendors that offer fastener kits to our cars are supplying all stainless A4. With our cars being a mix of aluminum, steel, galvanized steel and potmetal, I can't help but think that this is a really bad idea due to the galvanic corrosion that would occur... It must be false security using pretty stainless bolts, thinking that because they don't rust that it will keep the car looking beautiful and that the bolts would release easier in the future, right?

With stainless being the most noble metal of those I have mentioned above, this type of fastener would act as a cathode, accelerating the corrosive attack on whatever it is attached to... which in our cars would usually be far more cumbersome and expensive to mend or replace than a simple fastener. And, with the hardness of a stainless bolt, if the corrosion between the two metals causes it to seise up, and it either snaps or needs drilling out, it will be much more difficult than if the bolt was softer.

Ideally the metal of the fastener should be the same as whatever it is bolted to. If this is not possible due to one having to bolt different metals together, like aluminum to steel, then the bolt should be the equivalent of the more noble of the two. And, if this is not possible, then the fastener should be the most noble in the mix, but as close as possible in its electrode potential.

To what extent this is simply a theoretical problem with me being paranoid or an actul and significant problem we need to be aware of I don't know... I'm a noob when it comes to Land Rovers. In boats however, this is a significant issue as it is bobbing in an electrolyte called sea water and often is connected to land power that can spur galvanic corrosion even further... I assume that LR used positive earth for amreason.

I would really like to hear what you use where, why you use it, what your mileage is, what you would not use and why. In addition to fasteners, do you use electrical inulators such as pastes, if so which? Pastes and greases may keep out water and other electrolytes, they can seal the two metals from eacother, and they can act as a release agent. But sometimes you want thread lock agents... Nylon rings can provide insulation where steel touches aluminum, as can different type of caulking. What do you and do you not use, and why?

I am conscidering using mainly 8.8 hot galvanized bolts combined with copper grease and spring washers (nuts with nylon locking get brittle and are not really reusuable). I am also conscidering using nylon rings in some places to attach the aluminum body to the steel. As for choice of pop rivets, I have no idea... In boats we use monel, but they aremvery pricey. As for caulking or other form of insulators, I have no idea.

Please contribute.
 
Muchacho interested as I'm an electrical engineer with an interest in electrolytic corrosion, but zero actual experience of proper practice on Landies. Real world experience will be everything here. :cool:
 
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look at duralec or tefgel or paint can work. you need to isolate or keep em dry.

galved bolts will still go, the zinc sacrifices itself first so takes longer.
 
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I've been wondering the same myself as I bolt together my project with a mixture of original bolts where they are sound or new stainless from a kit where they are rusted or safety critical. There was another question the other day about this and I found this page:
Article: Bimetallic (galvanic) corrosion risks from contact with galvanised steel or aluminium

They specifically say that ally rivets in stainless is a bad idea but stainless fasteners in large pieces of ally should be ok and that stainless + galv should be ok.

I too would be interested to hear from anyone who knows about this stuff in practice...
 
To be fair, with stainless steel this all takes so long that your chassis will have turned to dust before you need to worry about it. It's far too easy to start thinking to much about what actually needs to be done. Keep it simple...

I fitted stainless steel bolts where ever I could to mine years and years ago, those bolts are the ones that undo easily when replacing a part, the plain steel or BZP steel bolts are the ones that have rusted in and seized, and that's with copper slip....

I'd not give it a second thought and fit stainless every time.
 
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Thanks Murtle, this is what I wanted, not just theory but experience.

Murtle, what type of rivets do you use? And, do you use stainless on both galvanized steel and aluminium? On a boat, when you use a stainless shackle on a galvanized anchor chain you can bet on having to cut a few links off that chain every odd year, it disintegrates really fast... but then again, that is on a boat where the conditions for galvanic corrosion is extreme.

Also, do you use copper paste on the bolts? Thread lock fluid?

Lastly, between the aluminum panels and steel, do you use any kind of insulator... caulking, electrical tape, rubber, plastidip???
 
I've just repaired the bonnet on series 3, that's a steel frame fixed to an aluminium skin with solid aluminium rivets. Only protection on the rivets is the anodise. The frame had rotted away (and not where it's in contact with the aluminium skin) there was never a layer of paint between the too. That's got to be over 35 years on contact between the two metals with very little galvanic corrosion evident (small amount of white powder just under the joint)

For other rivets I use sealed blind rivets with stainless steel pins, the only reason for the stainless steel is so it doesn't leave rust streaks down the paint in years to come.

For bolts and machine screws I always use copper slip and spring washers, and as standard engineering practice put a plain s-steel washer between the spring washer and the mating surface.

For body mountings to chassis I used a thin rubber gasket less than a couple mm thick. No idea the grade or type however.
 
Joachim said:
Hi, I see some vendors that offer fastener kits to our cars are supplying all stainless A4. With our cars being a mix of aluminum, steel, galvanized steel and potmetal, I can't help but think that this is a really bad idea due to the galvanic corrosion that would occur... It must be false security using pretty stainless bolts, thinking that because they don't rust that it will keep the car looking beautiful and that the bolts would release easier in the future, right?

With stainless being the most noble metal of those I have mentioned above, this type of fastener would act as a cathode, accelerating the corrosive attack on whatever it is attached to... which in our cars would usually be far more cumbersome and expensive to mend or replace than a simple fastener. And, with the hardness of a stainless bolt, if the corrosion between the two metals causes it to seise up, and it either snaps or needs drilling out, it will be much more difficult than if the bolt was softer.

Ideally the metal of the fastener should be the same as whatever it is bolted to. If this is not possible due to one having to bolt different metals together, like aluminum to steel, then the bolt should be the equivalent of the more noble of the two. And, if this is not possible, then the fastener should be the most noble in the mix, but as close as possible in its electrode potential.

To what extent this is simply a theoretical problem with me being paranoid or an actul and significant problem we need to be aware of I don't know... I'm a noob when it comes to Land Rovers. In boats however, this is a significant issue as it is bobbing in an electrolyte called sea water and often is connected to land power that can spur galvanic corrosion even further... I assume that LR used positive earth for amreason.

I would really like to hear what you use where, why you use it, what your mileage is, what you would not use and why. In addition to fasteners, do you use electrical inulators such as pastes, if so which? Pastes and greases may keep out water and other electrolytes, they can seal the two metals from eacother, and they can act as a release agent. But sometimes you want thread lock agents... Nylon rings can provide insulation where steel touches aluminum, as can different type of caulking. What do you and do you not use, and why?

I am conscidering using mainly 8.8 hot galvanized bolts combined with copper grease and spring washers (nuts with nylon locking get brittle and are not really reusuable). I am also conscidering using nylon rings in some places to attach the aluminum body to the steel. As for choice of pop rivets, I have no idea... In boats we use monel, but they aremvery pricey. As for caulking or other form of insulators, I have no idea.

Please contribute.
Click to expand...

do a search of what copper(copper grease) does to aluminium
 
Murtle said:
I've just repaired the bonnet on series 3, that's a steel frame fixed to an aluminium skin with solid aluminium rivets. Only protection on the rivets is the anodise. The frame had rotted away (and not where it's in contact with the aluminium skin) there was never a layer of paint between the too. That's got to be over 35 years on contact between the two metals with very little galvanic corrosion evident (small amount of white powder just under the joint)


For body mountings to chassis I used a thin rubber gasket less than a couple mm thick. No idea the grade or type however.
Click to expand...

Probably because it is quite warm and dry under the bonnet, and the problem is worse where the metals are almost always wet, like some of the body mounts. :) Electricity likes water.

I always try and make little gaskets wherever there is metal to metal contact. Helpful with galvanic issues where the metals are different, stops them rusting together if they are the same. I don't use anything purpose made, just old plastic, side of a placcy oil tin is quite good.
 
Thor1950 said:
do a search of what copper(copper grease) does to aluminium
Click to expand...

Probably help increase conductivity and galvanic issues, if anything. A smear on bolt threads is all I would use it for.:)

Joachim, just have a check that the original bolts are only 8.8 steel. They might be meant to be a stronger bolt, not sure.
 
dominicbeesley said:
I've been wondering the same myself as I bolt together my project with a mixture of original bolts where they are sound or new stainless from a kit where they are rusted or safety critical.
Click to expand...

stainless isn't as strong as steel. the chromium weakens it. so don't change structural 8.8+ with stainless.

Murtle said:
To be fair, with stainless steel this all takes so long that your chassis will have turned to dust before you need to worry about it. It's far too easy to start thinking to much about what actually needs to be done. Keep it simple...

I fitted stainless steel bolts where ever I could to mine years and years ago, those bolts are the ones that undo easily when replacing a part, the plain steel or BZP steel bolts are the ones that have rusted in and seized, and that's with copper slip....

I'd not give it a second thought and fit stainless every time.
Click to expand...

depends on what you are fastening it to. we are mainly talking about into aluminium. steel to steel is a different matter.

stainless on aluminium is bad. the alu will go quick.

zinc is less noble than alu, so the zinc coated bolts should strip the zin first, start to rust and then kill the aluminium as steel is more noble than alu. but steel is closer to alu than stainless on the noble scale.

Murtle said:
I've just repaired the bonnet on series 3, that's a steel frame fixed to an aluminium skin with solid aluminium rivets. Only protection on the rivets is the anodise. The frame had rotted away (and not where it's in contact with the aluminium skin) there was never a layer of paint between the too. That's got to be over 35 years on contact between the two metals with very little galvanic corrosion evident (small amount of white powder just under the joint)

For other rivets I use sealed blind rivets with stainless steel pins, the only reason for the stainless steel is so it doesn't leave rust streaks down the paint in years to come.

For bolts and machine screws I always use copper slip and spring washers, and as standard engineering practice put a plain s-steel washer between the spring washer and the mating surface.

For body mountings to chassis I used a thin rubber gasket less than a couple mm thick. No idea the grade or type however.
Click to expand...

you need an electrolyte and series are birmabright iirc
 
trax said:
stainless isn't as strong as steel. the chromium weakens it. so don't change structural 8.8+ with stainless.



depends on what you are fastening it to. we are mainly talking about into aluminium. steel to steel is a different matter.

stainless on aluminium is bad. the alu will go quick.

zinc is less noble than alu, so the zinc coated bolts should strip the zin first, start to rust and then kill the aluminium as steel is more noble than alu. but steel is closer to alu than stainless on the noble scale.



you need an electrolyte and series are birmabright iirc
Click to expand...

I'll just carry on doing what I know works without issue, and that's using stainless steel fasteners and copper slip. It's not for Marine, its for land use, which is an order of magnitude different.

Trax, please define your statement "stainless isn't as strong as steel" where do you get this information from? What grade of Steel, and What grade of Stainless? You do realise that 8.8 as a grade of steel fastener is minimum 800 N/mm^2 or MPa , and an A2-80 Stainless steel fastener is the same 800MPa.

I also assume your saying that birmabright is not aluminium?


Seriously this is a Land Rover which at best is a basic mechano set not rocket science. It doesn't need to be over complicated, just fix and enjoy it. It's nice and sunny here so I'm off out side now to do exactly that. :)
 
Turboman said:
Probably help increase conductivity and galvanic issues, if anything. A smear on bolt threads is all I would use it for.:)

Joachim, just have a check that the original bolts are only 8.8 steel. They might be meant to be a stronger bolt, not sure.
Click to expand...


If this is a series Land rover using imperial fasteners then you will not see an 8.8, or any other numeric designation, they should only have a series of lines on the head. Either nothing, 3 lines 6 lines, possibly 9 but I doubt it.
 
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I thought A4 80 stainless offerred approximately the same strength as 8.8 steel... Pretty much exact in fact Check this overview of fastener tencile strength There are many different qualities of a4 stainless. I believe that this is a misconception from people having used low grade stainless bolts.

I also have a paralell discussion going on in a Norwegian forum. There it seems to be close to a consensus that there is an issue with stainless fasteners on aluminium but that this issue is of no real consequence on our cars. The reasoning behind this is that the surface area and size of the aluminium parts versus the stainless fasteneres is so much greater, making the galvanic issue miniscule. It seems as though stainless is the most commonly used here, and some report that ten years later the bolts still come loose easier, and with no rust, compared to their 8.8 alternative. I have read other articles on the web that supports this reasoning... Still, I doubt I would use anything but original on parts where exact stretch and torque settings is absolutely essential, like engine heads, etc.

If this reasoning holds true I would be far more concerned using aluminium pop rivets that would touch steel than the other way arround.

Has anyone here experienced any problems using stainless A4 (i presuppose 80 hardness and not 50)? The more I read the more I'm being pulled towards using stainless A4-80 as my preferred fastener.

As for insulating larger metals from eachother I don't know. Would it even matter if there is a fastener in place that can act as a conductor? Wouldn't you have to use plastic fasteners then?
 
Murtle said:
I'll just carry on doing what I know works without issue, and that's using stainless steel fasteners and copper slip. It's not for Marine, its for land use, which is an order of magnitude different.

Trax, please define your statement "stainless isn't as strong as steel" where do you get this information from? What grade of Steel, and What grade of Stainless? You do realise that 8.8 as a grade of steel fastener is minimum 800 N/mm^2 or MPa , and an A2-80 Stainless steel fastener is the same 800MPa.

I also assume your saying that birmabright is not aluminium?


Seriously this is a Land Rover which at best is a basic mechano set not rocket science. It doesn't need to be over complicated, just fix and enjoy it. It's nice and sunny here so I'm off out side now to do exactly that. :)
Click to expand...

i'm not going into chemical analysis or debating the science of bolts. For our landy related applications i'm making him aware that you can't go replacing stainless for structural bolts willy nilly. Apart from strength, stainless has a tendency to snap when stressed; steel will bend.

Also looking for an 8.8 stamp is a lot easier than not getting confused with a2-70 and a2-80 or a4s.

birmabright is an alloy of alu and magnesium iirc. google will give more info

thanks for the sunshine wisdom
 
Joachim said:
I also have a paralell discussion going on in a Norwegian forum. There it seems to be close to a consensus that there is an issue with stainless fasteners on aluminium but that this issue is of no real consequence on our cars. The reasoning behind this is that the surface area and size of the aluminium parts versus the stainless fasteneres is so much greater, making the galvanic issue miniscule. It seems as though stainless is the most commonly used here, and some report that ten years later the bolts still come loose easier, and with no rust, compared to their 8.8 alternative. I have read other articles on the web that supports this reasoning... Still, I doubt I would use anything but original on parts where exact stretch and torque settings is absolutely essential, like engine heads, etc.
Click to expand...

i doubt you'd be threading into alu, so bolts being loose is a non issue for galvanic corrosion imo.

it's when the heads or shanks are in contact with alu and it starts to oxidise and corrode. this doesn't take ten years.

real life example is the two bigass holes on the back of my roof where the PO had mounted two work lamps. the area has completely corroded away leaving a 2 inch gap which i had to fill.

i'm assuming vibration between the galv mounts and the body caused direct contact between the metals and rain started the process. the mount was rusty probably due to the zinc sacrificing itself exposing steel, then it started to oxidise the alu.

seatboxes are also known to oxidise badly in the corners
 
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trax said:
stainless has a tendency to snap when stressed; steel will bend.
Click to expand...

Again where are you getting this data, please state grades of steel and stainless for your examples. Look at the yeald of them both. If anything stainless steel is more likely to bend instead of snap than steel.

trax said:
Also looking for an 8.8 stamp is a lot easier than not getting confused with a2-70 and a2-80 or a4s.
Click to expand...

It's just the same idea, look on the head, not complicated at all. In reality your only looking for the 50, 70, 80, or 100 with stainless to have a good indication of N/mm^2.
 
8.8 and 4A-80 stainless has the same tencile strength, meaning that they shear/snap at the same torque...

Hardening stainless steel is more difficult than carbon steel, hence much stainless sold is often soft. But, you do get hard stainless. Buy the right stuff!
 
Murtle said:
If this is a series Land rover using imperial fasteners then you will not see an 8.8, or any other numeric designation, they should only have a series of lines on the head. Either nothing, 3 lines 6 lines, possibly 9 but I doubt it.
Click to expand...

Fair enough, forgot it was a series, my 90 is metric. I only suggested he check the strengths to be sure.

Joachim said:
I thought A4 80 stainless offerred approximately the same strength as 8.8 steel... Pretty much exact in fact Check this overview of fastener tencile strength There are many different qualities of a4 stainless. I believe that this is a misconception from people having used low grade stainless bolts.

I also have a paralell discussion going on in a Norwegian forum. There it seems to be close to a consensus that there is an issue with stainless fasteners on aluminium but that this issue is of no real consequence on our cars. The reasoning behind this is that the surface area and size of the aluminium parts versus the stainless fasteneres is so much greater, making the galvanic issue miniscule. It seems as though stainless is the most commonly used here, and some report that ten years later the bolts still come loose easier, and with no rust, compared to their 8.8 alternative. I have read other articles on the web that supports this reasoning... Still, I doubt I would use anything but original on parts where exact stretch and torque settings is absolutely essential, like engine heads, etc.

If this reasoning holds true I would be far more concerned using aluminium pop rivets that would touch steel than the other way arround.

Has anyone here experienced any problems using stainless A4 (i presuppose 80 hardness and not 50)? The more I read the more I'm being pulled towards using stainless A4-80 as my preferred fastener.
Click to expand...

tbh I wouldn't get too obsessive about it, in a way the original idea was to make things fairly cheap so you could just replace them if needed during maintenance or component replacement.[/quote]


[/quote]As for insulating larger metals from eachother I don't know. Would it even matter if there is a fastener in place that can act as a conductor? Wouldn't you have to use plastic fasteners then?[/quote]

If you don't like it, just don't do it, Simples! Just saying what has worked for me on a number of working landrovers over the last thirty years.
It is quite good for reducing noise as well. :)
 
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