Outer Limits 4x4 Board

being that there's a fair mix of alloy and steel through the old rangies.

other than paint what stops the 2 different metals eating each other away?

the reason I'm asking is for my extracab we re-inforced the back of the cab and actually used 50x50RHS as the C-pillar, using steel in an alloy body was the only thing my engineer queeryed over the phone before his visit next week. what can you give me to arm myself with?

Cheers

Simon

Keep the moisture out and it should be ok. For inside the cab there are several wax substances out on the market, waxol springs to mind. fish oil is good if you can live with the smell. Body deadener tar stuff would be good on the joins underneath.

Normally on a rover when they are assemble the steel to ally joins, ie. a door skin to a door frame they use a bit of drip check too. It also stops squeeks.

Andrew

The inner shell is steel the external panels are alloy bar the the rear tailight panels and the bonnet on early models. If you are talking the back of the cab section it would be steel on steel.

Corrosion is a galvanic action, like an electrolytic cell (battery). The cell consists of 3 parts: anode, cathode and electrolyte. Eliminate one of these or prevent electrical contact (insulation) between them and you don't have a cell.

Electrons travel through the electrolyte between the anode and cathode. The anode corrodes as result of lossing electrons. And the cathode is built up. In welding, the electrode is the anode and the work is cathode, air is the electrolyte, but that is getting too far of topic.

Aluminium is much more anodic than steel so a higher voltage is present in the cell.

Salt water is a better electrolyte than pure water. Which is why fourbys used on the beach rust out quicker.

The inhibitor/anti freeze in engine cooling systems reduces the effectiveness of the coolant as an electrolyte, to reduce corrosion of aluminium components with cast iron blocks.

When steel is rolled (or otherwise worked), changes in the structure make some parts of the surface more anodic than other parts. That is why you will see some parts pitted and build up on.

With a cavity or gap, there is less oxygen inside the cavity and this makes for a larger electo potential (voltage difference) resulting in corrosion. This is why it is best to seal weld all around a joint even if that much weld is not required for strength.

So, prevent electrical contact between the surfaces and fasteners, or prevent moisture (electrolyte) from getting near the joint.

Years ago when I was involved with yatchs, zinc chromate was by far the best thing to use between fittings and aluminium mast (etc). But this is a banned substance now.

Main frame of a Rangie is steel, it's only the skins that are alloy, so you would be wrong in using alloy.
Can't say I had any issues of corrosion between joints on my old 76 model, rust was from normal, water buildup/bare metal issues on the steel part only.

Besides taking precautions to reduce corrosion, remember that the aluminium is more anodic than the steel, so it will corrode 1st, but it is not structural.

Your C pillar being structural steel should be affected as much and no worse than if it had steel body skin.

cheer's bushy65, exactly what i was after, I know the basics of this stuff but not to that extent!
the intial engineer we dealt with who said it would be ok is no longer qualified. and the new one didnt sound real keen on the phone

and we did seal all welds, and then any where alloy contacts steel we made sure both surfaces were fully painted and sealed, wednesday is the day of truth

Simon

Regardless of all the above, where you have enclosed the back of the cab it will be ALL steel that has been welded not alloy, only the door skins and the extra short section of the extra cab ( rear of door) and roof are alloy.

stop a landi rusting??he he he he he...impossible..keep it out of contact of all moisture..for ever,from when it was born..otherwise watch it rot...

p.s. live in london uk..and there are NO rust/corrosion free landies here..

oh and its the stel not the ali that corrodes first,whatever the theory books might say.(i have 3 landies parked out front,and its the steel body parts that go first.ie sills....the ali panels just bubble up the paint,then develope small white corrosion filled holes,once that has happened you will never stop it..)

zen wrote:stop a landi rusting??he he he he he...impossible..keep it out of contact of all moisture..for ever,from when it was born..otherwise watch it rot...

p.s. live in london uk..and there are NO rust/corrosion free landies here..

oh and its the stel not the ali that corrodes first,whatever the theory books might say.(i have 3 landies parked out front,and its the steel body parts that go first.ie sills....the ali panels just bubble up the paint,then develope small white corrosion filled holes,once that has happened you will never stop it..)

Rust is nowhere near the problem here as where you are.

oh and you have missed the point of the original question

Aluminium is more corrosion resistant than steel as you said. The theory books don't say otherwise.

This is because the oxide that forms on the surface protects it. This oxide is the basis of anodising surface treatment of aluminium. Nearly pure aluminium forms a better oxide surface and some sheet alloys are rolled with a thin layer of nearly pure aluminium on the faces (ingots are laminated before they are run through the hot mill).

But bare aluminium will corrode where it is in contact with bare steel when moisture is present.

It is common to use zinc and aluminium to coat steel (eg. zincalum). The coating prevents moisture contact, but if it becomes damaged, the coating corrodes sacrificially to the steel.

How can a rangie rust with all the factory oil leeks......

You can try a product called Corrosion-X.. Spray it liberally in all seams of dissimilar metals.

takearidewifme wrote:How can a rangie rust with all the factory oil leeks......

The oil leaks only protect the lower part of the vehicle.
(chassis, drivetrain, sump. gearbox, Txfer, diffs, blah blah.

It's all the other stuff above knee height that has the problem!

I understand that you guys are covering the major factors here, BUT, it is electrolisis that causes the corrosion, so what about the what about the electronic rust prevention systems? They seem to work on all other applications.
I have done a ute conversion on my beast and was going to give it a try.
Carl.