aluminium and steel trailer corrosion questions

[zagan]

I was witing for one of the rover boys to pipe up, the ting most people have missed it the electrolite (could be a different name?). eg a lead acid battery is nothing with out the acid to carry the electrons.

Sam if you were to park the rover in salt water, if the ally was unprotected it would corrode rapidly. The salt water would be the electrolite.

Some one feel free to correct me as this is from memory on the unimportant stuff in my head.

If you were to place steel n ally together in a clorine base sanitiser you can fisically see the ally boiling off.

It's not the salt water that rusts the ally near the ocean but the chlorine in the air, it keeps attacking the ally and doesn't stop so once it's thru the 1nm of skin layer then the ally will start to rust.

The other thing to note is that a lot of people are saying ally and stinless will cause the ally to rust out quicker, but depending on the kind of stainless you use you can actually stop rusting happening all together or the ally will attack the stainless instead.

stainless isn't listed on the same terms as the other metals on the galvanic list, due to the way stainless steel is produced.

You can heat up ally to help reduce or stop rusting forming as this can increase 1st layer or produce a 2nd skin layer, there's other things you can do as well.

Ally sometimes produces a white powder but this is actually a 2nd skin layer forming, zincalum does the same thing.


The quickest rusting ofally I've read is a welding shop in the UK that was making boat beacons, they use 8mm ally plate and they would replace them every 3-4 years because the ally had around 3mm eaten out of the surface.

[chunderlicious]

it will take many moons longer to corrode alluminium as the corrosion proccess actually includes making the product which protects it from oxidisation.

by joining steel and aluminium you will get that white stuff on the alum, same as if you use it on salt water, its what protects the metal.

[chimpboy]

Damp dirt can be an electrolyte too.

I wouldn't worry about it too much with a trailer but the electrolytic corrosion thang is still good tech when putting an aluminium radiator in a steel-bodied vehicle, or putting steel bits on an all alloy-engine etc.

The reason I wouldn't worry so much with a trailer is that you will be able to see any problems with the naked eye, in plain view. It's when there could be corrosion you can't see easily that I'd take the extra precautions.

Just my thoughts.

[ctguru]

wow looks like i opened a can of worms

if i use aluminium for the tray, should I use 3mm checker plate or 1.6mm steel?

cheers

[V8Patrol]

Depends on the application.......

You havent mentioned the size or use for the trailer
a 6x4 that is used to take garden waste to the tip would be a differant kettle of fish when compared to a car carrier or a trailer for carrying a couple of cows to the market ........


Are you just covering the floor or is this a full tub / tailgates / floor and muguard replacement ????

In which case what about the joining of the guards to the tub..... can you weld the alloy or are you intending to bolt / pop rivet it together ??????
Same applies to the tailgates.... specifically the hinges and locking points


The biggest issue is, which you've allready stated, is the thickness......

alloy is light

but you need to have a far thicker alloy for strength when comparing it to the same job mild steel would do.....
in which case........ you arent really saving on the 'weight factor'


& 3mm chq alloy plate WILL cost lost more than 1.6 mild steel

[chimpboy]

I seem to have noticed that the ally checker plate tends to get "gouged" a lot in trailer floor/truck bed applications. ie it is thick enough to be as strong as steel, but it's still a lot softer so if you put some heavy metal object on there, you will get damage to the aluminium surface in the form of nicks, gouges, etc, and sometimes sharp bits of aluminum sticking up a little too.

I suppose it doesn't matter but I personally don't like it. It's just something I've noticed. So I would prefer steel.

[KiwiBacon]

can i use aluminium plate for the sides of a painted steel framed trailer without causing any corrosion problems?

3M make a double sided foam tape specially for this. It's what they use to hold the skins on camper vans and buses these days. It's what I plan to use when I eventually get around to making my own trailer.

They also have the advantage of stopping any rattles and not having dissimilar metals and paint flaking off one first like pop rivets can cause.

[Patroler]

So everybody saying that you carnt attach aluminium to steel because of electrolysis is absolute rubbish.

yea, you probably won't be around to see it fall apart!

Electrode Potential at 77 F (25 C)

Anodic end (this is where the corrosion occurs)
Element Standard Electrode Potential (Volts)

Lithium -3.045
Potassium -2.920
Sodium -2.712
Magnesium -2.340
Beryllium -1.700
Aluminum -1.670
Manganese -1.050
Zinc -0.762
Chromium -0.744
Iron; Mild Steel -0.440
Cadmium -0.402
Yellow Brass -0.350
50-50 Tin-Lead Solder -0.325
Cobalt -0.277
Nickel -0.250
Tin -0.136
Lead -0.126
Hydrogen reference electrode 0.000
Titanium +0.055
Copper +0.340
Mercury +0.789
Silver +0.799
Carbon +0.810
Platinum +1.200
Gold +1.420
Graphite +2.250
Cathodic end, passive - (no corrosion here)

With this table above if you put two of the metals together there will be corrosion, this will happen on the less noble metal or the anode, the more noble metal or cathode will remain intact and actually be protected from corrosion by the anode - hence the term sacrificial anode - some underground cables and pipelines actually have these especially when theyre expesed to salt water, just bolt a block of magnesium to the steel pipe and the steel will last longer at the expense of the magnesium.

corrosion will occur much more readily when there is a large difference in potential between the metals.

to prevent this, coating or plating the metals can be used, and i'm pretty sure something like aluminium which even uncoated will form a protective layer of aluminium oxide will be slow to corrode, being in contact with steel may just speed up the process of building up its oxide layer.

[me3@neuralfibre.com]

Most of the corrosion stuff listed relates to wet marine environments.

If it's not immersed, the behaviours change radically.
Thats why there is so much debate re. the electronic rust thingies. THey work a treat on wharves and other wet things, On cars however, the debate continues.

I wouldn't worry. My car trailer is alloy & steel now. I use sikaflex, as that's what the semi's use on their decks.

Paul

[date]

It seems that I opened a big can of worms with my initial treatise on electrolysis. For a trailer, it is not likely to be a problem unless it is continually subject to wet conditions - the water being the electrolyte. Yes - it will corrode the steel because the aluminium sets up its own oxide coating on its surface and that is more noble than the raw steel. Incidentally, stainless steel against carbon steel will eventually do the same thing, albeit a lot slower because the galvanic voltage levels are closer and hence the driving force for the current is less.

If the items are painted well, the paint will act as an insulator and you shouldn't have too many problems. If you get relative movement between the frame and the aluminium panels, then the paint layer(s) will break down and you could have problems. Just keep an eye on it. Land Rover panels don't corrode - their frames do, but LR generally put an insulating layer of paint before they roll the panels over the frame. Also, the frames are generally not subject to too much moisture.

[macca81]

i was looking in my engine bay today, and started thinking about this subject...

my engine block is steel, my head is alloy, my turbo and maniafold are alloy, all of the blots holding these things to the steel block, are also steel. for 15 years there has been no corrosion problems...

[chunderlicious]

macca, your block is cast iron and the head is alloy, it is seperated by a gasket, same with everything on a motor. the only thing that touches is a bolt and youll find they will have rusty threads. except the exhaust manifold bolts which will be rusty on the outside but the thread will be fine.

[KiwiBacon]

macca, your block is cast iron and the head is alloy, it is seperated by a gasket, same with everything on a motor. the only thing that touches is a bolt and youll find they will have rusty threads. except the exhaust manifold bolts which will be rusty on the outside but the thread will be fine.

The coolant is creating electrical conduction with everything it touches. Block, head, radiator etc.

[chunderlicious]

meah. i sounded right till you came along

[MART]

ctguru , your looking for weight reduction , 1.6 on the side wall and 3.0 mm on the floor , if you use 1.6 mm on the floor you will need more supports to stop the floor buckling so 3.0 mm would work lighter in the long run. As for the corrosion factor I would use 3/16 stainless blind rivets , they will outlast both the metal and ally and in your lifetime , unless your building a trailer for a submarine you won't have a problem. You can also use a non acidic silicon between the panels to make it water tight. Clamp you panels in position , drill all the holes and then remove it , clean all the swarf away , then re-attach , thw swarf from drilling caught between the panel is the main cause of rust , Cheers Paul.

[ctguru]

cool sounds good, using it for towing an atv and have found some 2.1mm treadplate for the floor

thanx for all you help