What corrodes aluminum?

OzJavelin · 30-07-2013, 06:58 PM

I just noticed my wife's horse float had what looked like corrosiön on the aluminum "guard" over the front of it. On closer inspection I noticed the guard has been corroded right through, including the body?

I don't really care about the trailer, but I'm concerned the FG ute she tows it with, as I'd suspect whatever is over the float probably came from the road while she was towing it with the ute. Had a quick look under the ute and can't see any marks like the ones on the float?

I'm assuming it's probably not something like salt because aluminum doesn't corrode from salt does it? Any chemists out there?

(BTW don't live near the sea .. Havent driven thru water, etc)

Nikked · 30-07-2013, 07:03 PM

Is the corrosion in a specific spot, like around a inner frame etc?

Aluminium will corrode if it is in contact with other ferrous metals...

mcnews · 30-07-2013, 07:05 PM

Yep dissimilar metals always a huge problem for alloys. As in where one type of metal is in contact with another type of metal, and then to make things worse the washer is then made out of yet another material again to make things even worse again.

babyf6 · 30-07-2013, 07:43 PM

http://www.clihouston.com/knowledge-...corrosion.html

hope this helps

Thornie · 30-07-2013, 07:50 PM

I feel bad, I make the **** and I cannot answer your question lol.

MNM96 · 31-07-2013, 08:00 AM

Quote:

Originally Posted by Thornie

I feel bad, I make the **** and I cannot answer your question lol.

Hey Thornie, I am with you, same problem. And am just over the fence at QAL! lol

That said, Caustic Soda corodes aluminium.

burnz · 30-07-2013, 07:59 PM

Quote:

Originally Posted by OzJavelin

I just noticed my wife's horse float had what looked like corrosiön on the aluminum "guard" over the front of it. On closer inspection I noticed the guard has been corroded right through, including the body?

I don't really care about the trailer, but I'm concerned the FG ute she tows it with, as I'd suspect whatever is over the float probably came from the road while she was towing it with the ute. Had a quick look under the ute and can't see any marks like the ones on the float?

I'm assuming it's probably not something like salt because aluminum doesn't corrode from salt does it? Any chemists out there?

(BTW don't live near the sea .. Havent driven thru water, etc)

check the earth wire in the harness, its possible the earth was supplied by the tow ball itself.

bad earth kills alloy.

b0son · 30-07-2013, 08:41 PM

Quote:

Originally Posted by OzJavelin

Any chemists out there?

caustic soda

**ebxr8240** · 30-07-2013, 09:15 PM

Galvanized steel and alloy is bad news..
Sounds like metal corrosion ??
Can also be electronisis..
Esp if there's white powder like substance ...

Pedro · 31-07-2013, 03:48 AM

Quote:

Originally Posted by ebxr8240

Galvanized steel and alloy is bad news..
Sounds like metal corrosion ??
Can also be electronisis..
Esp if there's white powder like substance ...

Yep, aluminium guard connected to steel frame = electrolysis

XP6 · 31-07-2013, 03:04 AM

Yep caustic soda and heat

Shambles · 31-07-2013, 08:38 AM

Anything you can do to stop dissimilar metals from touching directly will help. When you put steel bolts through aluminium use a little light grease. What is occurring is galvanic corrosion, the process where dissimilar metals act like a battery with the presence of a liquid. The aluminium being lower on the galvanic scale will corrode. Ensuring that the panels are electrically bonded to the rest of the structure will help as well. Any corrosion can be removed and neutralised with dilute phosphoric acid. Just be sure to reprotect the metal again with paint.

FGII-XR6 · 31-07-2013, 09:35 AM

instead of regular grease silicon grease provides better protection due to it's high dielectric properties

Quote:

Originally Posted by Shambles

Anything you can do to stop dissimilar metals from touching directly will help. When you put steel bolts through aluminium use a little light grease. What is occurring is galvanic corrosion, the process where dissimilar metals act like a battery with the presence of a liquid. The aluminium being lower on the galvanic scale will corrode. Ensuring that the panels are electrically bonded to the rest of the structure will help as well. Any corrosion can be removed and neutralised with dilute phosphoric acid. Just be sure to reprotect the metal again with paint.

ebv8 · 31-07-2013, 08:55 AM

can you use a sacrificial anode like what they run on outboard motor legs? you can buy them from any boating store and bolt it through the alloy. these are supposed to corrode first and be replaced when needed

FGII-XR6 · 31-07-2013, 09:23 AM

an easier question would be what doesn't corrode aluminium, aluminium is fairly reactive and corrodes quite easily, just because some aluminium on a trailer has corroded I wouldn't automatically assume the worst for your car as it is steel. This is one reason I have never been able to understand the move to alloy body panels on cars

big_landau · 31-07-2013, 09:26 AM

salt air! i have seen places on the coast where the salt air has totally corroded the aluminium windows from houses/units etc.

ford71V8 · 31-07-2013, 10:21 AM

Take a look at a Galvanic Chart.
You'll see Al is right up there

Here's a PDF I just found‎

http://npfasteners.com/pdfs/galvanic...sion-chart.pdf

**supershifty** · 31-07-2013, 10:28 AM

I'm no metallurgist and I agree with the above possible causes. You mentioned that this has occurred on a horse float - without me seeing where the corrosion is, could it be urine from the horses coming in contact with the aluminium? Just a thought.

Cheers!

**Silver Ghia** · 31-07-2013, 10:58 AM

Quote:

Originally Posted by supershifty

I'm no metallurgist and I agree with the above possible causes. You mentioned that this has occurred on a horse float - without me seeing where the corrosion is, could it be urine from the horses coming in contact with the aluminium? Just a thought.!

Good thought. Horse urine residue definitely promotes corrosion in aluminium. Maybe the float has been hosed out on occasions with the water contacting the frame, this would certainly accelerate the corrosion process.

Years ago I was with an airline that carried horses in horse box pallets in freighter aircraft, the boxes were lined to prevent any spillage onto the aircraft structure, but the aircraft floor structure and bellies were always badly affected by corrosion and having to do extensive repairs at each overhaul.

mik · 01-08-2013, 03:19 PM

even water can corrode aluminum(usually when wet for extended periods), , the floor on my truck was like swiss cheese,
also electrolysis as already mentioned, i seem to remember water running off rubber onto aluminum can also cause corrosion, i remember that from 30 plus years ago(not bad for an old codger

).

Addz08 · 01-08-2013, 03:27 PM

Lime... From road base at roadworks..

BOOSTEDGAZ · 01-08-2013, 06:51 PM

I used to build Aluminium superyachts and even with marine grade alloy, sacrificial panels etc the alloy had a limited life expectancy of aprox 7 - 10 years off memory so normal alloy will easily corrode over time due to acids, alkili's and electrolysis etc.

**ebxr8240** · 01-08-2013, 08:21 PM

Plenty of GOOD etching / priming paint, rubber, sikaflex between joins to steel..
Keep in mind the top half of Queen Mary [one of them ships?] is alloy and it needed attention big time..
Some graphite grease or electrical jointing compound to keep water out..
At the same time have all panels electrically bonded to prevent electrolysis.
Sacrificial alloy mainly works in water..
Wash area with kero once or twice a year to wash out water..