Thread: Aluminium problem

God day everybody. I have a problem. On the photos you can see aluminium parts that were on the outside in South Australian rain and shine for 8 years. Aluminium turned into powder. These aluminium parts were from overseas, not local Australian made.
I have a question. What can I use to paint aluminium parts or use any other form of top coat to avoid these problems in the future.
Thank you for your time.

I would have them powder coated

Hi Barnes3, Guys,

At this late stage I would replace them ! Powder coating as Eskimo says will protect the aluminium, but do the welding first. I would also grease the steel bolts well, that is assuming that you can get them out without breaking them !

Originally Posted by BaronJ

Hi Barnes3, Guys,

At this late stage I would replace them ! Powder coating as Eskimo says will protect the aluminium, but do the welding first. I would also grease the steel bolts well, that is assuming that you can get them out without breaking them !

Dont believe everything I say....lol.

I like the Wattyl 'killrust' system of paints. Visit an outlet and discuss with them. They will probably recommend an etch primer for the Al and then a top coat, but see what they say.

I'm a bit concerned by the steel bolts used to attach the Al post to what looks like an Al plate. Even if you are not remotely near the sea, pollution in the air will set up a galvanic cell and make any corrosion worse. Personnnaly I would replace those angle pieces and weld the replacements to the pipe rather than bolt them. Extra effort, but less likely to result in corrosion.

Michael

Powder coating is not a good thing outdoors.
It serves alright for a time, but will eventually fail in an ugly way. And you can't repaint it.

Could be the alloy has too much zinc or magnesium in it?
If possible, a reliable solution to this problem is to get new brackets that aren't prone to corrode, like hot dipped galvanised steel.

What we are looking here at, is a combination of bimetallic and electrolytic corrosion. If it was up here it in Mackay, it would last only half that time.

The aluminum angle sitting flat on the concrete is big part of your problem.There is an electrolytic flow between that concrete and the aluminum.

Concrete passes electrical current, even the very small amount present in this electrolytic corrosion process.

My suggestion to you, is to place a non current carrying "spacer" between base angle. A bit of Delrin sheet would be ideal. However that is a bit costly and you may still have to chase around after it. Instead, buy your wife a new plastic cutting board and steal her old one.

Cut to shape,this board ,several millimeters thick, will provide a cheap but effective way of reducing the electrolytic part the corrosion. Go easy on drilling the old board-they do get brittle.

But wait! You are not finished yet.There is still the bimetallic corrosion problem to deal with. Replace those plain steel hold down bolts (acting much like sacrificial anodes) with some stainless fasteners .

Also a coat of Never Seize on the threads and add some nylon washers between the bolts heads and the aluminum interfaces. There will be a corrosion (but,on a smaller scale ) over time, around these surfaces if you don't.

Yes! it is a bit of stuffing around,but will greatly reduce the corrosion.

I do not believe that just powder coating and new bolts on its own will cure the problem.

I hope this helps you.

PS I took another look at your photos and noticed the concrete surface. I wonder if the concrete has been mixed with river sand containing salt that has not been properly washed out . The concrete seems to have the appearance of salt affected concrete I have encountered in the past.It can be difficult to tell from a photo against seeing it in person.

Grahame






i

Based on the photos this would appear to be galvanic corrosion, if so then electrical isolation between the dissimilar metals steel / aluminium would reduce the effect, as others have mentioned a good paint on both surfaces and a coating of straight grease on the bolts / nuts would help reduce the effect. Alan.

Hi barnes3
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Grahame

You can get jointing compounds that are specifically designed for preventing galvanic corrosion.
The ones I've used on aluminium are typically Zinc Chromate based, one particular product name is Duralac.

Make sure the brackets are made from a marine grade aluminium that is intended to behave nicely in corrosive environments. The ones you have there remind me of what we used to see with 2xxx and 7xxx wrought sections on aircraft. The corrosion breaks it up into layers and travels along the length of the material grain.
Anything you can do to prevent the bolts coming into contact with the air/moisture will help too. if you can seal them up in the bottom of the tube or at least give them a good coating of something as well as paint or seal the heads/nuts will help.

If you just need it done and don't have the materials/time to do it properly then just do what you can and buy a can of corrosion preventative spray such as Lanotec and give it a good dose every 6 months or so.

Steve

Originally Posted by OxxAndBert

You can get jointing compounds that are specifically designed for preventing galvanic corrosion.
The ones I've used on aluminium are typically Zinc Chromate based, one particular product name is Duralac.

Make sure the brackets are made from a marine grade aluminium that is intended to behave nicely in corrosive environments. The ones you have there remind me of what we used to see with 2xxx and 7xxx wrought sections on aircraft. The corrosion breaks it up into layers and travels along the length of the material grain.
Anything you can do to prevent the bolts coming into contact with the air/moisture will help too. if you can seal them up in the bottom of the tube or at least give them a good coating of something as well as paint or seal the heads/nuts will help.

If you just need it done and don't have the materials/time to do it properly then just do what you can and buy a can of corrosion preventative spray such as Lanotec and give it a good dose every 6 months or so.

Steve

Can you recommend a place where I can get a few of marine grade aluminium brackets?

"Powder coating is not a good thing outdoors." with all due respect Rubbish

Hi Grahame.
It's not concrete it's an aluminium plate, old aluminium plate that hang on a 9 meter high radio mast that held an antenna. It has traces of some dirt and bird poo.

I will change the fasteners and nuts to stainless ones. Since the mast was standing in my friends back yard in high winds some of the old nuts became loose.

I wonder if welding the new nuts to new bolts will also help the structure stay intact for longer. What you think?

My friend will receive a new antenna from UK soon and he wanted me to help him fix his mast.

Will painting the whole mast help? He wants to use the old mast which is free of corrosion in the meantime?

I will post some picture of the whole structure a bit later today.

Originally Posted by barnes3

Can you recommend a place where I can get a few of marine grade aluminium brackets?

I can't think of anywhere you'd get them off the shelf.
Have you got any boat builders locally, or an aluminium fabricator? They might have some extrusion that you could make some from, or be able to fabricate some for you from flat (either bent or welded).

Steve

Originally Posted by nadroj

Powder coating is not a good thing outdoors.
It serves alright for a time, but will eventually fail in an ugly way. And you can't repaint it.

Could be the alloy has too much zinc or magnesium in it?
If possible, a reliable solution to this problem is to get new brackets that aren't prone to corrode, like hot dipped galvanised steel.

My friend tells me that the brackets were sent with the antenna from Eastern Europe, so unfortunately he doesn't have any info about the alloy used here.
Do you think that it would be wise to put some nylon spacers between

hot dipped galvanised steel and aluminium?