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Old 27th September 2011, 10:04 AM   #1
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Join Date: Jun 2011
Default Soldering Aluminium

Hi,
I am sorry if this has been covered in the past but I couldn't find it on a quick search.

I have been reading a few posts and noticed that people are saying that you cannot solder aluminium - well you can. Further, there is no need for special solders or fluxs. All that is necessary is:
  1. a soldering iron/torch with sufficient heat output,
  2. course emery paper,
  3. some solder,
  4. a scraper (optional), this is just a small piece of steel with a sharp chisel like edge about .5 -1mm across. I have used many things, but currently I use one of those really cheap small jewelers screwdrivers, sharpened up and bent over.
  5. and a brush (optional).

Lead/tin and tin/copper solders bond to aluminium very well but they do not stick to aluminium oxide. The problem is that a very thin layer of aluminium oxide forms (virtually) instantly on any aluminium that is exposed to the air. The obvious solution is to keep the air from new aluminium so that the oxide does not form.

The easiest method to do this is the submerged joint. In this method, form a bead of hot solder over the spot to be soldered, then using the scraper remove the aluminium oxide on the surface that is submerged under the solder. The solder will immediately bond to the newly exposed aluminium metal The steps are:
  1. Clean the aluminium with course emery paper until it is very clean
  2. Use an iron/torch that is powerful enough to melt solder on the aluminium while overcoming heat loss due to aluminium's high conductivity. Fully preheat the iron
  3. Apply heat to the correct area getting the aluminium hot while forming a puddle of solder. The solder will form a bead and try to stay with the iron.
  4. Get your scraper, push it into the blob of solder and scrape it along hard enough to scrape off some aluminium (you will quickly get the hang of it)
  5. When you think you have 'tinned' the aluminium, keeping the solder hot, use the brush to brush away the puddle. You will easily see where it is tinned and where it is not.
  6. You are finished, you can now solder anything to the tinned sections.
A simpler method for people who don't care about their soldering irons. Sharpen the soldering iron tip to a wedge, follow steps 1 to 3 and then just raise the back of the iron and use the tip to scrape off the oxide - done. After a while you just "know" when it is done right.

Some 37years ago (arrrghhh) I did a lot of soldering of copper wire to aluminium in the field using this method with just a soldering iron and solder - worked perfectly. Although, since I constantly had to file the soldering iron tips to keep them sharp, I went through a lot of soldering iron tips but they were cheap plated copper tips.

Some other ways. If you want a really good joint, form a pool as above and use a small twist drill to remove little pits of aluminium under the solder. Be aware however that this is not as mechanically strong as a flat lap joint.

You can sweat bolts into aluminium using this method. Drill the holes slightly undersize, heat it all up (including the correct size twist drill bit). Fill the hole with solder slowly run the drill down the hole, the solder should stick to the sides. When soldering the bolt in, it is best to have a smooth surface, not the threaded surface (unless it is an interference fit). I did one of these once and tested it to destruction The brass bolt failed tensile/torque before the solder joint gave up.

Notes:
  1. I use very course emery paper to create a lot of ridges, when scraping under the solder it is much easier to scrape off the ridges than to scrape off a flat surface. True only the ridges will the soldered but if you don't think it is good enough just keep scraping.
  2. If the joint does not have to take a lot of mechanical load, then surprisingly small areas will give you a really good electrical joint (testing from the dark ages).
  3. If you are jointing really large areas, those very small, fine, steel, wire brushes are really good scrapers - watch out for the sticking solder, a good thump usually gets it off the brush.
  4. Although every aluminium I have tried has soldered well, I give no guarantees about the thousands of other alloys.
  5. These joints are both mechanically and electrically good. However, I have not investigated any galvanic problems except for a specific instance (joints had to be kept airtight).
  6. If done properly, mechanical joints can be very strong, the only way you will get that tinning off is to grind it away. The joints will break well before the tinning lets go. Properly sweated interference joints are a joy to behold. Remember that the thinnest joint is the strongest joint, the solder is the weakest link.
  7. I have tested this method with various lead/tin solders, tin/copper (98/02), and some higher temperature silver content solders. All have been successful.
  8. I have managed to do this successfully with relatively thin foils, it is possible but requires a fair bit of practice ( I still use the emery cloth, not so course and very judiciously). If whatever is being build with foils is complex, I suggest you tin it first before putting in all that effort
The pics are just to prove that it can be done.

We are currently camped just north of Adelaide in the motorhome - off grid. I only have a small soldering iron in the motorhome, just big enough for running repairs. The cut in the aluminium is only there to reduce the heat losses enough that the soldering iron could melt the solder. The resistance of the joint was 0ohms, the value displayed is just the residual of the multimeter and leads. Yeah I know, but for $7 the meter is surprisingly accurate. I have 4 of them.
The joint shown is extremely strong, even though it was done by just rubbing the side of the iron through the solder against the aluminium, no other scraping was required.

Regards,
Bob
Attached Images
File Type: jpg resistance test.jpg (104.8 KB, 885 views)
File Type: jpg strength.jpg (45.5 KB, 840 views)

Last edited by bobnick; 27th September 2011 at 10:11 AM. Reason: Server updating mutilated the posting
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Old 27th September 2011, 10:47 AM   #2
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Interesting.
I once bought wire with composite structure (copper, aluminum and other metals like bronze) and got a special solder with it that was supposed to solder to the alu wire strands too.
That was hard.
This looks like a good way, also to earth separate plates in a boxed enclosure.
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Old 27th September 2011, 10:56 AM   #3
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Use this it really works

H&N Electronics Soldering Flux
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Old 27th September 2011, 12:07 PM   #4
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Thank you for the wonderful tips.
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Old 27th September 2011, 12:40 PM   #5
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Interesting I have found this to be true as well ,But it is still a pain.
Have you ever tried a product called alumi-weld I have never tried it myself but I have seen a live demo on it and it is amazing stuff.

I have an application where I need to solder wire mesh to a metal frame and aluminium is the material of choice as it is cost effective,But I haven't found an efficient way to do this yet.

Do you have any suggestions?

jer
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Old 27th September 2011, 01:23 PM   #6
oshifis is offline oshifis  Hungary
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Bob,

Is it possible to do the same trick under resin flux instead of under solder blob?
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Old 27th September 2011, 04:08 PM   #7
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Quote:
Originally Posted by oshifis View Post
Bob,

Is it possible to do the same trick under resin flux instead of under solder blob?
You could do it under any material that precludes the air and isn't damaged by the heat. I don't like flux much, even the core flux in electronics solder. I think this came about as I did a course in high reliability soldering up to the aerospace level (I was not in aerospace and still don't know why I was selected to do it). In these courses flux was as much (or more so) your enemy as friend. Anyhow, the solder blob is the most direct method, the aluminium is tinned in one step, you can reuse any unused solder as the contamination is minimal and we are not in space!. Give it a go, it really is easy.
Regards,
Bob
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Old 27th September 2011, 04:36 PM   #8
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Quote:
Originally Posted by geraldfryjr View Post
Interesting I have found this to be true as well ,But it is still a pain.
Have you ever tried a product called alumi-weld I have never tried it myself but I have seen a live demo on it and it is amazing stuff.

I have an application where I need to solder wire mesh to a metal frame and aluminium is the material of choice as it is cost effective,But I haven't found an efficient way to do this yet.

Do you have any suggestions?

jer
Hi,

Sorry but I can't quite visualise what you are trying to do. Which parts are aluminium and what sort of mesh? I suspect that this technique is not applicable.

Since I learnt this technique all those years ago, I have become somewhat of a fanatic. It is surprising how many problems it has solved but it is also quite limited.
I mainly posted it for those members who may want to do the odd aluminium solder job once in a while, such as wiring of ES panels and making earthing points on aluminium but don't want to buy specialised materials or can't wait. I have used it to to fabricate parts but only to annoy other people.

One big advantage is that you don't have to worry about cleaning up the flux or flux inclusions. You can get (often do get) aluminium oxide inclusions but these pose no long term problems and don't degrade the joint in any meaningful way.

Regards,
Bob
Sorry, I didn't really answer your question. I think you will have to use an aluminium flux and suitable solder if you wish to fully solder it. Otherwise you could use another method of attaching the mesh and use small solder joints for electrical connection. Sorry, more info required.
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Old 27th September 2011, 07:46 PM   #9
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I use aluminium window screen that is either Powder coated or painted with clear acyrlic for the stators of my ESL panels.
Here are some sample photo's,

Material for ESL

And rather than using plastic egg crate material for support I decide to try and make a frame out of some 1/4" X 1/2" U rail and it was perfect and neat until I tried to solder the thing together.
I tried every type of solder and flux to I could get my hands on.

The last time I had tried to do this it took me over an hour and alot of propane to get a nicely tinned 1" strip on top of a rail.
I haven't spent alot of time on this as it was quite fustrating as the parts weren't clamped down and were hard to work with as they get quite hot .He,he
But I figured once I got the surfaces tinned the rest would be a breeze.

After that I went and got a cheapy TIG welder for like $200 but I never had the chance to get a tank of argon for it yet as a large tank is going to run me about $175 plus the gas and a regulator yet.
I'm sure that it will work nicely but it is more than I wish to spend at the moment.

Stupid life things had happend as this was only 2 1/2 years after I had built those very panels in the pictures in 2003.

So I'm back to researching the structural side of the project as I have worked out the coating issue's, and,The problems driving them as well.
They perform way way past my expectations now.

Maybe some kind of spot welding technique is another process I have been investigating as well.

Anyway the idea was to mount the screen to the frame so that it will be perfectly flat and have the whole thing coated as a whole.

This would render me a very sturdy product than using the plastic material which bends very easily and requires extra support for panels wider the 8" to keep the panels flat enough for use in an ESL.

Also this would make connection to the unit as easy as a tapped screw hole and/or a spade lug.

This could be done very easily using solderable materials such as copper or brass but the cost goes through the roof then.

If you have any questions reguarding any more detail feel free to ask.
As I have documented every thing about these panels here at DIYAudio but it is scattered in several different threads.

jer
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Old 28th September 2011, 02:26 AM   #10
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I had no idea. I thought aluminum was incompatible. Thanks for sharing!
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