Electronics > Projects, Designs, and Technical Stuff

Soldering Aluminum Wires vs Copper

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DW1961:

--- Quote from: Ian.M on July 19, 2020, 10:58:03 pm ---Grab an offcut with pliers and heat it in a gas flame.  Aluminum melts at 660 deg C (dull red heat) or a bit lower depending on the alloy, and as you approach that temperature will 'flop', sharply bending or even breaking just inside the flame.   Copper melts at 1085 deg C which is barely achievable within a natural gas flame that isn't fed with preheated air and fuel.  It will be at bright orange heat, close to yellow heat, and you'll find that to get that temperature it must be in the heart of the flame at the tip of the blue cone.  If you melt from the end of the wire, the molten copper will ball up and form droplets.

For fine or stranded wires, the luminous flame of a gas lighter offers good discrimination - its not hot enough to readily melt copper but is hot enough to cause the characteristic aluminum 'flop'.


Another approach would be chop some up into very short pieces to expose as much suspected aluminum as possible and immerse in a strong lye (sodium or potassium hydoxide) solution in a clear container.  Aluminum will react producing tiny bubbles of hydrogen gas.  Other metals commonly found in wires will not.

You can eliminate the other common 'fake copper' wire easily- copper coated steel is attracted to a magnet and is significantly stiffer than copper or CCA.


--- End quote ---

So are you saying that if you try to solder two CCA wires, it's not going to work, right? I'm asking because I have that 22 AWG "tinned copper" wire and I have some Amazon speaker wire, and I don't trust ANYTHING anymore.

I mean, I just assumed when I saw a roll of what seems to be copper wire, I thought it was copper wire. I guess the rule now is unless it states it is pure copper wire, it's not. It''s the same thing with "gauge" wire. Better make sure it says AWG not just "gauge."
"
I'll use the lighter method to test every wire I buy now. 

I did use that 16 AWG Amazon speaker wire, that looks like copper, to attach two tin alligator clamps to the ends of the wire and it's stuck solid as hell. I tried to pry it off just as an experiment and it's damn well bonded good. I ended up destroying the alligator clip but the wire is still bonded to the clip--lol. Would that be possible it the wire were CCA?

Ian.M:
Personally, I find Aluminum trivial to solder with regular Sn60/Pb40 solder, provided you can get enough heat into it.   With a 100W Weller soldering gun its only a little harder than soldering to tarnished copper.  With a wimpy little long conical bit on a low powered iron you wouldn't have a snowflake's chance in hell of getting aluminum to wet with solder.  Don't use your best bit as you have to rub the aluminum surface through the solder pool with moderate pressure, and that can be hard on the bit plating.  However unlike other aluminum soldering techniques like working under pools of oil and aggressive specialist fluxes, it doesn't immediately mess up your bit, and no special cleanup is required.

What I do is prepare the aluminum surface by abrading with a fibreglass pencil, then I immediately apply liquid rosin R flux* and continue abrading it through the flux pool, which excludes most of the oxygen in the air.  Before the flux has fully dried out, I tin the desired area by forming a small solder pool and rubbing the surface under it with the bit, (to disrupt the very thin oxide layer that will have reformed because the flux failed to totally exclude all oxygen), till it starts to wet, then expanding the wetted area by working outwards adding fresh solder as I do. The solder slightly dissolves the aluminum, so the oxide at the edge of the pool is undercut and its easy to get the tinned area to expand.   I then wipe off the excess solder while still molten, and clean up excess flux with IPA leaving me a tinned area that can be soldered to normally.

You don't get the feedback of the solder freely wetting the metal surface that you get with copper alloys when they reach a high enough temperature, so judging if your iron is adequate and technique good enough takes practice.

If you practice on thin aluminum sheet, you know you've got there when you can bend the sheet across the tinned patch without any signs whatsoever of it lifting at its edges. Once you've mastered tinning aluminum, getting nice joints to tinned aluminum without preheating takes a bit more practice, as the aluminum conducts heat away so fast its easy to get a 'cold' joint.

Here's one I just did to demonstrate on an aluminum coupon cut from a foil takeaway container.  I haven't cleaned up the flux residue from the final stage of soldering a wire onto the tinned patch, so it doesn't look as pretty as it should.  It took longer to get a decent closeup photo than it did to do, including surface preparation, and even longer to type up this post!

* I generally use liquid R flux not RMA or RA, and not a paste or gel flux because used sparingly it can be treated as no-clean, so when working with aluminum, its just what I've got handy on my bench.  Any other high solids general purpose liquid flux would work equally well for aluminum, as long as it forms a tenacious liquid film to protect the aluminum round the edges of the solder puddle from rapid oxidisation.

DW1961:

--- Quote from: Ian.M on July 20, 2020, 05:48:32 am ---Personally, I find Aluminum trivial to solder with regular Sn60/Pb40 solder, provided you can get enough heat into it.   With a 100W Weller soldering gun its only a little harder than soldering to tarnished copper.  With a wimpy little long conical bit on a low powered iron you wouldn't have a snowflake's chance in hell of getting aluminum to wet with solder.


--- End quote ---

I don't want to even mess with aluminum. I'm glad I asked this question. I didn't even know I had to caveat emptor even wire just to make sure it was really copper. Geeze!

I guess aluminum does have better conductivity than copper per weight, but this CCA shit seems like a plague for electronics.

Ian.M:
CCA is solderable *IF* the copper coating is well bonded to the aluminum and reasonably clean.   It only takes a thin 'flash' of copper to prevent the formation of an aluminum oxide layer, and as long as you don't break through the copper when cleaning it, the copper will take solder readily, dissolving in it and letting the solder wet the underlying aluminum.  Corroded or badly tarnished CCA is *MUCH* more difficult to solder . . .


If the price is too good to be true, it probably isn't! Copper is currently just short of four times the price of aluminum, so even with the difficulty of copper plating it there are large savings to be made by the less scrupulous.

jbb:
Another method for finding surprise aluminium wire: drag the end over some fine sandpaper and have a look under a magnifying glass.

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