# Copper to aluminum?



## Bill Kahn (Mar 27, 2021)

Any suggestions for what to use to solder copper to aluminum?  I am a newbie and this will be my first (non-electrical) solder adventure.  Thanks.  -Bill


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## Ulma Doctor (Mar 27, 2021)

98%Zinc/2%Aluminum alloys are used in HVAC systems for this purpose


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## SLK001 (Mar 28, 2021)

I don't think that you will be soldering the two materials together, because the temp needed is too high.  However, there are brazes that will braze the two dissimilar metals together, as the Doctor states.

Why don't you tell us what you want to do with the two metals?


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## Bill Kahn (Mar 28, 2021)

SLK001 said:


> I don't think that you will be soldering the two materials together, because the temp needed is too high.  However, there are brazes that will braze the two dissimilar metals together, as the Doctor states.
> 
> Why don't you tell us what you want to do with the two metals?


OP here--The use is a small one-off artistic piece (there is a particular reason why aluminum and copper, not worth explaining).  It will be a 2 inch butt joint on .3" thick plate.  (Actually, six such joints).

I am happy to braze too--I gather the official difference from soldering is just that the melting point of the filler is over 840F.  Of course, need to stay under like 1150F or the aluminum gets soft.

-Bill


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## RJSakowski (Mar 28, 2021)

O have successfully soldered wires to aluminum foil  but nothing as large as the joint you are trying to make..  In my experience, the key is to be able to remove the oxide layer on the aluminum and get down to the bare metal.  Actually, the same is true for copper.  If you have a black oxide layer on the copper, it is impossible to solder.    The difference between the two is that the copper oxide can be dissolved with an appropriate flux while the the aluminum oxide has to be removed by mechanical means.  Also, aluminum oxides very quickly in air.  

If you can manage to tin the mating surfaces, you should be good to go.  Once tinned, the solder will flow into the joint.

Something that I haven't tried but might work is to use an inert atmosphere to  prevent the aluminum from oxidizing.  I am thinking of something like a small glove box and argon gas.  There are also available zinc based brazing rods which will bond to aluminum. again, if you can manage to tin the aluminum with it, you should be able to solder that surface.


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## Janderso (Mar 28, 2021)

You may want to look into Muggyweld


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## brino (Mar 28, 2021)

I have had great success lately with Bernzomatic brazing rods:
https://www.bernzomatic.com/Products/Brazing-Welding-Rods/AL3
They are available many places.

However, both of my projects were aluminum-to-aluminum:
https://www.hobby-machinist.com/thr...-window-regulator-mechanism.91146/post-831738
https://www.hobby-machinist.com/thr...you-make-in-your-shop-today.67833/post-820961

You'd have to test the properties on copper.......

-brino


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## graham-xrf (Mar 28, 2021)

Copper to aluminum is a common need for electrical bus bars to high power furnaces and electroplating plants. The transition from aluminum to copper was by a high pressure cold weld. I can't recall the detail, but I once connected 6mm thick bus bars that used this trick. Search on the net for aluminum copper cold weld.


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## Weld ON (Mar 29, 2021)

Well looks like a have to make some video of exotic welding ...  4 sure i will do ..


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## pontiac428 (Mar 29, 2021)

I think you will have the best results with zinc brazing, as @Ulma Doctor quickly pointed out.  Low temp, with enough adhesion for a low-stress application.  Your plate thickness will probably make it hard to heat the copper with propane, so I'd try oxy/acetylene based on that detail having not seen what you're working with.


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## Weldingrod1 (Apr 1, 2021)

Explosion bonding is the go-to way to join Al to Cu, but it's not home shop friendly ;-)

Welding Al to Cu is really hard to do, and you get yellowish zones that are Copper aluminide and/or Aluminum bronze. Super hard and brittle for the first one... This is a necklace I made for my wife decades ago. I back-end milled grooves in the copper and back filled with Aluminum. I had to grind it flush; milling just didn't work.
	

	
	
		
		

		
			








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