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Old 02-19-2019, 04:51 PM   #1
eccerr0r
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Default Solder to ... aluminum?

Here's something I haven't seen much good information. How does one solder aluminum -- say simply, aluminum to aluminum (and need good electrical connectivity!) The passivation layer is what makes it difficult. Need some special flux, but what kind of flux is recommended? Or have people simply been scrubbing/mechanical cleaning, though that's not an option for me at this point...
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Old 02-19-2019, 06:55 PM   #2
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Default Re: Solder to ... aluminum?

I have soldered aluminum using ordinary rosin flux, I have also used oil as a flux, Clean the metal, flux and tin each piece, then solder together.
If it is thicker cast aluminum, I use aluminum brasing rod and torch
Practice on some aluminum pie plate strips

Last edited by R_J; 02-19-2019 at 06:56 PM..
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Old 02-19-2019, 07:21 PM   #3
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Default Re: Solder to ... aluminum?

there is solder for that.
it uses different flux.
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Old 02-19-2019, 07:25 PM   #4
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Default Re: Solder to ... aluminum?

Yeah I wish I can clean the metal... I was trying to use solder to reconnect two segments of an aluminum squirrel cage. Removing the squirrel cage from the rotor seems impossible The problem area is in between the ring and the rungs, and separating the two to clean before soldering would be hard. If there was a way to chemically clean (some kind of flux good for aluminum) and let capillary action to suck in some solder, that would be great!

Actually you know what, you gave me a good idea. Thanks: I need to *CLEAN* the metal, as in, scrape enough of it off so that I can squeeze in a bit of copper to replace the removed aluminum. The freshly cleaned aluminum should now be much easier to solder to... I wonder if this would be sufficient to gain conductivity to the squirrel cage once again (and hope that the solder doesn't melt from I*R current going through the rungs...)

stj, yeah, that seems to be the thing... I just don't know where to get this aluminum flux in small quantities, wonder if there are some homemade flux that doesn't have to be great but would do the job?

Last edited by eccerr0r; 02-19-2019 at 07:27 PM..
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Old 02-20-2019, 01:10 AM   #5
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Default Re: Solder to ... aluminum?

read this:
Attached Files
File Type: pdf Solder_Wires_2017_1_small.pdf (1.40 MB, 17 views)
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Old 02-20-2019, 02:27 AM   #6
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Default Re: Solder to ... aluminum?

Sometimes I wonder if I should dump some mercury on it, this definitely will destroy the passivation layer, but it would unfortunately destroy the metal completely

Still kind of hard to tell which one is good for aluminum specifically. I thought I read somewhere that standard fluxes for copper won't work for aluminum, and yes aluminum is hard to solder to, despite copper having as bad-for-soldering thermal conductivity.

Perhaps the luck RJ is having is because the flux is simply keeping oxygen away from the freshly mechanically cleaned joint, if only I could clean the area between the two wires which is no doubtedly contaminated by oxides by now, maybe a mixture of some arcing too...

I have not tried inorganic flux ... wonder if that works better for aluminum.
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Old 02-20-2019, 05:17 AM   #7
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Default Re: Solder to ... aluminum?

the document mentions an Organic flux called s321 that is very active aka corrosive.
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Old 02-20-2019, 09:37 AM   #8
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Default Re: Solder to ... aluminum?

You need to clean the surface of the aluminum first, and yes the flux prevents oxidation while you are soldering. Aluminum will start to oxidize immediately after cleaning. you can't wait to apply the flux like with copper
If you can't get at the aluminum to clean it, nothing will stick to it.
What are you trying to solder?
I found this guide, maybe it can help
Attached Files
File Type: pdf AluminumSolderingGuide.pdf (879.2 KB, 20 views)

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Old 02-20-2019, 11:31 AM   #9
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Default Re: Solder to ... aluminum?

It's this project I've had burning in the back burner forever:
I have a squirrel cage induction motor whose squirrel cage broke--the cage no longer conducts where it needs to conduct. Problem being, I can't remove the cage from the rotor to work on it by itself and thus can only work from the outside layer - places where I can see it.

The cage is made out of aluminum. So I was hoping for cleaning the gap chemically because mechanical cleaning of the gap is impossible without completely destroying the rotor. I suspect even if it were made out of copper, the problem would be infeasible.

Perhaps simply trying to weld the joints back together on the rotor is possible but once again I still need a flux there At least I won't have to worry about the secondary effects of the added resistance of the fillet - all aluminum will conduct more than the solder...and the resistance of solder could heat and melt itself...

(Why this broke in the first place? I have no idea.. think it was initially press connected or something and never soldered/welded?)

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Old 02-27-2019, 09:38 AM   #10
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Default Re: Solder to ... aluminum?

I have had very pore luck soldering to aluminum , like with a few a/c condencers . I took them to a shop and had them tig welded .
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Old 02-27-2019, 11:33 AM   #11
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Default Re: Solder to ... aluminum?

I repaired a high preasure a/c line that had a hole worn through it, I used a propane torch and the aluminum rod that is available for this. It worked perfect and is still working 3 years later, I also used the aluminum rod to repair a larger aluminum casting but need to use a map gas torch, the propane was not hot enough.
This works in many cases, but if it was to repair a broken high preasure line, it may not be strong enough.
However I don't believe a torch could be used for what he is doing.

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Old 02-27-2019, 06:18 PM   #12
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Default Re: Solder to ... aluminum?

I've not really welded before, would think that a flux is needed too?

I have a feeling a small arc welder would actually be the last resort, size permitting. A flame torch probably would not work as it may damage other stuff...
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Old 02-27-2019, 06:37 PM   #13
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Default Re: Solder to ... aluminum?

Why don't you show us what you are trying to repair, maybe someone will have some ideas.
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Old 02-27-2019, 07:02 PM   #14
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Default Re: Solder to ... aluminum?

Well, I'm sure people know what the squirrel cage rotor is. The aluminum rungs in the rotor no longer conduct electricity to the end rings. My assumption is that the unit was press fit together without regards for corrosion over time, but can't discern how to disassemble the unit as it looks like it had been hammered together. But anyway the objective is to make them conduct once more.

I suspect most people claim FRU is the whole motor (it's simply a shaded pole motor)...
I was hoping to reduce the amount needed to be replaced...
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Old 03-24-2022, 08:01 PM   #15
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Default Re: Solder to ... aluminum?

Know what... I wonder, for shaded pole motor squirrel cage motor rungs, perhaps I'm thinking of the wrong solution... why couldn't I just rip out the bad aluminum rungs and put in a new piece of copper wire in its place! Copper should be easily solderable and all should be good once more...

I just wonder what the electrical characteristics through these squirrel cage rungs...
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Old 03-26-2022, 12:37 PM   #16
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Default Re: Solder to ... aluminum?

I haven't tried this myself, but I have heard good reports from them.

https://www.harborfreight.com/8-piec...ods-44810.html
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Old 03-26-2022, 01:02 PM   #17
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Default Re: Solder to ... aluminum?

The tough thing is that the broken section is inaccessible, have to pull the windings out to get to the broken section... and then might well replace with copper?
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Old 03-26-2022, 04:32 PM   #18
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Default Re: Solder to ... aluminum?

project-farm on utube tested the aluminium brazing rods
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