That's almost like asking "what is glue?". There are a number of
materials that can be used to solder aluminum. Some will work well on
other metals too. Most require a flux designed to work with them on
aluminum. Bond strengths vary quite a bit.
Tin solders Al just fine. A good flux must be used to keep the oxide off
it is often placed on and then through it, scrape a section through the Al
and then the solder will mix.
Often you can find silver boxes in hardware stores - small rolls of it with
the special flux.
Martin
Martin Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder
brassbend wrote:
Depends on what it is...
Aluminum solder is anything that wets aluminum. This includes most metals
on the periodic table with a melting point less than aluminum's. Zinc, tin,
gallium, mercury and some of the alkaline metals (maybe just lithium). The
heavy white metals thallium, lead, indium and bismuth probably don't stick
too well. Gallium and mercury amalgamate (aluminum amalgam is used in
various chemical reactions), but they just weaken and oxidize it at room
temperature. Cadmium is similar to zinc so may wet it well, but it is more
of a "heavy metal" than zinc, so may not.
Of the "good" metals, zinc and tin are the cheapest and thus most practical.
Coincidentially, they happen to be the most used. Pure tin, maybe with some
copper or silver to strengthen it, would work well enough. Lead-tin may
work, the tin holding it to the aluminum. I've done it before, but due to
the poor joint (I don't have the fluxes), it's hard to say how well it
works.
As for zinc, it alloys very well with aluminum so is more like brazing, and
as a matter of fact its melting point is somewhere around 800°F so it's
pretty much brazing by definition anyways.
The "magic solder" stuff that comes with a flux (probably based on corrosive
fluorides) and melts at a low temperature is probably tin and zinc, possibly
with cadmium and lead. The "miracle rod" product that "doesn't" require a
flux (because you rub the rod against the work to break the oxide) is either
pure zinc or an alloy with up to 12% aluminum.
Tim
--
Deep Fryer: a very philosophical monk.
Website:
Here are some thoughts:
Tin the aluminum under oil, then solder as normal.
Aluminum normally won't accept regular solder. That's because
of the oxide coating on its surface. By covering the surface with
oil, you can scrape away the oxide coating while preventing oxygen
getting to the surface and reforming it. You can then tin the surface
with an iron, through the oil coating, and get a proper bond. Then
you can clean the oil off and solder as usual.
This is a home shop technique. There are probably better solutions
in a production environment.
Gary
Gary Coffman KE4ZV | You make it |mail to snipped-for-privacy@bellsouth.net
534 Shannon Way | We break it |
Lawrenceville, GA | Guaranteed |
Aluminum solders are indeed made specifically soldering aluminum to
aluminum, and in some cases aluminum to other metals. Materials that
contain aluminum, as Allstate #31 and others, are higher-temperature
brazing materials.
The Kester "aluminum solder", found at a hardware store in the silver
box, is tin.
Harris Staybrite is 96% tin, 4% silver. They say it'll stick to
aluminum with a special flux, but my welding store doesn't carry the
flux so I can't vouch for that. It will also stick to brass,
copper, steel and stainless.
Allstate "Strongset 509", a zinc- cadmium alloy, will join aluminum to
aluminum, also to copper, brass, steel and stainless steel. It's
quite strong at 29,000 PSI. It's pricey. The flux is organic and
burns easily. This stuff works very nicely if one can avoid burning
the flux. If the flux burns, it's a mess: clean up, start over.
Dang, I just learned tonight that they recommend applying the flux to
the solder then applying the solder to workpiece that is hot enough to
melt it. Geez, I never thoughta that! I'll be trying that
tomorrow.
Allstate 107, a "silver bearing alloy" (they don't say with what)
will also join aluminum to aluminum, copper, brass, steel and
stainless -- but it isn't as strong at 20,000 PSI. "Commonly used to
join aluminum wires to copper lugs." It sounds a lot like Harris
Staybrite so it's probably tin-silver.
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offers a couple of aluminum solders and companion fluxes. He doesn't
say what's in them. Everything I've tried from him has worked well.
There are others, but all that I know of are similar to one of those
mentioned above.
Use of the recommended flux is very important with any of these
materials. Wrong flux = lousy results.
I have several rolls of "alu-sol" multicore solder. Says "solders
aluminum, most aluminum alloys, and other metals. No additional flux
required"
Data sheet says tin/lead alloy with tin/zinc amine flouride complex -
whatever the heck that means.
It works.
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