View Single Post
  #5   Report Post  
Posted to rec.crafts.metalworking
Ed Huntress Ed Huntress is offline
external usenet poster
 
Posts: 12,529
Default Soldering Aluminum to Steel

On Sat, 31 Mar 2012 22:31:48 -0500, Tim Wescott
wrote:

On Sat, 31 Mar 2012 22:20:23 -0400, Ed Huntress wrote:

On Sat, 31 Mar 2012 20:40:02 -0500, Tim Wescott
wrote:

This is kind of a product review, kind of a "how to", and kind of a "how
not to".

But mostly, it's a request for the RCM brain trust to review what I've
done and figured out, and to straighten me up if I'm going in the wrong
direction.

Quite a while ago I got a Harris "Al-Solder 500" kit from the local
welding shop. This has some 85-15 tin/zinc solder, some Harris "Stay-
Clean" flux, and a rather alarmingly long MSDS (short story: don't
breath the white smoke).

I got this for the purposes of soldering aluminum ferrules onto steel
music wire, the purpose of the ferrule being to provide a good bonding
surface to a carbon-fiber arrow shaft. With that, I can make pushrods
for control line airplanes that are more rigid and lighter than ones
made all of music wire.

So, partially from inertia, and partially because of the warnings on the
MSDS, I've been making the ferrules from brass because I can solder them
with plumbers solder relatively free from worry.

Today, I went and made some ferrules out of aluminum, and gave the
soldering a whirl.

The first one I tried was completely unsuccessful. The directions
implied that the soldering could be done with a torch at the same time
they mentioned that the flux became inactive at barely above solder
melting temperature. I tried it, with a torch, and things failed
miserably. So miserably, in fact, that I've got a couple of pushrod
ends sitting on my bench right now with brass ferrules.

After I got the replacement ferrules soldered, and as I was cleaning up
the mess, I decided that since the soldering iron was hot anyway, and
since the solder is supposed to work at 450F, I'd try it on the stuff.
So I slapped some flux on the ferrule, put the iron to it, and melted on
some solder. It worked! Rather like magic -- I didn't have to scrape
on anything or do anything special other than not snort the smoke (and
it is evil-looking: there's something about dense, pure-white smoke that
puts me off).

Then once I had a ferrule with solder on it, I took some music wire,
sanded it, and stuck it into the hole with the iron on it. This didn't
make a good bond -- a light whack with a center punch and a piece of fir
1x2 and the music wire came right out. Crud.

But I saw that the bond to the music wire was pretty crappy, so I
slathered flux on the wire, put things together, and tried again. This
time I (probably unnecessarily) made sure to pull the wire out of the
ferrule a bit, to make sure I had solder on it, then pushed it back in.

This second time was much stronger: I did manage to whack the wire out
of the ferrule, but I had to give it a pretty good thump: I'm sure that
the impact I gave it was way more than I'd see in normal use, and if it
happened in a crash there'd be a lot more damage than one cruddy little
solder joint.

So (goodness this is taking me a long time to say), it looks like the
proper technique with this stuff is to treat it like regular solder and
flux, with the possible exception of being very careful about the fumes,
and (also possibly) with the exception that I shouldn't expect the
solder to wick into joints with the enthusiasm that tin/lead solder
does.

Does that sound about right?


I'll limit my comments because I haven't used that solder, nor am I sure
what the flux is. But I have a tip that may help get a better bond on
the music wire.

Tin it with solder before putting it in the ferrule. I've soldered a lot
of steel and I never use anything but a commercial acid flux for steel,
or, when I was in school shop classes, shop-mixed zinc chloride.

You have to clean those fluxes off after soldering but that shouldn't be
a problem on the wire. Then you'll have a nicely tinned surface to
solder to your aluminum. It should produce a much stronger joint.


Thanks Ed. That sounds like the way to do it. I assume that you mean
that I should use the same tin/zinc solder.


Eh, I should have put in a caveat. I don't know that solder. I've used
some tin-zinc solder on aluminum, but not on steel.

Since yours is the 85/15, rather than 60/40, my guess is that it will
work. Maybe they'd both work. You'll have to try it. I don't think the
acid flux should be a problem with that stuff, but, again, you'll have
to try it.

BTW, if you want to make zinc chloride flux at home, get some muriatic
acid at Home Depot, take an old (or new) carbon-zinc battery apart,
clean the outer (zinc) can, cut it up with tin snips, and toss it in
(one C-cell's worth of zinc, say) with maybe two ounces of muriatic
(dilute hydrochloric) acid. Let stand for a few days. Use.


I took another look at the music wire just now, and it looks like I
didn't have the thing tinned along the whole length that was in the hole
-- improving on "plenty good enough" sounds plenty good to me!


Tinning is my secret weapon for soldering. I think that every copper
joint in my house is now pre-tinned inside and out. It was worth it. I
had leaks in the very old copper joints in my hydronic heating system
when I moved it, but I tinned and re-sweated them all 30 years ago,
and there hasn't been a leak since.

It also improved my school shop projects in junior high school. I
didn't tell the teacher that I was pre-tinning everything before
sweating the joints. My tin cups didn't leak and my candy dishes
stayed together. d8-)

--
Ed Huntress