On Sat, 30 Jun 2012 21:15:57 -0400, wrote:

On Sat, 30 Jun 2012 09:10:21 -0700, wrote:

On Fri, 29 Jun 2012 19:15:13 -0700 (PDT), George Herold
wrote:

On Jun 29, 3:47*pm, Stanley Schaefer wrote:
On Jun 29, 6:48*am, George Herold wrote:

(reposted from SED)
I want to try soldering some aluminum plate (0.032”) onto each side
of
a brass cylinder. *When trying to solder aluminum in the past I
failed. *I think I heard that some Al alloys are easier to solder
than
others. *I’ve got a choice (From McMaster-C) of 6061, 2024. 7075, and
1100. * Any idea of which is better?

I was also planning on getting some aluminum flux and some Zn/tin
solder from McM-C. *Other suggestions welcome.

Thanks

George H.

It IS possible, but you have to use something to scratch through the
oxide coat first to bare aluminum. *Usual practice is to puddle the
solder on the aluminum and use a stainless brush through the molten
solder until the surface is tinned, then sweat the other piece to it.

Yeah, I figured I'd tin both sides and then mash 'em together..
(not sure exactly how to do the mashing, from center out at least.)

I never thought (or heard) of brushing it while under the solder,
Thanks!
My Alcoa book suggests that the high zinc-content solders work the
best, another one recommends almost pure tin, go figure. *Fluxes
usually have some really active content to dissolve the aluminum oxide
and will result in severe corrosion if not removed/neutralized.

Yeah.. been there with some SS fluxes. Should be fine if I can tin it
all nicely.


If there's significant stress and it's a butt joint, you may have
cracking and joint failure. *In that case you might need some
redesign, like going to solder tabs on your plates and maybe a thin
aluminum shrink-fit tube over your brass to solder to.

Well if solder doesn't work, then maybe some Al 'loaded' epoxy will,
'be the ticket'.


Stan

Thanks again Stan,

George H.
Greetings George,
What Stan says about scratching the surface through the solder is
right on. You can solder without any flux at all. I have used the
aluminum solders available at the hardware store and the strength is
remarkable. You can buy little stainless brushes that are about the
size of a toothbrush at the hardware store too. Once the surface is
tinned it is easy to solder to anything else. If it was me I would
avoid the use of flux on the aluminum just for ease of cleaning. Once
the solder is molten and you start scratching the aluminum through the
solder you will see that the solder will follow the brush as the
brush moves beyond the area initially covered with solder.
Eric
Another trick is to sand the aluminum clean and OIL it, then solder.
Vegatable oil, kerosine, WD-40, or motor oil will all work. do the
final cleaning/sandong/wire-brushing through the oil and it can't
oxidize so the solder tins the aluminum very easily. After it is
tinned you can solder anything to it.
I tried for the first time recently some tinning flux for plumbing.
This is the flux that has the finely ground nonleaded silver bearing
solder mixed with the flux. It worked very well for a non plumbing job
soldering manganese bronze. I'm gonna try it today on aluminum with
the wire brush trick, like the oil trick above. I'll post the results
here.
Eric