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In article ,
says...
In article ,
(Ted Shoemaker) wrote:

Hello,

I have some basic questions about soldering.

Well, first thing is that you don't solder steel or aluminum. Period.

Solder will work just fine on steel. Cleanliness is
important, and a more active flux than you might use for
copper may be helpful, but regular old No-Korode will work
with careful prep. The limiting factor for typical lead/tin
solder will be the solder itself, not the bond.

It's also possible, but not straighforward, to solder
aluminum with Pb/Sn solder. One trick mentioned often on
this NG is to clean and solder under a film of oil to
inhibit the rapid formation of the oxide layer.

You can gob on wads of solder and stick steel or aluminum pieces
together the way you'd stick, for instance, chunks of wood together
using a handful of clay - They'll be joined, yes, but don't count on
*ANYTHING* resembling structural strength, and you'll never get anything
even remotely like a proper solder joint out of the attempt. The metals
just aren't compatible (The solder simply won't "wet" them, so it can't
"grab on" the way you're probaby used to from electronics work) so it's
one of those "ain't gonna happen" things.

Until relatively recently, when lead-bearing solder was either outright
banned, or severely restricted for use in potable water plumbing work,
the main difference between the solders used for plumbing and
electronics work has been the flux - Plumbing uses acid flux,
electronics uses rosin.

Nokorode, perhaps the most widely used plumber's flux for
at least 50 years is zinc chloride and ammonium chloride in
petrolatum (Vaseline). Not an acid flux, but not something
you'd use on a circuit board either.

For the OP, the silver bearing soft soft solders -e.g., All
State 430, Harris Stay Brite (sp?)- are good for decorative
work. They are substantially stronger than lead/tin and
stay shiny with time. Since they do not flow as well as
lead/tin they do require better heat control to get good
results. Also more expensive.

Choice of flux for these solders is similar to lead/tin.
Nokorode is fine for most uses, but there are acid fluxes
that allow soldering stainless steel and other difficult
materials. The acid fluxes (All State Duzall is one) are
trickier to use as they are prone to burning when
overheated, especially a problem with a torch.

Ned Simmons