rich brenz wrote:
Thanks Gary,
Here's the real life problem...
After cleaning the Al with a clean wire brush, I apply the flux. I heat
the joint and LONG before the joint has reached the melting temp. of the
solid solder, the flux begins to smoke and turn black forming a nice
hard barrier between the workpiece and the applied solder. As things
currently stand, it seems that I can't help but scorch the flux, to my
chagrin. When all is said and done, I'm left with 2 separate pieces of
nicely scorched Al. BTW, the solder and flux were purchased as a kit.

Rich
You don't say what solder, flux, or type of heat you are using. Some
aluminium solder I've used requires no flux at all. Here in UK its
called Technoweld, but its not really welding. In USA its probable got
another name.
The technique, as others have mentioned, is to first 'tin' the joint by
first scrubbing it with a stainless toothbrush and then scratching it
with a stainless toothpick while applying heat until the solder melts.
It works by mechanically removing the oxide from the material while it
is shielded by the solder. When both parts of the joint have been
tinned, you hold them together and apply heat to melt the solder to make
the joint. You can add more solder as required - once the joint is
tinned it won't oxidise. It works very well, but is no good at all for
'capillary' soldering where the solder runs into small fluxed spaces by
capillary attraction. I suspect this where the name Technoweld comes
from 'cos welding is similar in this respect.

--

Regards, Gary Wooding
(To reply by email, change feet to foot in my address)