The problem with soldering to aluminum is that the aluminum oxidixes before
it gets hot enough for the solder to stick. The trick is to puddle the
solder on the aluminum, them using a stanless brush or something the solder
won't stick to, brush the aluminum under the hot solder. That way the air
can't get ot it to oxidize it. The solder will tin it and stick fine. I have
been doing this since 1948.