As soon as the material turns shiney its ready
to lay the rod into it.. all I use on alum is
100% argon.. I've been doing alum for a long
time.. I enjoy doing alum.. yes a good SS brush
helps alot
EDIT
Also lean the tip of the torch to the heavier/thicker
material that will give you a better jump(jump is
the point where the second material or filler rod
joins as one.. at that time the heat is much more
consistent
Also on your tungsten.. dont grind it to a point
loke you do on the MIG.. use a piece of bronze and
flip the machine to reverse then hold the tip
vertical and hit the pedal for a moment.. this will
give your tip a nice round point(the current will run
around in a circle which heats much nicer and that
will make for a easier jump for the rod)