Should preheating be required to fillet weld half inch thick aluminum?

[lpfullmetal]

Hey there guys. I got a question i want to throw out your way. So i need to fillet weld a 4"x.5" aluminum flat bar to another 4"X.5" flat bar. The alloy is 6061t and my filler is 1/16th 5356. Ill be using a miller aluma pro with a miller deltaweld. Now the question...should i preheat this or can i just weld. The peices are about 19 feet in length. So there you go..if you need more information about this project let me know.

[eecervantes83]

Bevel both sides
tack ends
Clampon a flat surface
preheat 200-300f
Weld.
Flip clamp.
weld .

[MMW]

I would pre-heat the beginning so you don't get a cold start. Once you are burning wire you should be fine.

[Portable Welder]

Eecervantes 83 is probably given a better pre heat temp since its only 1/2" thick, I was preheating to 400 degrees because my blocks of aliminum that I was welding were 7" thick x 2' wide x 5' long and would pull the heat away from my weld zone extremely fast.