I agree with jimn
I was taught that the weekest part of the weld is the heat effected zone next to the weld, thats why most fractures are right next to the weld line. "stress is reduced by heat treatment, weld prep design and weld proceedure"
If you look at the original weld it is designed so as not to create a:- direct virtical shear stress line.
p.s. There are also different grades of filler rod /wire with different tensile strenghts so make sure the right one is used
sorry I can't be more helpfull but it's been years since I last welded aluminum.
Paul