As far as welding is concerned, I would take (or send) it to a Certified AIRCRAFT Welder. They should be able to weld it without any problems and Guarantee the Weld. I've done a fair amount of welding over the years, but when it comes to Aluminum I'll take it to someone that does Aluminum Welding for a living.
Personally, I would just fabricate a new part out of STEEL, it would be much stronger and a lot cheaper than having that broken part welded. JMHO