Most 2xxx series alloys are not considered fusion weldable because of their sensitivity to hot cracking. However, some alloys, such as 2014, 2219 and 2519 are easily welded. The weld metal, of course, will essentially be in the annealed condition. The heat affected zone next to the weld metal will show gradual, localized degradation of the base metal properties. Postweld heat-treatment can be used to restore some or all of the lost strength.

T,

Welcome to the forum!

Here is a nice link from Lincoln electric to go with the good advice posted above. The article focuses on common engineering mistakes (usually poor material selection) in aluminum fabrications. It also lists weldable and non weldable 2XXX series materials.
http://www.lincolnelectric.com/knowledge/articles/content/comistakes.asp

The most common structural choice that you will find in the T6 condition is 2024.

Welds with 2024 usually fail even in ornimental applications.
Do not attempt a load bearing weld unless you have satisfactory engeneering doccumentation stating that what your attempting is actually possible.