From Suppliersonline.com which is a guide for metal suppliers and purchasers, welding of 6013 aluminum says:

The preferred methods of welding are TIG or MIG using AL 4043 filler rod for general purposes. For higher strength weldments the filler metal should be AL 4643 and in heavy section weldments (over 1/2") post-weld solution heat treating and aging is recommended.

In order to weld any sort of aluminum well, one must clean the surface with a scuffing pad and a chemical cleaner to remove impurities and oxides which inhibit a good weld. Preheating the metal is recommended since heating provides a better cooling profile for the weld afterwards to prevent cracking.

In the lab, the welding of 6013 was quite hard for a beginner since welding aluminum is usually one of the harder metals to learn how to weld on. But as the weld pool forms, the arc must be moved quicker through the piece to avoid a melt through due to aluminum’s high conductivity. It is pretty tricky to learn how to weld aluminum, since the oxide layer prevents any viewing of the weld pool as it forms, and the fact that aluminum does not glow makes the pool harder to spot.

Welding filler was not used in the lab in order to obtain better samples for testing purposes.

After the weld was created, heat treating is necessary since it reduces the stress concentrations and reduces cracking.