I enjoy working with it because it does challenge me.
I've trained many welders to weld aluminum and the same problem comes up time after time, cleaning and keeping everything used to work the aluminum clean.
I would suggest looking into the mechanical properties of the alloy being considered. Elongation as well as the tensile and yield strengths are important. However, due consideration must be given to the type of alloy to be used; heat treatable verus nonheat treatable alloying systems. The alloying elements used can affect weldability. Some of the high strength aluminum alloys, 7075 for example utilizes zinc as it alloying consituant, resulting in a non-weldable alloying system.
Some mechanical properties of alloys such as 6061 degrade in the weld and heat affected zones. Consider the as wrought condition of 6061-T6, the tensile strength is on the order of 42,000 psi. Once it is welded, the materials properties are considered acceptable if the tensile strength is 24,000 psi.
The AWS Welding Handbooks has some good information on aluminum, but my favorite reference is WELDING Kaiser Aluminum. I use the Second Edition published in 1978. Dated, perhaps, but I had a heck of a time tracking down a copy when I found this one a few years ago. Maybe E-bay or Amazon are two possible places to start a search if you're interested.
Here's a few examples of the mechanical properties pulled from my Kaiser reference book:
1100 welded to 1100 aluminum using 4043 filler metal TS - 13,400 psi YS - 6,000 psi Elongation - 21% compared to unwelded 1100-H16 - TS - 19,000, YS - 17,000 Elong. 4%
3003 welded to 3003 aluminum using 4043 filler metal TS - 17,000 psi YS - 8,300 psi Elongation - 19% compared to unwelded 3003-H16 - TS - 24,000, YS - 21,000 Elong. 4%
5050 welded to 5050 alumnium using 4043 filler metal TS - 23,000 psi YS - 12,000 psi Elongation - 16% compared to unwelded 5050-0 - TS - 14,000, YS - 5,000 Elong. 22%
5052 welded to 5052 alumium using 5356 filler metal TS - 30,000 psi YS - 15,000 psi Elongation - 18% compared to unwelded 5052-0 - TS - 25,000, YS - 9500 Elong. 20%
5086 welded to 5086 aluminum using 5183 filler metal TS - 39,000 psi YS - 16,000 psi Elongation - 21% compared to unwelded 5086-0 - TS - 35,000, YS - 14,000 Elong. 18%
6061 welded to 6061 aluminum using 5356 filler metal TS - 30,000 psi YS - 19,000 psi Elongation - 13% compared to unwelded 6061-T6- TS - 30,000, YS - 25,000 Elong. 8%
The values reported by Kaiser are on the high side and are for welds that are "perfect". The values of the welded tensile strength and yield strength seem to be higher than the requirements of AWS B2.1. However, my point being that the mechanical properties of the weld are related to the filler metal used, the welding process (time at temperature for some alloys), the alloying system, and whether the aluminum alloy is heat treatable. It difficult to predict how the mechanical properties with change when the base metal is welded. So, bottom line, you need to have a source of good information and use your references before making you decission on what alloy to use and what filler metal to use. Personnally, I use AWS B2.1 and D1.2 for welded aluminum alloys and I use Kaiser as a starting point when working with aluminum in general. The AWS literature does not always agree with the information published by Kaiser, but that's not entirely unexpected in the wonderfull world of metallurgy.
Nonheat treatable alloys are rolled to increase their strength. Generally, they lose that added strength when welded. Heat treatable alloys are generally precipitation hardened. Welding usually overages the heat treatable alloys and degrades the mechanical properties. But don't bet your house on it unless you know exactly how it is being welded, what filler metal is being used, how it is being cleaned before welding, what post weld heat treatment is going to be performed, etc.
As for bending aluminum tubes, look at the elongation values. Those alloys having low elongation values are going to crack when bent to a small radius. You may have to experiment to find a radius and bending method or equipment that will work for your application. I have to imagine that different bending machines that utilize different mandrels and shoes will produce different results. If your application involves a large number of bends, an investment in equipment is warrented. If you are a job shop with only a few parts to be produced on a short run basis, it may be wise to look at a change in material to accommodate the equipment you have. As for bending plate materials, the formula given in B2.1 for bend testing welded aluminum samples should work for both parent material and welded materials. The formula allows you to use the thickness and elongation values to calculate a bend radius. Theres a lot of variables to consider, more than can be considered in this forum.
Good luck - Al