Last year we used Bosch extruded alum. for the bottom part of our chassis and then used 1" and 1.5" alum. Angle for the rest of the structure and we only has one little bend when a clamping bot grabbed us and we tried to pull free.
When we built our chassis we cut the pieces to length then bolted them together. Then once we liked how it was set up we started replacing the hardware with welded joints. We never had our extruded alum. welds break but we did have some of the welds for the angle break. I think the person that did the welding touched and wasn't exactly sure what he was doing. If you touch the tungsten electrode from a TIG welder to the metal you are welding then it contaminates the tip and the welds you make after you touch become very brittle if you don't grind out the part where you touched and break off the end of the electrode and start again.
Welding anything is as strong or stronger then the parent metal that you are joining. So it's definitely better then bolting. If you weld it together then you can save up to five pounds of fasteners.
For those people that want a fractional sized extrusion may I recommend you go to
80-20 extruded aluminum they have fractional and metric extrusion that is practically identical to the Bosch extrusion.