[Farmwelding]

Try AL without filler once.

Don't worry-tacks without filler I have done a few times and found out real quick why not to. Got an inch into a butt joint and I heard a pop and about half way down it turned into a lap joint. T-joint on aluminum I wouldn't do but if it wasn't critical outside corners some laps and tight butt joints can be done without filler(cue corny sex joke from Jeff)

I'll pass on the corny sex joke but I feel bad for you that you could only "get an inch into a butt joint"...are you Irish?

Well at least I'm not chinese(no offense to those who are) and no I'm Norwegian and Serbian. And I will not discuss the matter any further

[Turbo]

I've only ever heard that it is weaker with aluminum. On steels it depends mostly on the type of joint.