Aluminum Welding Issue

[scottguehne]

I may be putting this in the wrong area, but here goes anyway.

I am building a solar car chassis at school for my senior design project. We are using aluminum for the frame members. It is 1/8" wall, 1" diam. The joints weld well, or so they appear. We did some destructive testing and found that the welds are failing pretty easily.





We did a destructive test of 4130. This piece behaved as predicted. Weld held, material failed in the HAZ.



If anybody has any input on the aluminum issue, I'd love to hear it. It looks like the base metals are melting, they just aren't joining. The base material also appears to not be mixing well with the filler. Material is supposedly 6061, filler rod is 4043. Welder is a Lincoln Precision Tig 275. Using straight argon. The aluminum weld shown was done at 100 amps, slow travel speed. Joint preparation consisted of cleaning the surfaces with a 3m clean and strip wheel and beveling the joint edges around 45 degrees. The bevel was taken all the way down to the i.d. of the tubes.