[IKE]

Unless you are a pro, assume that the material just outside of the aluminum gets annealed during the welding process. i.e. if you are making a chassis our of 6061 T6 AL, assume strength as annealed 6061. We have had several weld fractures, but they were due to 1 of three issues:

1. Pushing the envelope (we have built a lot of stuff using welded 0.030" AL)
2. Poor joint design (we had 1 failure where afterwards we realised it was a poorly designed joint)
3. Poor welds quality. We have had a weld failure where the weld quality was just plain poor. High inclusion due to carelessness. This didn't make it onto a competition bot.