- 1mm ali box? no it won't be strong enough
- If you are trying to weld the same box chances are you are blowing holes in it as the current you are using is too high. I have never heard of ali being welded with an arc welder. Can you provide some details on the rods you are using? Ali is a nightmare to weld at the best of times so I'm not overly surprised.
- brackets with nuts and bolts or use some steel box section. Bit heavier however far easier to weld.