That will freaking bend to hell after 1 bunny hop.
I use aluminium. Its light and holds for my riding now. Get something like 2-3 mm thick. Oh and I can give you some other advice since i've made my own bars.
Lets say the inner diameter of the bottom one has to be 10cm big so that it fits the fork right? If your metal is 2mm thick , it will be 102mm for the outer diameter but then the clamp's inner diameter is 104mm. So, put some masking tape and you should be ready to roll.
The measurements are stupid but its just an example.Oh and when you tape the thing right? Its good that the slots are free of tape. Slots = those line things which allows the bars to fit tight onto fork.
I call it slots.