how to join 2 mm aluminium plate

[tamingsari]

im building a speaker type solar cooker using aluminium plate and i don't know the best way to join them i've tried to weld them with TRG GAS but it's really hard to do and i don't know how to join them together

 

[freckle]

tamingsari,
It is difficult to weld aluminium. You need an inert gas environment to do any electric welding. This should be done by a specialist in TIG/MIG welding.
Another way of connecting 2 plates of aluminium are bonding (maybe you need a special type if the temeperature gets too high) or riveting.
Using rivets is probably the easiest way.
Hope this was helpful,
Jelto