doesn\'t particularly need to be welding but i need to make an air tight permanent seal around 2 very thin sheets of aluminium (like .02 inches thick) i was thinking .02 inch 5052 aluminum because its the thinnest i can find but am obviously up for suggestions.First you need a Tungsten inert gas welder (T.I.G. for short). The second step is to make sure the aluminum is clean. If you just bought it , and it looks clean ; it isn\'t trust me. Steel and aluminum are totally different in a lot of ways and that is one of them. I\'m going to skip the safety instructions and shopping list , under the presumption that you already know the basics. Spray the area to be welded with acetone. rinse with clean water to remove lingering residue. then use a wire brush that has never been used on anything but Aluminum to clean the area. I\'d go with a 4043 welding rod , it\'s a popular choice. Make sure to use clamps so that the 2 pieces of metal are squeezed tightly together with no gaps. (very important) I like to preheat my metal even if it\'s thin sheets , seems to come out better although it isn\'t usually called for in specs. side note ; If you have to step away from your work for more than 8 hours , you\'re going to need to re-prep it since it will have formed a layer of Aluminum oxide by that time.GOOP silicone adhesives are much harder when set than 100% silicone adhesives more commonly seen, but if you are just butting the tubes, epoxy to build a gusset would be a better choice. Always clean all surfaces with soap and water and then with denatured or high percent rubbing (isopropal) alcohol to improve bonding.may not be practical for you but explosive welding is the best way for welding of metal sheets in high performance applications. wave of explosion produce enough heat and pressure to weld sheetsMay be you can use spot welding.But may be that would not give you an air tight permanent seal.So,you can go for Hydraulic pressing as in FERRARI 599 GTO\'s exhaust.(QUITE EXPENSIVE to be done at personal level)TIG okorder.com/Other related question