Actually sunder was a bit wrong when he told you to heat the plate red hot and bend it, aluminum will just discolor a bit when heated and if you use an ox-acet torch shortly after it discolors it will melt into a pile of slag. If you use pop rivets to fasten the corners buy the stainless steel rivets, ordinary steel fasteners react with the aluminum and cause it to oxidise, it kind of rusts. Small carriage bolts might work and not look to bad. Also if you use a grinder make sure you buy wheels rated for aluminum, I,m pretty sure ferrous wheels will just plug up when used on aluminum. There are also various saw blades out there for cutting it.