The most common methods of joining metals together are soldering and welding. In some cases, though, these methods may not be practical and you may need to look for quicker, easier methods of gluing aluminum to itself or other materials. Though there are many types of craft and construction glues on the market, only a few are well suited for metal bonding in terms of strength and capable of joining non-porous surfaces. While not suitable for large-scale construction projects, metal glues are suitable for small aluminum crafts and fittings.
Epoxy is sometimes known as "casting resin"; though the two are marketed and sold for different purposes, they are essentially the same. Epoxy resin is a hard plastic that's made through the mixture of two chemicals into a thick liquid. The liquid hardens, creating a firm, thick bond between whatever items it's touching. This makes epoxy one of the few glues that's good for joining hard, heavy, non-porous materals like metal, glass and stone. Sheet aluminum, being relatively lightweight for a sheet metal, will easily join with a heavy-duty epoxy, provided the liquid resin is applied in high enough quantities for the project.
Liquid weld, also known as cold weld, is actually a glue, but it's intended to join together metals and has a metallic look, imitating the look of a soldered or welded joint. Liquid weld is a type of two-part resin that's specially designed for heavy-duty metal joint uses. Leading brands of cold weld are made to withstand not only heavy amounts of pressure on the joints themselves but high extremes of heat and cold. This type of product is sold in forms ranging from thin glues to thick, moldable putty glues that you can shape like clay. Liquid welding glues are designed for heavy-duty metal gluing, making them the best choice for large-scale metal gluing projects.
Cyanoacrylate is the generic term for the heavy-duty glue that's sold under the brand names Crazy Glue and Super Glue™ or sold as jewelry glue. Cyanoacrylate glue provides a hold that's strongly adhesive but weakly cohesive, meaning that the glue has very little body of its own and works best for joining two flat objects. This glue is best for gluing very small pieces of flat aluminum or gluing small pieces of other material to aluminum.
With thin, lightweight aluminum, you can glue the metal using hot glue, provided that the metal has a few holes drilled in it through which the melted glue can flow, then harden. On its own, the hot glue will not provide a very strong hold, but used with holes in this manner, it creates a mechanical bond strong enough to support the weight of the metal. This type of joint is ideal for temporary projects, such as theater set decorations, because you can easily peel the glue away to disassemble later. You can also use this technique to join the metal with silicone glue, which has similar properties to hot glue but does not require the use of a heat gun.