Aluminum gas welding rod comes in two varieties, bare and flux-cored. Bare is recommended for brazing thin sheets, extruded shapes and especially corner joints. Flux-cored has non-corrosive, non-hygroscopic flux inside a tubular rod; no separate flux required. It's used for joining light gauge aluminum used in furniture, truck and trailer bodies, window frames, and aircraft instruments with excellent color match but will darken if anodized. Both are very fluid with a capillary action similar to silver brazing alloys.

Gas Welding Rods Product Guide