Yes, JB Weld is a catalyzed epoxy chemically formulated to survive high temperatures and provide good adhesion and shear strength on metal to metal bonds. The aluminum powder thrown in to make it "look like a weld" is a marketing gimmick, but that doesn't mean the base epoxy isn't effective. The lap tensile shear strength of a properly prepared bond is over 1000 psi, with about 1800 psi adhesion. Admittedly not as good as the 30,000 psi you'll get from brazing, but still mighty useful for a lot of applications.