Abstract: A furnace for flux-free soldering of aluminum-containing workpieces in a controlled atmosphere has a furnace chamber through which workpieces to be soldered are made to travel. The furnace chamber itself is a gas-tight metallic muffle which is thermally insulated from the outer part of the furnace and has an inlet for the workpieces and an outlet for them. A first lock chamber is interposed between the furnace chamber and the inlet, and a second lock chamber is interposed between the outlet and the furnace chamber. Arrangements are provided for admitting vacuum and protective gas into the lock chambers, and protective gas into the muffle and a heating arrangement is provided for heating the controlled atmosphere in the muffle.