PURPOSE: To produce an Al heat exchanger having excellent corrosion resistance by combining Al members, brazing the members by a potassium fluoroaluminate flux in a non-oxidizing atmosphere and dissolving away the residue of the flux.

CONSTITUTION: The Al or Al alloy members are brazed by using the potassium fluoroaluminate flux in the non-oxidizing atmosphere in the stage of combining said members and integrally joining said members to produce the heat exchanger. The flux or the like essentially consisting of any one kind of KAlF4, K2AlF5, H2O or K3AlF6 or ≥2 kinds thereof is used as the potassium fluoroaluminate flux. The residue of the flux is dissolved away by immersing the joined member in an alkaline soln. such as caustic soda or acidic soln. such as nitric acid or hydrofluoric acid. The surface of the Al or Al alloy member is thereby made conductive and the corrosion resistance of the aluminum heat exchanger is improved.