2015 年 65 巻 9 号 p. 396-402
The mechanism of Flux-free brazing using Al–Si–Mg filler alloys under inert gas atmosphere at ordinary pressure has been investigated. In the wide lap joining test under controlled atmosphere with low oxygen concentration, equal or higher joint rate than CAB (Controlled Atmosphere Brazing) method using fluoride flux was obtained by the addition of 1 mass% or more of Mg in the brazing filler alloy. In the bonding of aluminum, the metallic bond is formed by the destruction of Al2O3 layer of molten brazing filler and base material surface. In the case of stable joining state at joined interface, the oxide layer was broken and fine MgAl2O4 oxide had been dispersed. In the heating process of brazing, the oxide layer was decomposed into MgAl2O4 by Al2O3 layer reacting with Mg in the molten brazing filler. In addition, it was considered that the oxide layer was divided into fine pieces with the flow of the molten brazing filler. On the other hand, as the oxygen concentration in the atmosphere increased, MgO layer on the surface of Al–Si–Mg filler alloy grew thicker. Because MgO layer is not decomposed by Mg at the bonded interface, joining rate decreased significantly.