Polarization curve of galvanically-coupled aluminum and copper specimen in 5 mass%NaCl solution was measured. Polarization resistance curves were obtained by differentiating the experimental polarization curve and have been applied to estimate corrosion rate in the environment above. The aluminum electrode was suffered from pitting attack which shows electrochemical characteristic of fast corrosion system. The corrosion rate of 0.017 mA cm−² which has been calculated by differential polarization curve was in good agreement with that of current density which has been obtained from the results such as corrosion mass loss measurement and electric charge transferred.

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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.

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Friction stir lap welding of 3003 aluminum alloy to both polycarbonate and ABS resin are investigated. The welding was implemented using a numerically controlled friction stir welder using a special FSW tool with a sub probe. Friction stir lap welding of 3003 aluminum alloy to both types of resin materials is possible at higher welding speed than metals. The macrostructures of the joints show anchored structure in which the aluminum alloy partly penetrates into the resin. Maximum tensile shear load of the joint under the welding condition of rotational speed of 1400 rpm and welding speed of 10 mm/s with 3003 aluminum alloy to polycarbonate resin shows 1275 N, and that of the joint under the welding condition of rotational speed of 1100 rpm and welding speed of 14 mm/s with 3003 aluminum alloy to ABS resin shows 834 N. They are higher values than those of the adhesive joints with the same combination.

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In Al–Mg–Si alloys, the negative effect for the artificial age-hardenability occurs by the cluster (1) formation during natural aging following solution treatment and the positive effect occurs by the cluster (2) formation. For the purpose of obtaining information on the constituent elements of these clusters, soft X-ray absorption fine structure (XAFS) measurements of Mg–K edge and Si–K edge were carried out with the liquid nitrogen cooling. From radial structure function calculated from the extended X-ray absorption fine structure (EXAFS) spectra, since average nearest neighbor distance from Mg atom or Si atom decreases by the formation of cluster (1), it is considered that cluster (1) contains both Mg and Si atoms. The absorption edge energy of Si–K shifted to higher energy by the formation of cluster (1). This indicates that the Si valence increased and ion binding property is high for the bonding with neighbor atoms of Si atom in cluster (1). Since the binding force of ionic bond is stronger than that of a metallic bond, cluster (1) is difficult to be decomposed in the artificial aging and the negative effect is shown.

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