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Microstructures and mechanical properties of dissimilar welding joint between Al alloy and Mg alloy by Friction Stir Welding (FSW) were investigated in comparison with laser welding of the same combination. Dissimilar joint of Al and Mg alloy by laser welding was very brittle because of building up Mg 17 Al 12 inter metallic compounds in fusion zone. On the other hand, FSW is anticipated to welding dissimilar alloys with enough joint strength because it is a solid-state process without melting. In this paper, FSW was carried out to make dissimilar butt joints of Al alloy and AZ31 magnesium alloy with various tool rotational speed and welding speed. These joints showed higher hardness in their stir zones than that of parent AZ31 alloy because of Mg-Al inter metallic compound formation. However, the hardness of stir zone was lower than that of fusion zone of laser welding, and was changed with the welding parameters of tool rotational speed and welding speed (i.e. heat input ratio of FSW). The optimum welding conditions of Mg and Al dissimilar FSW joint and the influence of inter metallic compound distribution with mixing of materials in stir zone were discussed.

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The cathodic reaction of Ti has been studied in a CaF 2 -MgF 2 bath with CaO and TiO 2 at 1373K. Cyclic voltammograms were measured in the baths of various compositions, and the dependence of the cathodic reaction of Ti on the bath composition was discussed. With reference to the results of the cyclic voltammetry, Ti metal deposition by potentio-static electrolysis was attempted. It was shown that the reduction sequence of Ti consisted of three steps, and Ti metal was deposited under the suitable condition. The cathodic behavior of Ti was influenced by the molar ratio of TiO 2 to CaO in the melt. Considering the previous results of Ti electrolysis by using DC-ESR unit, it is strongly suggested that a binuclear complex ion of Ti with O, such as Ti 2 O 7