Attempt has been made to obtain mullite as a double oxide compound of alumina and silica. Pure and fine mullite particle were prepared by supplying both aluminum acetate as corrosion product of aluminum in anhydride acetic acid solution containing hydrogen peroxide and silica as hydrolysis of tetraethoxysilane. One of new inorganic syntheses named corrosion synthesis is electrochemically explained in the case of making the mullite by applying corrosion phenomena and its product.

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A 2024-T3 aluminum alloy stud with the circular ridge projection at the bottom was welded to a 1.5 mm-thick 5052-H34 aluminum alloy thin plate by the advanced high-speed solid-state joining method. The projection crushed and spread along the plate surface. Joining was achieved within a few milliseconds with a negligible temperature increase of the joint. Asymmetrical deformation occurred on both the inner side and the outer side of the projection. It was found that enlargement of the joining area outside of the projection was effective to increase the joint strength by the present authors' previous study. Based on this guide, in the present study, trial was made to increase the joint strength by determining the optimum projection shape at a bottom of the stud. Three types of projection shape were prepared and they were provided for joining tests at various discharge voltage conditions, and joint interface morphology, joining area and joint strength were compared. When we used the stud with which the projection tip shifted to the inner side, the outer side of the projection spread much wider along the plate surface than the inner side. This worked effectively to increase the joint area of the outside and the resultant joining strength. It is confirmed that the modified projection shape is useful for the stud welding for the thin plate.

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2017-T3 aluminum alloy plates with 0.8 mm thickness were butt welded by friction seam welding using a friction stir welder. Microstructures and mechanical properties of specimens with butt joints using friction seam welding were investigated. Two kinds of welding methods, such as single side pass and double side pass, were applied. Weld interface of both joints was not observed clearly. Weld zone of both joints had finer grain structures than that of the base metal. Hardness of weld zone was softened with 80% of the base metal. The temperature of retreating side of weld zone was higher than that of the advancing side. Tensile strength of single side pass joint showed 93% of the base metal. Tensile strength of double side pass joint was 86% of the base metal.

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