The effect of the welding tool shape in dissimilar friction stir welding of steel and aluminum on the formation mechanism of the intermetallic compound was investigated. It was found that the heat input during FSW process could be controlled by the tool shape. In addition, the tool shape caused a difference in the IMC formation behavior near the shoulder, which was correlated with the amount of plastic deformation of steel. Arrhenius plots of the IMC formation behavior in various joining processes indicated that the rate constant increased with the strain rate of iron during the reaction process.

6000 series aluminum alloys are used in a variety of fields including architectural products and automobiles. These products require complex cross-sectional shapes and high productivity. In the forming of products that meet these market requirements, surface defects such as pick-up and tearing occur. In the previous report, we focused on the mechanism of pick-up defects on the extrusion surface. The cause of the pick-up defects was the preferential adhe-sion of Mg and O to the die bearing surface. In this paper, a die coating is applied as a method to suppress the pick-up defects. AlCrN, TiAlN, Diamond-like carbon (DLC) were applied and compared to the Nitriding. The number of pick-up in the DLC increased as the stroke progressed, and surface layer delamination of DLC was observed after extrusion. Mg oxide wasn't observed in AlCrN and TiAlN on the bearing surface. And, surface delamination wasn't observed with these coatings. The coatings such as AlCrN and TiAlN to the die bearing surface were effective in suppressing pick-up defects.

Porous aluminum is a multifunctional metal material with a light weight and high energy absorption. In our previous study, it was shown that press forming during the foaming of a precursor can form porous aluminum while maintaining its porous structure. In this study, the jointing of porous aluminum by press forming during the foaming of multiple precursors was investigated. The precursors were fabricated via the friction stir welding route. The joint-ing and shaping of porous aluminum were simultaneously carried out by press forming of the precursors with main-taining their porous structures. From a four-point bending test of the obtained samples, the joint strength was found to be equivalent to the strength of the base porous aluminum. No oxide films were observed at the fracture surfaces generated at the surface of the precursors, which prevented jointing between multiple porous aluminum while po-rous structures were obtained, which indicated good jointing.

Microstructure at the boundary between 5052Al and zirconium foils subjected to friction stir diffusion bonding (FSDB) was examined by transmission electron microscopy (TEM). 5052Al and zirconium foils were welded by travelling of a rotating tool with microindention only into the 5052Al foil. The welding strength of the specimens was higher than the fracture strength of the 5052Al foil. An amorphous layer with a thickness of 2 to 100 nm was found at the welded boundary by edge-on TEM observation. An amorphous phase at a welded boundary has been also reported for other dissimilar metal welding, e.g. aluminum and iron alloys, which exhibits high welding strength. Microstructural evolution at the welded boundary is discussed for dissimilar welding of 5052Al and zirco-nium.