Kazuyoshi Katoh

Tensile properties of 6061-T6 friction stir welds and constitutive modelling in transverse and longitudinal orientations

Abstract Tensile stress–strain properties of Al alloy 6061-T6 (AA6061-T6) and its butt welds produced by the friction stir welding (FSW) process were characterized in two different loading orientations. AA6061-T6 FS welds were made under three sets of welding conditions. Micro-hardness tests were performed to investigate microstructural evolution during the FSW process. Flat tensile specimens were machined normal and parallel to the weld line. Transvers and longitudinal tensile tests were run on the base material (AA6061-T6) and its FS welds in an Instron testing machine. The strength and ductility (or fracture strain) of the FS welds observed in the transverse orientation were substantially less than those in the longitudinal orientation. Constitutive modelling of uniaxial tensile stress–strain behaviour in both orientations was presented using a rate-independent Ludwik equation. In addition, microstructures of the base material and its FS welds were examined with optical and transmission electron microscopy to discuss the decrease in the flow stress level and the increase in the strain hardening rate of the FS welds.

Effects of friction welding conditions on the mechanical properties of friction welded joints in 7075 aluminium alloy

Summary Friction welding was carried out under various welding conditions using high strength 7075 aluminium alloy; an investigation into the structure and the mechanical properties of joints thus obtained leads to the following conclusions: The fibrous structure at the heat affected zone changed to align in the direction of flash expulsion and the fibrous structure at the weld zone disappeared and a non-directional fine grain structure was evident. The hardness at the weld interface had a lower value than that of the base metal and an even more softened zone than the weld interface was noted at the heat affected zone. The hardness values at the weld interface and the softened zone were seen to recover after friction welding due to natural ageing but did not recover fully. Both the values of the tensile strength and the elongation declined compared with the base metal in joints made under the conditions that gave the maximum value of tensile strength; the former was 81% and the latter was 83% that of the ...

Some characteristics of friction welded joints between particulate alumina composite material and 6061 aluminium alloy

Summary Friction welded joints were made with 6061 aluminium alloy and aluminium alloy composite material (MMC) containing 16.1% vol. dispersed particulate alumina and the structures and mechanical properties of these joints were examined. For a short friction time the heat affected zone of a joint was formed almost parallel to the weld interface; however, with increasing friction time it became shaped like a concave lens such that the centre was thin and the outer circumference was thick. The hardness of the weld interface showed a lower value than that of both base materials and the softened zone was observed on both the MMC and the 6061 alloy side. The tensile strength of such a joint was 75% of that of the MMC base material and the maximum elongation value was 60% of that of the MMC. The fracture position after joint tensile testing was, in either case, at the heat affected zone in the vicinity of the weld interface on the MMC side. The joint impact values achieved were similar to or greater than that...