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In this study, the friction stir spot welding (FSSW) of Mg alloy sheets has been tried using an apparatus devised with a CNC milling machine to give the precise control of joining condition including tool speed. The probe tool used is made of hard metal and composed of cylindrical shoulder and pin parts. The variation of morphologies formed after the friction stir spot welding depending on the plunge speed of the tool were investigated at each rpm of tool. The history of the temperature distribution and the vertical load induced during the spot welding with friction time were measured by using an Infrared Thermal Imager (THERMA CAMTM SC2000) and a loadcell located below the specimen fixture, respectively. Tensile-shear tests were also performed to evaluate the fracture load of welded specimens. In order to characterize the friction stir spot welding of Mg alloy sheets, the variation of the fracture load was discussed on micrographic observations, temperature distribution during the FSSW according to the plunge speeds of tool.

A dissimilar friction stir spot welding (FSSW) has been tried using an apparatus which was devised with a CNC milling machine to give a precise control of the friction time and the plunge depth. Variations of the vertical load applied and the temperature history during friction stirring were measured. In this study, the characteristics of dissimilar FSSW of a bulk metallic glass alloy to crystalline metals having lightweight were investigated. Through the investigation of fractographic observation, the EDX analysis and the joining strength, the welding performance of dissimilar FSSW of BMG was evaluated.

The friction welding of three kinds of Zr–Cu–Al bulk glassy alloys (BGAs) which show eutectic or hypoeutectic compositions to similar and dissimilar BGAs and crystalline metals has been tried. The shape and volume of the protrusion formed at the weld interface were investigated. In order to characterize the friction welded interface, micrographic observation and X-ray diffraction analysis on the weld cross-section were carried out. A successful joining of Zr–Cu–Al bulk glassy alloys to similar and dissimilar BGAs was achieved without occurrence of crystallizations at the weld interface through the precise control of friction conditions. In addition, the joining of Zr 50 Cu 40 Al 10 BGA to crystalline alloys was tried, but it was only successful for specific material combinations. The residual strength after welding of dissimilar BGAs was evaluated by the four-point bending test.

The friction welding of Zr-based bulk metallic glass (BMG) rods and tubes to similar BMGs, and to crystalline metals were performed. An infrared thermal imager (FLIR-Thermal Cam SC-2000) was used to measure the temperature distribution at joining interface of the specimens during friction welding. All BMGs adopted in this study showed a successful friction joining to similar BMG. The shape of the protrusion formed at the weld interface were examined. In order to characterize the friction weld interface, the micrographic observation and the X-ray diffraction analysis on the weld cross-section were carried out. The obtained results were discussed based on the temperature distribution measured at the weld interface A successful joining of the BMGs to crystalline metals could be obtained for certain pairs of the material combination through the precise control of the friction condition. The residual strength after dissimilar friction welding of BMG was evaluated by the four-point bending test and compared with the cases of friction welding to similar materials.