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This paper describes a butt-welding of AZ31B magnesium alloy plate to commercially pure titanium (CPTi) plate by the solid state welding using a rotating probe with a thread, The effect of the right-hand and left-hand thread on the tensile strength and microstructure was investigated. The following results were obtained in this study. The probe with a thread increased the tensile strength of a joint by about 79％ or less compared with without a thread. There were little differences in the maximum tensile strength of the joints made by the right-hand thread and the left-hand thread. Using the probe without a thread, the fragments of CPTi were produced in a continuous form, but using the probe with a thread. the fine fragments of CPTi tended to scatter in Mg alloy matrix. The increase in the tensile strength of the joints using the probe with a thread was considered to be due to the sufficient plastic flow of Mg alloy caused by the fine fragments of CPTi scattered in Mg alloy matrix. However, the tensile strength of the joint was lower than that of the parent material and the fracture path occurred around the interface. X-ray diffraction analysis revealed a deformation texture with the (002) basal plane near the interface of the magnesium side. It seems that both of the decrease in Al concentration in the Mg alloy and the formation of the deformation texture with the (002) basal plane caused the tensile strength lower, compared with parent material.

We tried to join steel to Al-Mg alloy using a resistance spot welding method. The effect of Mg in Al-Mg alloy on the strength and the interfacial microstructure of the joint was investigated. Additionally, the effect of an insert metal of commercially pure aluminum, which was put into the bonding interface, on the joint strength was investigated. The following results were obtained. The cross tensile strength of a joint between SS400 steel and commercially pure aluminum (SS400/Al) was high and fracture occurred in the aluminum base metal. However, the strength of a joint between SS400 and Al-Mg aluminum alloy was remarkably low and less than 30％ of that of the SS400/Al joint. An intermetallic compound layer developed so thickly at the bonded interface of the SS400/Al-Mg alloy joint that the joint strength decreased. The intermetallic compound layer developed more thickly as Mg content in the Al-Mg alloy increased. Using an insert metal of commercially pure aluminum containing little Mg successfully improved the strength of the SS400/Al-Mg alloy joint and the strength was equivalent to that of the base metal.

Authors tried to butt-weld a mild steel plate to an aluminum alloy plate by the solid slate welding using a rotating pin. This study investigated the effects of a pin rotation speed, the position for the pin axis to be inserted and the pin diameter on the tensile strength and the microstructure of the joint. The main results obtained are as follows: Butt-welding of a steel plate to an aluminum alloy plate was easily and successfully achieved. The maximum tensile strength of the joint was about 86％ of that of the aluminum alloy base metal. Many fragments of the steel were scattered in the aluminum alloy matrix, and fracture tended to occur along the interface between the fragment and the aluminum matrix. A small amount of intermetallic compounds was formed at the upper pan of the steel/aluminum interface, while no intermetallic compounds were observed in the middle and bottom parts of the interface. A little intermetallic compound was also often formed at the interface between the steel fragments and the aluminum matrix. The regions where the intermetallic compounds formed seem to be fracture paths in a joint.

This study was carried out to develop the flux and filler metals that enabled brazing a magnesium alloy plate of AZ31B at the temperature lower than 490℃. The following results were obtained in this study. The newly developed flux that consisted of CaCl2, LiCl and NaCl containing Ca ion and Liion could successfully removed the oxide film from the magnesium alloy surface at around 450℃, and enabled us to braze the magnesium alloy at the temperature lower than 490℃. In addition, we were successful in developing the brazing filler metal with the melting temperature lower than 480℃ that consisted of magnesium and indium as a main component and a small amount of zinc to lower the melting temperature. A joint with high strength equivalent to the base metal one was achieved using the above flux and the filler metal with little zinc, and the joint strength decreased with the increase in the zinc content.

This study was carried out to clarify whether it is possible or not to improve the mechanical properties of welds by means of applying ultrasonic vibration to the weld metal. Autogenous weld by TIG process was made on an austenitic stainless steel plate vibrated ultrasonically. The effects of the ultrasonic vibration on the solidification structure and the mechanical properties of the weld were examined. The main results obtained in this study are as follows. The ultrasonic vibration applied to the weld metal makes the tensile strength of the weld higher than that of the conventional weld. By the ultrasonic vibration, the width of an austenite columnar crystal in the weld metal is decreased and this is likely to be one of the factors to increase the tensile strength of the weld. The ultrasonic vibration changes the microstructure in the weld metal from cellular dendrite morphology in non-vibrated weld metal to subgrain morphology aligned in the growth direction. The existence of the subgrain boundary is also likely to be one of the factors to increase the tensile strength of the weld. The ultrasonic vibration decreased the primary dendrite arm spacing in the weld metal, causing the weld strength to increase. The larger the ultrasonic vibration amplitude is, the more conspicuous the above phenomena are.