Graduate School of Engineering
Department of Materials Processing

Interface Science and Engineering of Joining (Prof. Sato, Asst. Prof. Tokita)

Research Topics

Control of weld interface during dissimilar welding

Welding of dissimilar materials is an important process to manufacture the future structures and devices, but it is hard to produce the high-performance welds because thick intermetallic compound layer, which deteriorates the weld properties, is generally formed at the weld interface through the excessive reaction during conventional welding processes. Since thickness reduction of the intermetallic compound layer improves the weld properties, many researchers on the dissimilar welding attempt to reduce the thickness of the intermetallic compound layer using low heat-input or solid-state welding processes, but drastic improvement of the weld properties is still difficult. On the other hand, the interfacial reaction during dissimilar welding should be chemically controlled, but the chemical effects on interfacial reaction and weld properties have hardly been clarified. In our group, development of new dissimilar welding process to create the new interface with the aimed properties has been attempted through design and control of interfacial reaction as well as usage of solid state welding processes.

Microstructural studies on friction stir welding

Friction stir welding (FSW) has been widely used in various industrial fields, such as construction of external fuel tank of rockets, rolling stock of railways, high speed vessels, bridges, etc. Many research attempts to expand the practical applications of FSW more, but understanding of the mechanisms and phenomena of FSW is still lacking. Our group is examining the FSW mechanisms and phenomena based on metallurgical aspects in various metallic materials, such as aluminum alloys, magnesium alloys, copper, steels and titanium alloys, to provide fundamental knowledge to enhance the weld quality and reliability. Moreover, development of tool materials for steels and titanium alloys, feasibility of dissimilar welding, and modification of microstructure and properties using friction stir processing are also examined in our group.

Interfacial phenomena in ultrasonic welding of thin metals

Ultrasonic welding (USW) is a solid state process which can produce a joint between thin metallic materials through ultrasonic vibrating energy and normal clamping force. The USW technique is characterized by a lower energy input, shorter welding time and thinner workpieces than the other welding techniques. Thus, USW technique has a great deal of potential as an environmentally-friendly and cost-effective tool in many industrial fields. However, there is currently little academic understanding on the ultrasonic welding mechanisms despite the engineering significance and past research efforts. Our works on USW technique aim to understand the welding mechanisms based on systematic examinations of the microstructural evolution and mechanical properties of the ultrasonic welds.

Fig. 1:Friction stir welding tool made of Co-based alloy for high-softening-temperature materials.

Fig. 1:
Friction stir welding tool made of Co-based alloy for high-softening-temperature materials.

Fig. 2:Microstructural characterization of ultrasonic welds in dissimilar metals

Fig. 2:
Microstructural characterization of ultrasonic welds in dissimilar metals