Grain growth of Cu wires during Joule heat welding

The Joule heat welding technique requires only current to join fine-scale materials together and is a useful way to create and repair electric circuits. During Joule heat welding, the temperature in the wire system increases, leading to grain growth and affecting the mechanical properties of the welded wires. This paper reports the grain growth of Cu wires during Joule heat welding and the mechanical properties of the welded wires. The diameter of a Cu wire was 25 μm, and the welded wires were subjected to tensile testing. Although the welded wires were broken outside the welds, the yield stress and fracture stress of the welded wires were two-thirds of the yield stress and fracture stress of the as-received Cu wire. The decrease in the yield stress and fracture stress of a Cu wire was due to its grain growth. Tensile testing of Cu wires heat-treated at various temperatures by current was also conducted. The region around the fracture position of the Cu wires was heated to around 900 °C during welding, and the grain there was found to have grown to about twice the size of that before testing.