The study of the effect of parameters of the mode of copper friction stir welding on the mechanical properties and electrical conductivity of welded joints

Copper is widely used when producing current-conducting parts, basically the electrotechnical power equipment buses. Traditional ways of welding copper become complicated because of high thermal conductivity, fluidity, significant oxidation at fusing temperature, and susceptibility. The application of the solid-phase welding methods, a prominent representative of which is friction stir welding (FSW), is one of the ways to solve problems when welding copper. The paper presents the experimental study of the influence of a tool working part shape and the welding mode parameters: welding rate, tool rotation frequency, and tool dip angle – on the possibility of the appearance of defects in welded joints of M1 copper plates of 5 mm in thickness produced by FSW. The paper contains the results of mechanical tests on static tension and bending of welded joints with a tunnel defect and without it. Welded joints with a tunnel defect showed a decrease in mechanical properties level: the value of ultimate tensile strength at stretching is lower by 33 %, and the specific elongation is lower by 8 % than ones of a joint without defects. The authors specify some factors influencing the appearance of defects at FSW: the welding rate, tool rotation frequency, tool working part construction, tool dip angle, strength and depth of immersion, pin displacement, blank thickness, and grip conditions. The study identified that the application of a tool with a concave surface taper shoulder allows producing welded joints without external and internal defects. Based on data obtained during the experimental research, the authors determined the welding modes, which makes it possible to produce welded joints with the electrical resistance value at the level of a parent metal: tool rotation frequency is 1250 rpm, welding rate is 25 mm/min, and tool immersion depth is no less than 0.41 mm.