Effect of Different Welding Speeds on Microstructure and Properties of Bobbin Tool Friction Stir Welded Joints of T2 Pure Copper

Based on the successful welding of T2 pure copper with BT-FSW technology, this paper explores the effects of different welding speeds (30, 50, 70 and 90 mm/min) on the microstructure and properties of welded joints at a fixed rotation speed of 1000 rpm. The microstructure, special grain boundary angle distribution, microhardness, tensile properties, electrical conductivity and electrochemical corrosion resistance of the welded joints obtained at different welding speeds were studied and analyzed. The effects of welding speed on the microstructure and properties of T2 pure copper BT-FSW joints were obtained. The results show that the change of welding speed mainly affects the heat input and strain rate during welding. The grain size of WNZ is affected by these two factors, and the grain size of HAZ is mainly affected by the thermal cycle temperature. The WNZ of welded joint obtained under the welding condition of 70 mm/min has the feature of “onion ring”. The proportion of LAGBs and HAGBs does not change significantly with the change of welding speed, while the content of TBs decreases with the increase of welding speed. Under this welding condition, the microhardness value fluctuates greatly, the mechanical properties and electrical conductivity are low, but the electrochemical corrosion resistance is high.