Abstract: Friction stir welding(FSW) was performed for TU1 oxygen-free copper sheet with 4mm thickness to investigate the influences of welding parameters on the weld formation, microstructure, mechanical properties and electrical conductivity. It is shown that the butt weld with a smooth surface and no internal defects can be obtained in the range of 300-1 000 r/min rotational speeds and 60-200 mm/min welding travel speeds. The appearance dimension of the joint can be accurately controlled and there is basically no residual welding deformation. The weld zone is mainly composed of the Stirring zone(SZ), the heat affect zone(HAZ) and the base material(BM). There is no thermal mechanical affected zone(TMAZ) observed. The grain sizes have obvious differences in the SZ and HAZ under the condition of 300 r/min, and the differences in grain sizes between SZ and HAZ are gradually reduced with the increase of rotational speed. The same grain sizes can be obtained approximately among SZ, HAZ and BM under the condition of 800 r/min, and variation of welding speed has a small influence on the difference of grain size between SZ and HAZ. The hardness distribution in the weld zone is uneven, the obvious soften zone is produced in the SZ and HAZ when the rotational speed is greater than 600 r/min, and the HAZ has the lowest hardness. The conductivity of SZ is better than that of BM, while the conductivity of HAZ is lower than that of BM, and the average conductivity in the weld is in the range of 99.5%-102.5 %IACS. When the welding parameters are 300 r/min-60 mm/min, the tensile strength of the welded joint is more than 90% of the base metal, and the elongation is more than14.5%. The fracture mode presents excellent ductile fracture characteristics.

Key words: TU1 copper, friction stir welding, microstructure features, mechanical properties, electrical conductivity