Study on temperature field, microstructure, and properties of T2 pure copper by bobbin tool friction stir welding.

This paper completes the welding of 4-mm-pure copper with bobbin tool-friction stir welding technology for the first time, and we discovered the evolution of microstructure by combining the temperature field evolution, microstructure, mechanical properties, electrical properties, and chemical corrosion resistance of welded joints. The findings demonstrate that the temperature field is dynamic, with the advancing side experiencing the highest peak temperature (422 °C). The size of recrystallized grain in the stir zone (SZ) is slightly larger than that of the base metal (BM), and the "banded structure" of alternating coarse-grain bands and fine grain bands is observed in this region. The microstructure of the heat-affected zone (HAZ) has larger grain size. Both the advancing and retreating sides of the thermomechanically affected zone (TMAZ) have a distinct microstructure, with the advancing side having a more pronounced elongated and curved microstructure. The welded joint has a specific microstructure gradient from the standpoint of the overall microstructure, which results in the fracture location at TMAZ with the biggest microstructure gradient in the tensile test, and the welded joint's efficiency is only 57.56% of the base metal. At the same time, the resistivity and the chemical corrosion resistance of the welded joint will decrease. During the welding process, the grains in the stir zone mainly undergo geometric dynamic recrystallization and the heat-affected zone mainly undergoes dynamic recovery. [ABSTRACT FROM AUTHOR]