||In this study, 20 mm thick pure copper plates were friction stir welded (FSW) by three different tool materials at tilt angle of 1.5°, tool rotating speed of 1000 rpm, and different feed speeds to investigate the effect of tool material and pin geometry on the pin deformation. In the FSW experiments, the downward force and the temperature were measured to record their time histories. Finally, effects of feed speed on the downward force, the temperature and the joint strength were investigated. The mechanical properties of the weld were discussed by observing the metallography of the fractured surface in the tensile test after welding.|
Experimental results show that the temperature achieved 870°C after dwell time of 10 seconds in the friction stir spot welding using three tool materials. The high-speed steel tool was obviously deformed after welding, and it was not suitable as a tool material. Inconel 600 and Nimonic 75 were selected as the materials with the tool reusability. The pin with the angle of 40° was easy to deform during FSW process due to less material at its tip. Moreover, the material at the bottom of the workpiece was not fully driven, resulting in insufficient backfilling of the material with void defects. Consequently, the pin with the angle of 30° was selected.
Results showed that the tensile strength of the weld had no obvious variation under the feed speeds of 45~86 mm/min after FSW process. The top of workpieces could achieve more than 90% of tensile strength of pure copper, and the elongation could achieve more than 75% of base metal. Since stirring was less uneven at the bottom of workpieces, it had more than 80% of tensile strength, and the elongation could achieve more than 40% of base metal. In addition, the faster the feed speed, the slighter the hardness of the workpiece, due to the finer the grain in the stirring zone by observing the metallography of the weld.