study of hardness and impact resistance effect in Friction Stir Welding process with Bobbin tool in Aluminum 6061-T6 alloy

In this research the effect of different rotational speeds and different chosen materials for producing the Bobbin tool in friction stir welding process on hardness and impact resistance alterations for Aluminum 6061-T6 alloy is being studied. According to the results, the most desirable tool to accomplish this process should be from H13 hot-work steel and the pin length should be as long as the work piece thickness. The most optimized ratio between tool shoulders diameter and pin length is about 3 to 5. Accordingly, the designed tool for the mentioned process had 20 mm shoulder diameter, 6 mm pin diameter and 4 mm pin length. Results showed that increasing the rotational speed had desirable effect on connections outward quality and also cause raising the amount of consumed energy for breaking the work pieces and naturally it decreases the return angle of the projectile. Microstructure hardness tests showed that welding speed increasing caused welded zone grains size changing. So it will increase the weld hardness. Furthermore, joints macrostructure’s defects studied and determined that increasing rotational speed has good effect in decreasing these defects. Also in this research, the effect of using HSS tool steel as the bobbin tool material checked that despite better results in hardness tests in same speeds in compared with H13 hot-work steel, finally H13 chose as the bobbin tool material due to the better strength in most other speeds. 1500 rpms selected as the best rotational speed in terms of affect on mechanical properties.