Material flow promoting effect of the friction stir welding by double spiral tool

For lightweight materials such as aluminum and magnesium alloys, joining technology called "multi-material" technology is required to achieve weight reduction. When joining dissimilar materials in arc welding, there are problems such as the formation of intermetallic compounds. FSW can solve these problems. However, FSW has a problem that defects such as root flow occur due to changes in bonding conditions. In order to suppress defects, it is necessary to optimally control the material flow and to stir the materials to be joined in a coordinated manner, and the shape of the welding tool directly affects this. In this study, we tried to produce a healthy friction stir weld of aluminum and magnesium alloy sheet using a newly designed tool called "double-spiral tool" that can increase the volume of the stir zone around the tool. did. The materials used were A5083 aluminum and AZ31 magnesium alloy sheets with a thickness of 3mm. Two types of tools were used: normal type with M4 to M3 screws (single-spiral tool) and double-spiral type with the same pitch and double lead length. The latter can transport theoretically twice as much metal along the tool axis compared to the former. From this, it can be expected to prevent welding defects by increasing the material flow rate. In this study, we designed and manufactured a "double-spiral tool" with an effect of increasing the material flow rate, and demonstrated that it leads to improved reliability of FSW joints made of dissimilar aluminum and magnesium alloys. It became clear that the double spiral tool effectively enhanced the agitation action and the area of the agitation zone was stacked more densely. The tensile test at room temperature also showed that the double spiral tool has a high merit, that is, high tensile strength.