Development of Iridium Tools for Friction Stir Welding (FSW)
Friction stir welding (FSW) is a unique joining method that makes use of the frictional heat generated between the material to be joined and the tool along with the plastic flow of the material being joined which is generated by the stirring action of the tool. FSW offers the advantages of minimal deterioration of joint strength and low deformation after joining, and it has already been commercialized for the joining of aluminum and its alloys in the automotive, railroad rolling stock, and aerospace industries where there is a high reliability is demanded. Although research and development efforts have been going forward toward the use of FSW for iron and steel materials, which represent the majority of metals production, commercialization of the method has been slow. One of the reasons for this is that industry has been unable to find FSW tools that are appropriate for materials having the high melting point and high temperature strength of iron and steel materials. This is where the development of iridium (Ir) materials, which is the specialty of Furuya Metal, comes in.
When iron and steel materials are joined using FSW techniques, the tool is subjected to high temperatures of 1000-1200℃. The oxidation loss and oxides generated by the tool during FSW are the cause of tool erosion. Although most metals having a melting point in excess of 2000℃ are strongly affected by oxygen in the temperature range of 1000-1200℃, with iridium (Ir) there is virtually no oxidation loss or increase due to oxide production and iridium has the greatest resistance to oxidation. Moreover, alloys made with iridium have increased high temperature strength and high temperature hardness, and tools have been developed that support FSW in high temperature materials such as iron and steel. Using iridium alloy tools, FSW has been successfully performed on molybdenum, which has a melting point 1000℃ higher than that of iron, iron and steel materials, titanium and oxide-dispersed reinforced platinum.
- The FSW process
- （1）Two materials to be joined are aligned and clamped.
- （2）A rapidly rotating tool is inserted above the joint surface. (A probe is embedded in the materials being joined.)
- （3）The materials being joined are softened by the frictional heat generated between the tool and the materials being joined, and the rotating tool travels along the length of the joint.
- （4）The softened material flows in the vicinity of the tool due to the stirring action of the tool. The material behind the tool continuously bonds and the two materials being joined are welded together thereby.
- （5）The tool is removed from the materials being joined when the joint has been completed at the predetermined location.