Development and assessment of a new single-use tool for joining Ti-6Al-4V by friction stir welding
TWI Core Research Project 1140/2020
Friction stir welding (FSW) is now a well-established process for joining light alloys. The relatively low temperature (~500°C) required to soften and plasticise aluminium alloys allows the use of steel based FSW tools, a material which is readily available, low-cost and has a good welding life.
However, tool materials and designs for welding higher temperature alloys such as titanium present a significant challenge, because not only must they be able to withstand high welding forces and torque levels, they must also operate at high temperatures of typically 1000-1200°C. Refractory metals, such as tungsten and molybdenum, are the current preferred materials, but there is only very limited use reported by industry. These have historically provided a FSW tool with properties capable of making welds, however, the cost of the material, producing the tool features and the weld life put a very large burden on the commercial viability of FSW in all but very high value applications. Therefore, a lower cost tooling system could make FSW more financially accessible to a wide range of industries.
To develop and assess a low-cost, single-use, tooling system based on silicon nitride for welding high strength titanium alloys, particularly focusing on Ti-6Al-4V.