Friction stir welding of titanium alloys

Abstract

The article describes the basic concepts for applying the friction stir welding (FSW) process to components made from titanium alloy. As is well known, titanium and its alloys are demanding applications for FSW due to the high mechanical strength, high melting temperature, low thermal conductivity, susceptibility to atmospheric contamination, and the high tendency for embrittlement of the material due to the absorption of interstitial elements (O, N, and H). Hence, the process parameters have great influence on the microstructure and properties of the welded joint. To date, there is no consolidated experience, even at the international level, on the behaviour of the FSW process for titanium alloys; however, this article reports the main results obtained from recent studies in the field and data provided by the Institute further to tests conducted in relation to research projects aimed at the aeronautics sector. In particular, it is pointed out that the use of conventional tools (consisting of ‘Shoulder Tool’ and ‘Profiled Pin’, both rotating) do not allow the attainment of good quality joints; on the other hand, the use of a novel tool, using a fixed ‘Shoulder Tool’, may represent an important step forward in the development of application of the FSW process to titanium alloys.

Keywords:

• aerospace
• energy input
• friction stir welding
• friction welding
• joint preparation
• mechanical properties
• microstructure
• process conditions
• process equipment
• research and development
• titanium alloys
• weldability