Capability of infrared thermography for studying the friction stir welding process

The Friction Stir Welding (FSW) is an innovative solid-state welding method based on frictional and stirring phenomena, discovered and patented by TWI Ltd in 1991, providing high quality components for aerospace, marine and automotive industrial fields. In this process, a rotating non-consumable tool that plunges into the work piece and moves forward produces the heat necessary to weld the parts together. The much lower temperatures compared with those achieved in traditional welding processes by melting, determine the following main advantages of FSW: minimal mechanical distortion, excellent surface finish, absence of splash, no crack formation and porosity after welding, thanks to the low input of total heat. This work deals with the use of thermographic techniques for monitoring the friction stir welding process applied on AA 5754-H111 plates, in order to evaluate the quality of the produced joints in terms of presence of defects and Mechanical strength. The adopted experimental approach was addressed to study and optimizing the FSW process by analyzing the thermographic sequences and extracting several indexes related to the heating involved in the process. Such the indexes, the maximum temperature, the heating and cooling rate of the material, correlated to the frictional power input and the presence of defects respectively, have been investigated for different process parameters (the travel and rotation tool speeds) configurations. The results of the research have been quantitatively supported and characterized by destructive and non-destructive techniques.