Tool assisted friction welding: A FSW related technique for the linear lap welding of very thin steel plates

A Friction Stir Welding (FSW) related technique, which will be labelled Tool Assisted Friction Welding (TAFW), is presented in the current paper. Using this technique, linear lap welding of very thin steel plates is obtained by using a non-consumable columnar tool, with a featureless shoulder, to generate heat by friction with the components to be welded, as in FSW, and also to promote the joining of the plates, under pressure, as in Friction Welding (FW). The joining mechanisms, as well as the thermomechanical conditions developed during welding, will be discussed based on the metallurgical analysis of similar welds produced in two steels: a galvanised low carbon steel (DX51D) and a mild steel (DC01). Mechanical testing, using Digital Image Correlation (DIC) for strain data acquisition, enabled to assess welds strength and plastic properties. The results obtained prove that the TAFW technique enables to obtain very good quality welds, for both base materials, at a very high welding speed and low tool wear/damage. An important influence of the galvanised coating of the DX51D steel on the welding conditions and weld microstructure was also observed.