Study of Plunge Stage for a Hybrid Friction Stir Welding Process Based on Electro-Plastic Effect

In this study, an electrically assisted friction stir welding (FSW) system has been designed and developed. Additional electrodes are assembled and stay in the close proximity of the tool as the tool translates along the weldline. Plunge stage of FSW process has been studied for both aluminum alloy Al 6061 and TRIP 780 steel based on this developed experimental configuration. An effective axial force reduction can be consistently observed after application of a continuous current. In order to compare the relative significance of the associated resistance thermal effect, the workpiece has been preheated to approximately same temperature and it can be shown that around 2/3 of the force reduction can be contributed to the electricity itself. Microstructure of the cross sections for Al 6061 plunge specimens indicated an enhanced dynamic recrystallization process under the influence of current. This phenomenon was not obvious on steel, which is probably due to the higher Joule heating temperature and consequently accelerated grain growth. On the other hand, thermal mechanically affected zone of steel suggested a retarded martensitic phase transformation with electrical current applied.