Modelling of the heat-affected and thermomechanically affected zones in a Ti-6Al-4V inertia friction weld

Inertia friction welding has been used across the aerospace, automotive and power-generation industries for the fabrication of complex axi-symmetric components for over forty years. The process sees one axi-symmetric piece held stationary and another piece brought in to contact set to rotate about its axis of symmetry by a flywheel with the system under an applied load across the joint. Plasticization at the joint interface through the frictional heating sees the two pieces bond together. The titanium alloy Ti-6Al-4V has been widely studied for inertia welding applications. A successful selection of processing parameters (flywheel energy and mass, applied load) allows an inertia welding process which produces a very high-integrity weld, with a minimal heat-affected zone (HAZ) and thermo-mechanically affected zone (TMAZ), formed as a narrow band at the interface and extending away in to the material. The width of this narrow band of heated material is dependent upon the process parameters used. A series of experimental inertia friction welds were performed using Ti-6Al-4V, and a finite element modelling framework was developed using the FE code Deform in order to predict the widths of the HAZ and TMAZ at the weld interface. The experimentally observed HAZ boundaries were correlated with the thermal fields from the FE model, whilst TMAZ boundaries were correlated with the Von Mises plastic strain fields.