Plasma-Assisted Hybrid Dissimilar Friction Stir Welding for Joining of DH36 Steel and AISI 1008 Steel: Thermal Modelling and Experimental Analysis

Abstract

Dissimilar materials joining by hybrid FSW involve preheating the harder material ahead of the FSW tool, which reduces the vertical force and improves the weld quality by enhancing the material flow. In this work, both experimental and numerical analyses were conducted for the friction stir welding (FSW) and plasma-assisted friction stir welding (PAFSW) of dissimilar steels such as DH36 shipbuilding steel and AISI 1008 steel. The comparative study was performed on the thermal history, vertical force, mechanical and microstructural characterizations under different welding conditions. The 3D transient thermal phenomenological models were established using Abaqus/CAE 2017 finite element (FE) software package. The moving heat source models for FSW and PAFSW were successfully established, which were embedded in a Fortran code and fed to Abaqus/CAE through DFLUX subroutine. The additional heat source, i.e. plasma arc heat source, was modelled using the Gaussian distribution of heat flux. The stir zone isotherms of the developed numerical models and the transient thermal profiles in the FSW and PAFSW were matched fairly well with experimental results. For the reliable comparative study, the consequence of FSW parameters (i.e. traverse speed and rotational speed) and preheating parameters (i.e. plasma offset and preheating current) on thermal history was investigated. It was observed that the assistance of the plasma preheating ahead of FSW tool was significantly reduced the grain size and vertical force. In contrast, the hardness and the impact toughness values were increased compared to that of FSW.