Unsymmetric rod to plate rotary friction welding of dissimilar martensitic stainless steel and low carbon steel for automotive applications–mathematical modeling and optimization

In this investigation, dissimilar rod to plate joints of AISI 431 martensitic stainless steel (MSS) and AISI 1018 low carbon steel (LCS) are developed using rotary friction welding (RFW) for automotive applications. RFW being a solid-state welding (SSW) process is employed to avoid the problems in fusion welding of dissimilar materials and unsymmetrical joint configuration particularly solidification cracking, wider heat affected zone (HAZ), evolution of detrimental phases and distortion. The RFW parameters specifically friction pressure/friction time (FRNP/FRNT), forging pressure/forging time (FRGP/FRGT) and rotational speed (RTSP) were optimized using response surface methodology (RSM) to maximize tensile strength (TS) and weld interface hardness (WIH) of MSS/LCS rod to plate joints. The parametric mathematical models (PMMs) were developed to predict TS and WIH of MSS/LCS rod to plate joints. The 3D response surfaces were developed using PMMs which show the optimum conditions of RFW parameters for obtaining greater TS and WIH of MSS/LCS rod to plate joints. The direct and interaction effect of RFW parameters on performance characteristics of rod to plate joints was analyzed from 3D response surfaces. The microstructural characteristics of MSS/LCS rod to plate joints developed using optimized parameters were analyzed using optical microscopy. The phase analysis of joint interface was studied using X-ray diffraction (XRD) analysis. Results showed that the MSS/LCS rod to plate joints developed using FRNP/FRNT of 7.14 MPa/s, FRGP/FRGT of 7.14 MPa/s and RTSP of 26.66 rps exhibited greater TS and WIH of 650 MPa and 515 HV 0.5 respectively. The greater TS and WIH of dissimilar MSS/LCS rod to plate joints is attributed to the evolution of finer acicular martensitic structure in weld zone and narrower HAZ.