Joining different grades of low carbon steel to develop unsymmetrical rod to plate joints using rotary friction welding for automotive applications

Abstract

The main objective of this investigation is to optimize the rotary friction welding (RFW) parameters for maximizing the tensile strength (TS) and weld interface hardness (WIH) of rod to plate joints of different grades of low carbon steel and analyze the effect of RFW parameters on TS and WIH of joints. AISI 1018 and AISI 1020 grades of low carbon steel are joined to develop unsymmetrical rod to plate joint using RFW for automotive applications. RFW being a solid-state welding (SSW) was employed to avoid the problems in fusion welding and development of unsymmetrical joints such as solidification cracking, wider heat affected zone (HAZ) and distortion. The RFW parameters specifically friction pressure/friction time (FRNP/FNRT), forging pressure/forging time (FRGP/FRGT) and rotational speed (rps) were optimized using response surface methodology (RSM) to maximize the strength and hardness of rod to plate joints. The three factor – five level central composite design (3 × 5 - CCD) consisting of less experiments was employed for designing experimental matrix. The tensile strength and microhardness tests were performed to evaluate mechanical performance of rod to plate joints. The numerical and graphical optimization techniques of RSM were employed to optimize the RFW parameters. The 3D response surfaces were developed which show the optimum conditions of RFW parameters. The effect of RFW parameters on TS and WIH of rod to plate joints was analyzed from 3D response surfaces. The microstructural features of optimized rod to plate joint were analyzed using optical microscopy. The fractured surfaces of rod to plate joints were analyzed using scanning electron microscopy. Results showed that rod to plate joints developed using FRNP/FRNT of 3.71 MPa/s, FRGP/FRGT of 3.71 MPa/s and RTSP of 19.99 rps exhibited higher TS and WIH of 452 MPa and 252 HV0.5 respectively. The higher TS and WIH of rod to plate joints is attributed to the evolution of finer grain structure in weld zone and narrower HAZ. The RTSP revealed greater effect on TS and WIH of rod to plate joints followed by FRGP/FRGT and FRNP/FRNT.