Investigation of Induction Heating Process for Selective Melting of Aluminum Alloy for the Repair of Exit Hole Defect in Friction Stir Welding Process

The pursuit of an effective exit hole closure method for preparing high-quality welds has gained significant attention in the research community, driven by the potential of friction stir welding in space and aircraft manufacturing. Many techniques have been developed for avoiding the defect, but no effective solution has yet been observed. In this study, the potential of induction heating was investigated as an alternative method to repair exit holes. The present work aims to find an optimal set of induction heating parameters to effectively fuse a billet of similar volume to an exit hole. A numerical investigation was conducted by developing a two-dimensional (2D) axis-symmetric coupled electromagnetic-thermal model to analyze the effect of induction heating process parameters on the thermal behavior of AA1100 aluminum alloy. Process parameters such as coil geometry, stand-off distance, current and excitation frequency were varied, and the optimal parameters were identified based on temperature distribution, heating rate, thermal stress and phase change in the material. A pancake coil geometry, stand-off distance of 2 mm, current density of 1000 A and frequency of 100 kHz were the optimal set of parameters chosen from the numerical analysis for the effective repair of exit hole. A preliminary experimental investigation was conducted by employing the chosen process parameters and a powder-flux mixture in place of the billet. The observations reveal the possibility of achieving a sound joint under solid-state sintering condition. The use of fine powder-flux mixture at high temperatures facilitated solid-state diffusion resulting in a defect-free interface. The proposed system can be an alternative to the existing processes used for repair with an advantage to act as an in situ repair technique without compromising the original weld properties in the vicinity of the defect. The findings of this study have significant implications for space and aircraft manufacturing, where the use of friction stir welding is prevalent and exit hole defects are a challenge.