Joining of Dissimilar Materials through a Novel Hybrid Friction Stir Resistance Spot Welding Process

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A reliable, efficient, and economical method for joining dissimilar materials is highly desired in many industrial applications (e.g., automotive, aerospace, and defense industries). Such a method enables utilization of multi-material structures and reduction of vehicle weight. Achievement of reliable dissimilar material joints will provide design guidance for future multi-material vehicle structures. This award supports fundamental research to provide knowledge needed to create a novel, hybrid, and highly efficient joining method that integrates traditional resistance spot welding method with recently developed friction stir process. Research results can greatly contribute to the vehicle light-weighting efforts and thus to increased fuel economy of transportation vehicles and future sustainability.The objectives of this research are: (1) to determine the effects of pulsed electric currents on the thermal and mechanical stress fields, and material behaviors when joining dissimilar materials through the use of electro-plastically enhanced friction stir spot welding, and (2) to create the mathematical relationship between key input parameters (e.g., pulsed electric current magnitude and frequency, rotational speed of friction stir tool, plunge speed, etc.) and the resulting prediction of process dynamics and the associated process performance metrics such as joint quality, temperature distribution, and welding force and torque. The scope of this research includes the modeling and analysis of material flow stress and morphology in the welding zone where dissimilar materials are fused through the friction stir technique in resistance spot welding process. A multi-physics modeling approach will be utilized to calculate the material, temperature and stress distribution fields. This model will also be utilized to analyze the effects of electro-plasticity and heating associated with pulsed electric current on material behavior in the weld nuggets. Multiple phase flow theories will be used for describing dissimilar material behaviors in the weld nugget. In order to quantify the joint quality, both mechanical tests and microstructure analysis will be conducted.