<p>Friction Stir Welding (FSW) is increasingly utilized for copper due to its exceptional thermal and electrical conductivity, which are critical in a variety of industrial applications. However, the FSW of copper presents distinct challenges, primarily attributable to the high thermal conductivity and forces required during the process, which can result in tool wear and compromise weld quality. The objective of this study is to investigate the thermal behavior associated with FSW of copper through the application of different welding pitch using a Coupled Eulerian-Lagrangian (CEL) numerical approach. A three-dimensional finite element model was developed to simulate the process, effectively capturing key parameters such as heat generation, material flow, and temperature distribution within the weld region. The model was validated against experimental data, demonstrating good agreement with a root mean square error (RMSE) of 18.5&#xa0;°C for temperature profiles and 3.2 HV for hardness predictions. The analysis elucidated the effects of welding speed, rotational speed, and tool geometry on heat distribution, peak temperatures, and resultant mechanical properties. The findings provide valuable insights into the optimization of process parameters for enhancing weld quality and extending tool life in copper FSW applications.</p> Graphical Abstract <p></p>