In-Process Cooling of Friction Stir Extruded Joints for Increased Weld Performance via Compressed Air, Water, Granulated Dry Ice and Liquid Nitrogen
Snyder, Benjamin Anton
This research investigates the effectiveness of various in-process cooling (IPC) sources in the friction stir extrusion (FSE) process to improve the strength and hardness performance of the weld joints. Four cooling sources were used in this research: compressed air, water, granulated dry ice, and liquid nitrogen. Past research has shown that the use of cooling media during the friction stir welding (FSW) process yields stronger welds compared to uncooled welds due to the reduction of post weld microstructural grain growth. The FSE process used in this research is a derivative FSW process that creates a mechanical joint between two metals by extruding the welded material into a preformed material. For this research, the parent material used was aluminum alloy AA6061 T-6 and the grooved material was mild carbon steel. This research also investigates the robustness of the change in performance due to IPC by using multiple FSW parameters which cause various levels of heat generation. The four sets of welding parameters used in this research varied by FSW tool rotational speed (revolution per minute, RPM) and weld traverse speed (inches per minute, IPM). The parameters used were 1500RPM-3IPM, 1500RPM-2IPM, 1000RPM-3IPM, and 1000RPM-2IPM. Rockwell hardness testing and tensile shear testing were then used to evaluate the effectiveness of IPC. The results of this research revealed that IPC FSE joints were stronger and harder than the uncooled joints. Ultimately, the water cooled joints were identified as the most consistent and effective means of increasing FSE joint performance across various welding parameters.