Effects of tool geometry and welding rates on the tool wear behavior and shape optimization in friction stir welding of aluminum alloy 6061 + 20% aluminum oxide MMC
FSW is a new solid-state process currently being investigated for joining aluminum alloys that are difficult to weld, where there is no perceptible wear of the pin tool throughout the experiment. The present report investigates and examines tool wear in the friction-stir welding of Al 6061-T6 and Al 6061-T6 containing 20% (volume) Al2O3 particles, a metal matrix composite (MMC), in order to compare wear optimized tool geometries and corresponding parameters. The weld tool, referred to as pin tool or nib, did not exhibit any measurable wear in the FSW of the 6061 Al alloy even after traversing tens of meters of material. However, the pin tool geometry changed during the FSW of the Al 6061-T6 containing 20% (volume) Al2O3 particles. Tool wear was measured in relation to the original tool by weighing the photograph of the tool and comparing the percentage change relative to the original tool photograph. The maximum wear rate was roughly 0.64 %/cm at 1000 rpm for the MMC at 1 mm/s traverse speed. The best performance involving the least wear for MMC FSW was observed at a tool rotational speed of 500 rpm and a traverse speed of 3 mm/s; where the corresponding wear rate was 0.13 %/cm. Optical, scanning and transmission microscopy were used to characterize the microstructures of the base material and weld zone for the MMC confirming the solid phase nature of the technique. The microstructure of the friction stir weld zone shows a characteristic dynamic recrystallization phenomenon that acts as a mechanism to accommodate the super-plastic deformation and facilitates the bonding. Rockwell E hardness profiles for both aluminum alloys were measured from the base metals through the FSW zone near the through-thickness mid-section. In the FSW of Al 6061 containing 20% (volume) Al2O3 particles, tool wear has been shown to depend primarily on rotational and traverse speeds, with optimum wear occurring at 1000 rpm. However, as the traverse or actual weld speed is increased from 1 mm/s to 11 mm/s, tool wear and tool wear rate decline. The most significant part of this work was the emergence of a self-optimized tool shape after a considerable traverse distance. When these shapes are developed, tool wear becomes negligible and final shape influences the residual weld properties by variations in the residual through-weld hardness profiles at the start of welding process in contrast to the end of welding experiments. A weld-related flow phenomenon in connection with the specific tool geometry during the FSW of MMC samples was observed using various right-hand threaded pin tools and self-optimized tool shape pins. It may be concluded from this study that using a pin with self-optimized shape and no threads can be used successfully to join Al2O 3 reinforced aluminum alloys. As a result, the self-optimizing wear phenomena may provide a basis for designing optimized tools for other FSW systems, especially those involving appreciable tool wear or any other applications for which wear resistance is important. (Abstract shortened by UMI.)
Prado, Rafael Arcangel, "Effects of tool geometry and welding rates on the tool wear behavior and shape optimization in friction stir welding of aluminum alloy 6061 + 20% aluminum oxide MMC" (2005). ETD Collection for University of Texas, El Paso. AAI3196413.