On the Material Bonding Behaviors in Friction Stir Welding

Abstract

The material bonding defects such as root flaws have been an important kind of welding defects in friction stir welds. In recent years, the growing application of friction stir welding (FSW) in fabricating many critical components, e.g., rocket fuel tank, renewed the need for in-depth understanding for the formation of material bonding defects. This study provides a quantitative investigation to access the material bonding behavior via numerical simulation. It is found that the rapid growth of the bonded fraction is developed owing to the localized thermal-mechanical processing during FSW. The thermal-mechanical condition at the root region is deteriorated greatly as the tool rotation rate decreases. The validity of the simulation results at different welding parameters is confirmed by our microstructural observation. The concepts that we develop open up quantitative prospects for the elimination of defects due to insufficient solid state bonding in FSW and similar material processing approaches.