Application of vibration to enhance efficiency of friction stir processing

Friction stir processing (FSP) is a solid-state modification method to process the surface of metals. In this process, due to rotation and traverse motions of a non-consumable tool, metal surface microstructure is refined and its mechanical characteristics are improved. Different methods have been applied to improving the efficiency of FSP. In this research, a new method entitled friction stir vibration processing (FSVP) was presented to enhance the efficiency of FSP. In this method, metal workpiece was vibrated normal to processing line during FSP. Microstructure and mechanical properties including hardness, ultimate tensile strength (UTS) and elongation of A15052 alloy specimens processed using FSP and FSVP methods were analyzed and compared. The results showed that grain size decreased by about 33% as vibration was applied. It was also observed that ultimate tensile strength as well as hardness increased by about 7% as FSVP was applied. This was related to the enhanced straining of metal surface material as vibration was applied. The increase in straining results in the increase of dislocation density. It leads to more development of high angle grain boundaries due to dynamic recrystallization. The results also showed that UTS and elongation of FSV processed specimens increased as vibration frequency increased.