Evaluation of local strain distribution in ultrasonic enhanced Al 6061-T6 friction stir weld nugget by EBSD analysis

Abstract Representative strain states in Al 6061-T6 friction stir weld nuggets prepared with and without ultrasonic vibration were evaluated using strain component data from electron backscattered diffraction analysis. Strain components of various weld nugget locations in final grain structures and approximate strain components of the similar locations at a pseudo-intermediate grain size were accessed by varying average grain size of locations during data processing. Net strain components at the pseudo-intermediate states were higher than those at the final grain structure. Variations in net strain components at each location were analyzed to elucidate grain structure evolution with and without the ultrasonic effect. Results revealed that strain component distributions varied from location to location. Net strain component at center location increased with depth while it decreased towards weld nugget extremities. The net strain components are slightly higher in the presence of ultrasonic vibrations. Relative effect of ultrasonic energy on grain structure evolution is interpreted based on specific strain component (SSC). In the presence of ultrasonic vibrations, SSC is high which causes higher strain dependent grain refinement and recrystallization is most affected by strain. When SSC is low, additional factors control recrystallization. Position of ultrasonic factor reflects the ultrasonic effect.