Microstructure Evolution and Surface Performance of the Rolled 5B70 Aluminum Alloy Processed via Ultrasonic Impact Treatment

The main purpose of this work was to study the microstructure evolution and surface properties of rolled 5B70 aluminum alloy during ultrasonic impact treatment (UIT). The microstructural features of the surface deformed layer were characterized by OM and EBSD. The result indicated that UIT could transform the linear microstructure to a plastic flow feature and the deformation evolution characteristics of lamellar size gradient (LSG), which is characterized by gradient deformation from the grain boundary to the interior in the linear structure of each layer. The newly formed fine grains and the refined long gradient structure were formed due to the continuous dynamic recrystallization (CDRX), which is caused by the high strains. Surface roughness and hardness were consistent with the variation trend of geometrically necessary dislocations (GND) density. When the UIT coverage reaches 400%, the surface roughness performs best, and the UIT surface hardness is about 53.9 MPa higher than the base material.