Mechanical properties and microstructure evolution of T2 copper in multimodal ultrasonic vibration assisted micro-compression

Abstract

Multimodal ultrasonic vibration (UV) assisted micro-forming has been widely investigated for its advantages of further reducing forming loads and improving forming quality. However, the influence mechanism of different UV modes on microstructure evolution and mechanical properties was still unclear. Multimodal UV assisted micro-compression tests on T2 copper with different grains and sample sizes were conducted in this study. The microstructure evolution for different UV modes was observed by EBSD. The results showed that the true stress reduction caused by UV was increased sequentially with tool ultrasonic vibration (TV), mold ultrasonic vibration (MV) and compound ultrasonic vibration (CV). The region of grain deformation was shifted along the direction of UV, and the MV promoted the uniform distribution of deformation stress. The grain refinement, fiber streamline density, grain deformation and rotation degree were further enhanced under CV, due to the synergistic effect of TV and MV. Additionally, a coupled theoretical model considering both acoustic softening effect and size effect was proposed for describing the mechanical properties. And a physical model of dislocation motion in different UV modes was developed for describing the microstructure evolution. The maximum error between the theoretical and experimental results was only 2.39%. This study provides a theoretical basis for the optimization of UV assisted micro-forming process.