Investigations into Microstructure Evolution and Hardening Effect during Ultrasonic Vibration Assisting Hot Compression for High-Strength Aluminum Alloy

Ultrasonic-assisted technology is an efficient method to improve the plasticity of the material. In this paper, ultrasonic vibration was conducted during hot compression test for AA7B04 alloy, and the evolution of microstructure and hardness under different vibration amplitude conditions were discussed in detail through transmission electron microscope (TEM), electron backscattered diffraction (EBSD) and microhardness test. The results show that the specimens under the case of ultrasonic vibration exhibiting the larger size of η´ and η phase when comparing with the ones with only hot compression, indicating the promoting function of nucleation and growth of precipitation. The main recrystallized mechanism is CDRX during ultrasonic vibration assisting hot compression, relying on the climb and slip of dislocations. High fraction of recrystallization were caused by ultrasonic vibration, and the specimens with 5.3 specimen vibration amplitude could reach 61.47%. Besides that, Goss texture were weakened during ultrasonic vibration assisting hot compression. Because of the comprehensive influence of large size of η´ (softening effect) and refined grain size (hardening effect), a slight decreased trend of hardness value is observed for the specimens under ultrasonic vibration assisting hot compression.