Acoustic Softening and Hardening of Aluminum in High-Frequency Vibration-Assisted Micro/Meso Forming

Abstract

A hybrid micro/meso forming assisted by high-frequency vibration was experimentally investigated by upsetting aluminum. Experiments with various vibration amplitudes and durations were conducted. The high-frequency vibration resulted in both acoustic softening and hardening behavior. Results showed that the overall forming stress reduced by 30% when a transverse vibration of 9.3 kHz was applied, but the stress recovered once the vibration stopped. On the other hand, a hardening behavior was observed during the vibration and resulted in a permanent hardening of the material even after the vibration had stopped. The effects of acoustic softening and hardening were coupled during the vibration-assisted upsetting. It was found that larger vibration amplitude led to a more significant acoustic softening and hardening. The findings of this study provided a basis to understand the underlying mechanisms of vibration-assisted forming.

Keywords:

• Aluminum
• Compression
• Hardening
• Metal forming
• Micromanufacturing
• Softening
• Stresses
• Vibration

ACKNOWLEDGMENTS

The authors greatly appreciate the financial support from the United States National Science Foundation (CMMI-0800353). We also acknowledge the support from National Natural Science Foundation of China (Grant No. 50930005, 50775203), Zhejiang Provincial Natural Science Foundation of China (Grant No. Z1090373), and China Scholarship Council for the opportunity of the international collaborative research. Finally, the authors would like to thank the valuable discussion with Julie Slaughter (ETREMA Products, Inc.) and Zhihua Wang (Iowa state university).