Effects of vibration amplitude and relative grain size on the rheological behavior of copper during ultrasonic-assisted microextrusion

Abstract

Ultrasonic-assisted microextrusion tests were performed on pure copper (Cu) with different amplitudes and dimensions to investigate the effects of amplitude and relative grain size L/D (i.e., the ratio of initial grain size L to dimension after extrusion D) on its rheological behavior. The ratio of average extrusion height H to dimension after extrusion D was used as a microformability evaluation parameter. Results showed that the extrusion stress, friction coefficient, and microhardness of Cu decrease with increasing vibration amplitude, whereas its microformability, surface quality, and deformation temperature increase. The effect of relative grain size on microformability could be divided into three sections under different amplitudes. Microformability decreases with increasing L/D when L/D ≤ 0.15 but gradually increases when L/D > 0.35. When 0.15 < L/D ≤ 0.35, experimental repeatability was the poorest and microformability was the worst among the three sections. Moreover, the results of the X-ray diffraction experiment indicated that ultrasonic vibration could effectively promote grain rotation to the (1 1 1) preferred orientation.