Effects of horn type on the microhardness and microstructural homogeneity in ultrasonic-assisted simple shear extrusion

Abstract

The objective of this study was to minimize the friction force within the deformation zone in the simple shear extrusion (SSE) process by utilizing the ultrasonic vibrations directly on pure copper samples. Modal analysis was conducted on two types of horns (cylindrical-exponential-cylindrical and cylindrical-conical-cylindrical) to determine an efficient concentrator. Two punch feed rates of 5 and 10 mm/min, a frequency of 20 kHz, and an amplitude of 15 micrometers were employed in this ultrasonic-assisted simple shear extrusion (USSE) method. The homogeneity of microhardness and microstructure was investigated in both SSE and USSE methods. The findings implied that during the initial pass of the SSE method, the mechanical and microstructural properties were improved by increasing the feed rate; however, no improvement in the microstructural homogeneity was observed in the same pass. In contrast, the USSE process demonstrated enhancements in the mechanical and microstructural properties at a lower feed rate. Furthermore, a significant improvement in the homogeneity of the microhardness and microstructure was reported in USSE due to the uniform distribution of strain under ultrasonic vibrations in the samples. This enhancement was achieved in the first pass of USSE, whereas it occurred in subsequent passes in the SSE method. The cylindrical-exponential-cylindrical horn exhibited a more significant role in improving the homogeneity and mechanical properties compared to the cylindrical-conical-cylindrical horn due to its good concentration and transmission of vibrations.