Effect of ultrasonic compound cutting on the microstructure and properties of formed chip

Severe plastic deformation (SPD) with high strain rate can increase the material dislocation density, reduce the grain size, and improve the mechanical properties. In this article, ultrasonic compound cutting (UCC) was proposed to improve the efficiency of preparing ultra-fine grain (UFG) pure copper by SPD methods. The motion characteristics and strain rate model of UCC were analyzed, and it was concluded that the maximum strain rate in the primary shear zone can be increased by ultrasonic vibration. According to the 3D FEM equivalent model of UCC, the UCC and traditional compound cutting (TCC) were compared and analyzed from the perspective of strain rate. The simulation results showed that the strain rate in the shear zone of UCC was significantly larger than that of TCC. The microstructure and mechanical properties of pure copper chip were studied by using a self-developed machining device. The experiment results showed that the grain refinement, dislocation density, and microhardness of pure copper chip were significantly improved in UCC. When the ultrasonic amplitude was 3 μm, the UCC chip grains were about 2.66 μm and the hardness reached 124 HV, which was about 8% higher than the TCC chip. The findings of this research provide an important reference for machining UFG pure copper with enhanced mechanical properties.