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The micro-jet is the main mechanism of cavitation on materials. More and more ultrasonic cavitation assisted machining uses the micro-jet effect in the industrial field. In this paper, the micro-jet impact is considered the micro-cutting process. To deeply analyze the micro-cutting mechanism of micro-jet, the size effect of materials was considered, and the micro-cutting force model of micro-jet was established and solved based on the spherical indentation test theory and the strain gradient plasticity theory. The results showed that the micro-cutting force and impact pressure of micro-jet with size effect are larger than those without size effect and the micro-cutting force of single micro-jet is within 2.35 N. The micro-cutting force of micro-jet increases exponentially with the increase of pit radius, but only slightly increases with the increase of pit depth. When the size effect is considered or not, the impact pressure of micro-jet is 1616–2922 MPa or 1615–1980 MPa, respectively. The increased ratio of micro-cutting force with size effect is 1 + 2 m ¯ 2 a 2 G 2 b h a 2 + h 2 σ JC 2 - 1 × 100 % , which can directly reflect the strength of size effect. The size effect is more obvious when the pit size is smaller, and the maximum increased ratio is 47.54%. The increased ratio increases nonlinearly with the decrease of pit radius and the increase of pit depth. It has a strong correlation with pit radius and pit depth. This paper can provide a theoretical viewpoint and support for the quantitative description of cavitation effect in ultrasonic-assisted machining. [ABSTRACT FROM AUTHOR]

Micro-structure on metal surface can be created with high precision and good surface quality by ultrasonic-assisted electrochemical micromachining (USEMM). One of the prevalent material removal mechanisms in ultrasonic machining (UM) is cavitation erosion. However, the mechanism of material erosion is not clear and worth investigating. This study of the mechanical and chemical effects of the ultrasonic vibration on the 6061 aluminum alloy is targeted to reveal the material processing mechanism in USEMM. Based on the built model, the velocity of micro-jet produced near the workpiece surface by ultrasonic cavitation reaches up to 350 m/s when bubble collapses computed by software MATLAB. The impact of micro-jet produces plastic micro-pits on the metal surface and the convex peak around the edge of the pits, which is verified in ABAQUS software. The metallographic microscope and curves of the electrochemical polarization behavior results indicate a significant grain refinement and a marked increase of anodic dissolution current, as well as a weaker resistance than the original workpiece in NaNO3 electrolyte during UM. The current-time curve during machining demonstrates the passive layer forms on the metal surface and then breaks down at the time of less than 0.0066s in USEMM. Micrographs of scanning electron microscope (SEM) of the machined surface in different stages show that many uniform and flat pits are formed in USEMM, compared with the local uneven pits in EMM. [ABSTRACT FROM AUTHOR]