Herein, an axial ultrasonic vibration-assisted extrusion cutting (AUV-EC) process was proposed for fabricating ultrafine-grained metal materials, with a mathematical model developed to characterize the cutting motion in this process. Systematic comparative experiments were conducted to evaluate the surface morphology, microstructure, and mechanical properties of chips produced by AUV-EC, extrusion cutting (EC), and free-flow cutting (FC) at varying cutting speeds. Quantitative analysis indicated that under ultrasonic vibration frequencies of 34.5–35 kHz and an amplitude of 8 μm, the linear roughness (Ra) of chips produced via AUV-EC was reduced by 5.4% and 41.1%, respectively, compared with those produced by EC and FC. Meanwhile, the surface roughness (Sa) was correspondingly reduced by 13.6% and 46.9%, respectively, confirming that AUV-EC could significantly improve chip surface quality and mitigate surface roughness. TEM and XRD analyses revealed that the average grain sizes of chips produced by AUV-EC, EC, and FC were 125 nm, 156 nm, and 210 nm, respectively. Thus, AUV-EC could achieve grain refinement. AUV-EC exhibited significantly enhanced dislocation density than the other two methods, presenting a distinct microstructural advantage. These results collectively confirmed that AUV-EC promoted grain refinement by enhancing dislocation entanglement and slip, which facilitated the formation and migration of grain boundaries. Furthermore, the coordinated rearrangement of dislocations drove the development of high-angle grain boundaries, thereby producing ultrafine grains. Vickers hardness and nanoindentation tests demonstrated that AUV-EC-derived chips exhibited higher hardness than EC and FC chips across varying cutting speeds. The H/Er ratio of the AUV-EC sample reached 0.060, representing a 46.3% and 17.7% increase compared to FC and EC counterparts, respectively. This indicated a marked enhancement in the material’s mechanical properties following the introduction of ultrasonic vibration.
