The composite effect of high-speed ultrasonic vibration milling and pickling post-treatment on Ti-6Al-4V fatigue performance

In aerospace manufacturing, high-speed ultrasonic vibration milling (HUVM) improves the machining accuracy and surface strength of difficult-to-machine alloys. Pickling, a critical post-machining cleaning step for preparing aviation components for spraying and flaw detection, is known to affect surface integrity. This study optimized the technological process by investigating the effects of milling method, ultrasonic vibration assistance, and pickling on the surface integrity and fatigue life of Ti-6Al-4V through experiments and finite element method (FEM) simulations. Results indicated that side milling significantly increased Ti-6Al-4V fatigue life compared to end milling, achieving a 147.8-fold enhancement, attributable to optimized primary surface morphology direction. Pickling also substantially impacted fatigue life. Pickled counterparts subjected to CEM and high-speed ultrasonic vibration end milling (HUVEM) showed fatigue life increases of 23.7 and 44.5 times, respectively, over non-pickled CEM specimens. These improvements resulted from passivation and morphological modifications induced by pickling and ultrasonic vibration assistance. Through characterization of primary and secondary surface geometries and analysis of stress concentration factors, the research elucidated the composite effects of HUVM and pickling on Ti-6Al-4V surface morphology and fatigue performance. These findings provide insights for optimizing Ti-6Al-4V components manufacturing and enhance understanding of the composite mechanisms that extend fatigue life.