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The in-situ TiB2 particle reinforced aluminum matrix composites are materials that are difficult to machine,owing to hard ceramic particles in the matrix.In the milling process,the polycrystalline diamond (PCD) tools are used for machining these materials instead of carbide cutting tools,which significantly increase the machining cost.In this study,ultrasonic vibration method was applied for milling in-situ TiB2/7050Al metal matrix composites using a TiAlN coated carbide end milling tool.To completely understand the tool wear mechanism in ultrasonic-vibration assisted milling (UAM),the relative motion of the cutting tool and interaction of workpiecetool-chip contact interface was analyzed in detail.Additionally,a comparative experimental study with and without ultrasonic vibration was carried out to investigate the influences of ultrasonic vibration and cutting parameters on the cutting force,tool life and tool wear mechanism.The results show that the motion of the cutting tool relative to the chip changes periodically in the helical direction and the separation of tool and chip occurs in the transverse direction in one vibration period,in ultrasonic vibration assisted cutting.Large instantaneous acceleration can be obtained in axial ultrasonic vibration milling.The cutting force in axial direction is significantly reduced by 42％-57％,40％-57％ and 44％-54％,at different cutting speeds,feed rates and cutting depths,respectively,compared with that in conventional milling.Additionally,the tool life is prolonged approximately 2-5 times when the ultrasonic vibration method is applied.The tool wear patte microcracks are only found in UAM.These might be of great importance for future research in order to understand the cutting mechanisms in UAM of in-situ TiB2/7050Al metal matrix composites.