The ultra-precision machinability of SiCp/Al composites is investigated experimentally.A scanning electron microscope (SEM) is used to examine the machined surfaces,chips,chip roots and tool wear lands,and a surface profiling instrument is taken to measure the surface profile roughnesses in different turning conditions.The results show that the machined surface remains a lot of defects such as pits,voids,microcracks,grooves,protuberances,matrix tearing,etc.The tool geometries,cutting speeds,feed rates,particle reinforcement sizes and the volume fractions are the significant influence factors of surface roughness.Generally,a segmental chip is formed in turning composites due to the effect of dynamic microcrack behavior.The tool-workpiece relative vibration and the removal modes of SiC particles are the main mechanisms of surface generation.The microwear,chipping,peeling and the abrasive wear are the main wear patterns by using the Single Crystal Diamond (SCD) tool,while Polycrystalline Diamond (PCD) tool mainly suffers from the abrasive wear on the rake face and the adhesive wear on the flank face.The experimental result indicates that the SiCp/Al composites has a relatively bad machinability.However,when the cutting parameters are rationally chosen,a surface roughness Ra of 24.7 nm can be obtained for SiCp/2024Al(in a volume fraction of 15%).