Study on Surface Characteristics and Work Hardening of SiCp/Al Composites by SCCO2-MQL Combined with Ultrasonic Vibration Milling

This study investigated the milling of SiCp/Al composite materials using Polycrystalline Diamond (PCD) tools under various machining conditions, including dry cutting conditions, supercritical carbon dioxide (SCCO2) conditions, supercritical carbon dioxide cooling with minimum quantity lubrication (SCCO2-MQL) conditions, ultrasonic vibration conditions, and supercritical carbon dioxide cooling with minimum quantity lubrication combined with ultrasonic vibration conditions. The objective was to compare the surface roughness and morphology of the materials under different machining conditions. Furthermore, under dry cutting conditions and SCCO2-MQL combined with ultrasonic vibration, the effects of different milling parameters on the surface roughness and morphology of SiCp/Al composite materials were investigated through a univariate experiment. Microhardness tests were carried out on the machined workpieces to explore the influence of process conditions and milling parameters on work hardening. The experimental results indicate that among all the tested machining conditions, the SCCO2-MQL in combination with the ultrasonic vibration process significantly reduced the surface roughness of the material. When the milling speed was increased from 40 m/min to 120 m/min, both the surface roughness and the degree of work hardening first increased and then decreased. As the feed rate or cutting depth increased, the degree of work hardening also increased. Therefore, under SCCO2-MQL combined with ultrasonic vibration conditions, it is recommended to use a milling speed of more than 60 m/min and avoid using high feed rates and cutting depths in order to optimize the machining performance.