Milling performance evaluation and cooling/lubrication mechanism of Al-50wt% Si alloy based on various environmentally sustainable manufacturing strategies

Silicon aluminum alloy with Si weight percentage in 50% (Al-50wt% Si) is a typical difficult-to-machine composite. In order to improve its machinability, it is necessary to optimize the friction state at the tool-Si-Al alloy interface by cooling/lubrication. Using appropriate cooling and lubricating media can drive machining operations towards cleaner and more sustainable targets. However, the synergy between Si-Al alloy special material structure, material properties, and multiphase coolants/lubricants is still unknown. In this study, the machining performance of Al-50wt% Si alloy under three milling environments (MEs), namely, dry, supercritical carbon dioxide (scCO2), supercritical carbon dioxide–based minimum quantity lubrication (scCO2-MQL), was discussed. The theoretical analysis was made to understand the scCO2-MQL permeation mechanism. The effects of various cutting parameters and MEs on cutting force, cutting temperature, surface roughness, and surface morphology were investigated. The results show that the lowest cutting force and temperature can be found in scCO2-MQL ME owing to its excellent cooling/lubrication and heat transfer performance. The scCO2-MQL coolant/lubricant can inhibit the spalling and crushing of Si particles. Therefore, the lowest surface roughness which is reduced by 32.34% compared with dry milling and the best surface morphology can be obtained in scCO2-MQL milling. An interaction model between tool cutting edge-Si particles in scCO2/scCO2-MQL MEs has also been presented. The results indicate that the performance of scCO2-MQL as a clean and sustainable cooling/lubrication technique can result in an appreciable improvement in milling Al-50wt% Si alloy.