Cold plasma and different nano-lubricants multi-energy field coupling-assisted micro-milling of Al-Li alloy 2195-T8 and flow rate optimization

Al-Li alloy has been widely adopted in the aerospace field because of its high specific strength, low density, superior low-temperature properties, good corrosion resistance, and excellent superplastic forming properties. However, the good plasticity of Al-Li alloy causes the material to adhere to tools, decreasing surface quality and tool life. Multi-energy field coupling of cold plasma (CP) and nano-lubricant minimum quantity lubrication (NMQL) may solve this problem, in which the selection and flow rate optimization of the nano-lubricant are of great importance. Micro-milling experiments were carried out using this assisted method, which was characterized by micro-milling force, micro-morphology, 3D surface morphology, tool wear, and surface roughness (Sa). The mechanism was revealed by contact angle test, transmission electron microscope (TEM), nano-scratch experiment, X-ray photoelectron spectroscopy (XPS), nanoindentation test, and friction coefficient characterization. Results indicated that CP could improve the wettability of different nano-lubricants on the workpiece surface and enhance the removal rate of Al-Li alloy. A comparison of different nano-lubricants revealed that the Al2O3nano-lubricant showed excellent performance in reducing micro-milling force, tool wear, and Sa. In addition, when coupling CP and Al2O3nano-lubricant for micro-milling Al-Li alloy, a surface with Sa value of 13 nm could be obtained, which was 59.4 % and 31.6 % lower than that of dry and Al2O3nano-lubricant, respectively. Finally, the usage of the Al2O3nano-lubricant was optimized to 6–7.5 mL/h under the guarantee of machined surface quality.