▎ 摘　　要

This paper studied the effect of graphene additive on the lubricating capacity of vegetable oils. The castor oil, rapeseed oil, and corn oil were chosen as base oils, and ultrasonic agitation was used to prepare the graphene in vegetable oil suspensions with six different mass fractions. These suspensions were utilized as minimum quantity lubrication (MQL) lubricants during the internal tapping process of ADC12 aluminum alloy. Tapping torque and thread surface morphology analyses were applied to evaluate the lubrication performance. The results showed that the pure castor oil MQL achieves the lowest average tapping torque in all the base oils. Meanwhile, the use of graphene additive can significantly reduce the tapping torque, and this torque reduction shows a nonlinear relationship with the graphene mass fraction. As an overall trend, the 0.5% mass fraction is the optimum concentration, which decreased the average torque by 0.64 Nm (11.4%), 1.6 Nm (16.4%), and 1.7 Nm (17.7%) compared with pure castor oil, rapeseed oil, and corn oil, respectively. Moreover, the scratching defects on the thread surface were obviously reduced with the application of graphene additive. This torque-reducing and anti-wear effect could be related with the graphene-related friction films formed on the metal surfaces. The research verified that the vegetable oil-based graphene suspension can be used as a substitute for the conventional mineral oil-based metalworking fluids.