The tribological behavior of bismuth dithiophosphate as water-based additive in aluminium alloy tapping

Purpose – The purpose of this paper is to study the tribological behavior and mechanism of watersoluble bismuth dithiophosphate as the additive of waterbased cutting fluid in aluminum alloy tapping. Design/methodology/approach – Comparable investigation has been made on the lubrication performance of bismuth dithiophosphate and sodium dithiophosphate in aluminum alloy tapping. The aluminum alloymachined surface finish was observed on scanning electron microscope. The films on the workpiecemachined surface and the tap tool working surface were analyzed by Xray photoelectron spectroscopy. Findings – The results indicated that the water medium containing 1 wt% the prepared watersoluble bismuth dithiophosphate exhibited better tapping efficiency than the liquid paraffin containing 2.5 wt% chlorinated paraffin and 2.5 wt% sulfurized olefin. The bismuth sulfide component in the reaction film on the tap working surface plays a leading role in elevating the tapping efficiency and improving the machined surface finish. Research limitations/implications – The paper is restricted to the lubrication performance of bismuth dithiophosphate as the waterbased cutting fluid additive in 2024 aluminum alloy tapping. Practical implications – The test method adopted is very close to the machined method applied in industry. The test results show that the bismuth dithiophosphate can obviously improve the tapping efficiency and the machined surface finish. Thus, it can be applied to the aluminum alloy cutting in automotive and aviation. Originality/value – An attempt has been made to identify the chemical reaction film sourced from bismuth element and dithiophosphate group on the workpiecemachined surface and the tool working surface and their contribution to enhancing the tapping efficiency and improving the machining surface finish. This is helpful to the designers and the practitioners of the additives of metalworking fluid.