Performance of nanolubricants containing MoS2 nanotubes during form tapping of zinc-coated automotive components

Abstract

The paper presents the first use of nanolubricants containing MoS2 nanotubes for form tapping of zinc-coated steel. MoS2 nanotubes are known for their superb low frictional, anti-wear and extreme pressure properties and have shown a promising performance as nanolubricant additive in many machining and forming applications. However their interfacial interaction with zinc-coated components commonly used in automotive applications and their synergisms and antagonisms with currently used additives in forming oils are two crucial aspects that have not been addressed so far. The assessment of these synergies is of uttermost importance for developing future nanofluid minimum quantity lubrication formulations, since despite their extraordinary performance, MoS2 nanotubes are not able to fulfil all the roles expected from a forming oil. To this end, this paper aims to investigate the performance of MoS2-based nanolubricants in combination with representative forming oil additives. The threads are perform using a form tapping unit with customized data acquisition on zinc-coated steel, as a representative part in automotive applications. The performance of the nanolubricants is thoroughly investigated using advanced analytic methods with the aim of revealing the underlying interface interaction mechanisms for the observed torque behaviour and resulting thread morphology and sub-surface hardness. The results show that MoS2 nanotubes are able to interact and form a tribofilm in Zn coated surfaces that leads to a superb friction performance. In combination with oil additives, MoS2 based nanolubricants have a particularly positive synergy with extreme pressure additives in terms of friction reduction, sub-surface hardening and thread morphology. On contrary, the lowest synergy is achieved in the presence of dispersants, leading to higher torques during form tapping and higher sub-surface hardness in the formed threads.