Tribological evaluation of the Jatropha and Tung-based oils as bio-lubricants on Al-7050-T7451 alloy

Abstract

The search for more sustainable products has motivated the metalworking sector to replace its mineral-based lubricants with renewable products. Vegetable-based oils are renewable resources, more biodegradable, less toxicity and can have a high lubricant potential. Therefore, the vegetable-based oils are a more environmentally friendly alternative to replace the mineral-based oils. The objective of this paper is to evaluate the technical viability of the Tung and Jatropha oils for use in formulation and development of environmentally friendly metalworking fluids (MWFs) for machining processes of Al7050-T7451 alloy. Physical–chemical, tribological (pin-on-disk and reichert tests) and machining analyses were performed to study the technical viability of the vegetable-based oils as a bio-lubricants. The linoleic (C18:2) and linolenic (C18:3) fatty acids of Jatropha oil provide the lubricant film with less resistance to movement between the tribological pair in comparison with Tung oil, leading to lower coefficient of friction (COF). The higher concentration of linolenic fatty acids (C18:3) of Tung oil provides greater resistance to movement, resulting in a higher COF. The unsaturations present in vegetable-based oils carbon chain make it difficult to fill gaps between molecules, reducing metal/metal contact, providing lower wear and better thermo-oxidative stability. Tung emulsion also showed better cooling property, important factor for MWFs. It can be concluded that the vegetable-based oils can be used for formulation and development of environmentally friendly MWFs for the metal-mechanical sector.