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Surface Chemistry of Aluminium Alloy Slid against Steel Lubricated by Organic Friction Modifier in Hydrocarbon Oil

DOI: 10.1155/2012/926870

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Abstract:

The lubrication mechanism of aluminium alloy slid against steel was investigated from the standpoint of surface chemistry. Low friction and low wear were observed using glycerol mono-olate in a hydrocarbon as lubricant. Increase in the silicon content in the aluminium alloy during rubbing was observed by surface analyses using (1) Auger electron spectroscopy, (2) scanning electron microscopy along with energy dispersive X-ray spectroscopy, and (3) X-ray photoelectron spectroscopy. Mild removal of the passive state (aluminium oxide) from the uppermost surface by the additive during the running-in process was proposed as the lubrication mechanism. The importance of additive chemistry that improves the running-in process was pointed out. 1. Introduction Aluminium-based alloys are lightweight and are expected to be energy saving materials for transportation systems. Aluminium is inherently a soft metal; therefore, it is alloyed with silicon and copper in order that it can have sufficient properties. Several additives for the lubrication of aluminium alloys have been reported [1–6]; however, lubricants that improve the tribological properties of aluminium alloys still need optimisation. Conventional additives for steel do not always improve the tribological properties of aluminium alloys under boundary conditions [7, 8]. These results are attributed to tribo-chemistry related to additives and aluminium surfaces. It should be noted that there are two categories in this chemistry: the first is poor reactivity of the additive with the surface (kinetic issue), and the second is inadequate tribological properties of the boundary film formed on the surface by tribochemical reactions (thermodynamic issue). These problems were studied experimentally by a combination of a well-designed tribotest with surface analysis [8]. Lubricant chemists have to consider these categories while developing an appropriate lubricant for an individual material. Lubrication of aluminium alloys by alcohols is well known [9]. Formation of an amorphous-like boundary film composed of aluminium alkoxide has been detected by chemical analyses [10]. The direct interaction between alcohol and the rubbed aluminium surface has also been analytically detected [11]. Effects of the molecular structure of lubricant on the tribological properties of aluminium alloys are being debated. It has been reported that straight-chain primary alcohols having more than 12 carbons are better lubricants than 1,2-diols [11]. Many researchers have pointed out the importance of bifunctionality in the lubricant

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