The mechanism of metal transfer was investigated in twist-compression experiments with 6061-T6 aluminum specimens rotating against hardened steel anvils. Mineral oils of 4.5, 30 and 284 mm2/s viscosity at 38 C were used neat and with fatty acids, alcohols, and P and CI EP additives. Even though the initial squeeze films disappeared, sooner with the light oil and later with the heavier oil, the oils limited metal transfer and retransfer and gave a steady-state friction value of 0.2. The heaviest oil maintained a fluid film with a friction value of 0.03 and restricted metal transfer to a thin patchy coating in the valleys of the lapped anvil surface. Some additives limited metal transfer even with the lighter oils. It appeared that stearic acid and stearyl alcohol were effective in reducing friction and metal transfer by forming a boundary film, enhanced in the case of the alcohol by the formation of a gel-like layer. A chlorine-rich aluminum compound formed with chlorinated paraffin.

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