Effect of Mn Modification on the Tribological Properties of In Situ Al-15Mg2Si Composites Containing Fe as an Impurity

The effect of Mn modification on the tribological properties of Al-15M(2)Si-(0.5-2)Fe composites was investigated. The sliding wear tests were conducted under the applied pressures of 0.25, 0.5, and 1.0MPa at the constant sliding speed of 0.13 m/s. According to the results, the behavior of FeMn-rich intermetallics against the strains induced by sliding wear has an important role in the wear behavior of composites. In low-Fe composites (0.5-1 wt % Fe), Mn promotes the formation of Chinese script alpha-Al-15(Fe,Mn)(3)Si-2 phases instead of harmful beta-Al5FeSi platelets. The formation of these compounds strengthens the substrate and decreases its microcracking tendency giving rise to a more stable tribolayer and improved wear properties. At the higher Fe contents, Mn modification leads to the formation of primary polyhedral or star-like alpha-Al-15(Fe,Mn)(3)Si-2 compounds in the microstructure and substantially neutralizes the harmful effect of the primary beta-Fe crystals on the wear behavior. However, when subjected to the friction-induced surface plastic strains, the near-surface alpha-FeMn particles fracture and incorporate into the tribolayer making it unstable and less protective. The tribolayer stability in Mn-modified composites decreases the chance of adhesion between contacting surfaces, and, under low applied pressures, lowers the average friction coefficient (AFC) and its fluctuation. At higher applied pressures, however, the nonmodified composites exhibit lower AFC, which is probably due to the negative impact of beta-Fe fragments on the tribolayer shear strength.