Improving the Tribological Properties of Al-7Fe-5Ni Alloys via Friction Stir Processing

Due to the limited solid-solubility of Fe and Ni in Al, coarse brittle intermetallics rich in Fe and/or Ni are inevitably formed in the as-cast microstructure of Al-Fe-Ni alloys. Upon formation, Fe(Ni)-rich intermetallics significantly deteriorate the properties and restrict the application of alloy in as-cast condition. The purpose of this study was to investigate the effect of friction stir processing (FSP) on microstructure and tribological properties of cast Al-7Fe-5Ni alloy. The dry sliding wear tests were done by using a pin-on-disk type machine under the applied pressures of 1, 2, and 3 MPa, sliding distance of 1000 m, at room temperature. According to the results, FSP (1250 rpm and 8 mm/min) effectively refined the microstructure, especially the coarse primary Al9FeNi intermetallics and eliminated the alloy casting-related defects. FSP also converted the large columnar grains of the cast alloys to the ultrafine equiaxed grains. These microstructural changes enhanced the substrate mechanical properties thereby increased its resistance against sliding-induced plastic flow, leading to the higher tribolayer stability on the surface, and accordingly, higher wear resistance. The results showed that applying 1-pass FSP reduced the wear by 13% and 53% under applied pressures of 1 and 3 MPa, respectively. The friction results also revealed that, compared with the as-cast sample, FSPed samples exhibited lower friction coefficient and friction coefficient fluctuations.