Microstructures and wear property of surfaces on plasma nitrided AC4C and AC9B aluminum alloys

AC4C (Al–7%Si) and AC9B (Al–20%Si) aluminum alloys have been nitrided by means of the electron-beam-excited-plasma (EBEP) technique to improve surface properties. The specimens have been characterized with respect to the following properties: wear resistance, phase identification (X-ray diffraction) , surface and cross-sectional microstructures. The friction coefficient of nitrided AC4C decreased from 0.6 for an un-nitrided AC4C alloy to 0.12 and that of nitrided AC9B decreased to 0.15. Both of the two kinds of alloys nitrided by EBEP technique formed relatively uniformly AlN layer. In the AlN layer produced both on AC4C alloy and on AC9B alloy, the dendritic-shaped grains were formed perpendicular to the surface with different orientations. Si3N4 was formed not only at the Al/AlN interface but also in the AlN layer. It contributes to the adhesion properties and wear resistance of the AlN layer to the substrate.