Preparation and characterization of carburized layer on pure aluminum by plasma electrolysis

Plasma electrolytic carburizing (PEC) was employed to fabricate a carburized layer on pure aluminum in glycerol electrolyte. The near surface temperature of the aluminum workpiece at different voltages was measured and the electron temperature during cathodic plasma discharge was calculated in terms of optical emission spectroscopy (OES). At 340 V, the temperature of Al workpiece reached 450 °C, but the electron temperature in the discharge envelope fluctuated around 7000 K. The microstructure and phase constituents of the carburized layer were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Its tribological property was measured by a ball-on-disc friction and wear tester under dry sliding against GCr15 steel ball. The corrosion behaviors were evaluated by electrochemical methods and scanning electrochemical microscopy (SECM). It was found that the depth of carburized layer was about 2 μm and its hardness was two times higher than that of the Al substrate. Besides, the friction coefficient of carburized layer containing Al4C3 phase decreased to 0.55, while that of the Al substrate is 0.95. The corrosion current density and scanning probe current of PEC treated aluminum were respectively 1/3 and 1/5 that of the aluminum substrate. After PEC treatment, the wear and corrosion resistances of pure aluminum were improved.