Tribological properties of Al2O3 layers after thermo-chemical treatment

Abstract

The article presents the influence of the thermo-chemical treatment of Al2O3 layers on their tribological properties. The Al2O3 layers were produced on the EN AW-5251 aluminium alloy by means of direct current anodizing in a three-component electrolyte. For the sake of comparison, some of the samples were thermochemically treated in three liquids (sodium sulphate solution, sodium dichromate solution, distilled water). The parameters of the production and thermo-chemical treatment were selected on the basis of two Hartley's plans. The tribological properties were determined on the basis of a tribological test carried out for a pin-on-disc friction pair on a T-17 tester in reciprocating motion. The tests were carried out in conditions of technically dry friction. Thanks to the tests, coefficient of friction µ and the mass wear, together with the intensity of the material wear were determined. The use of thermo-chemical treatment in the sodium dichromate solution contributed to an increase in coefficient of friction μ and a reduction in the wear intensity of the polymer from 36 μg/km (layer without thermo-chemical treatment) to 21.33 μg/km (layer after thermo-chemical treatment in the sodium dichromate solution).The conducted stereometric tests before and after the tribological test for selected samples allow the authors to state that the thermo-chemical treatment in the sodium dichromate solution increases the amplitude parameters of surface roughness. The study of the surface morphology of the layer with the lowest mass wear showed the formation of an additional sub-layer as a result of thermo-chemical treatment carried out in the sodium dichromate solution.