Nanostructure and Morphology of the Surface as Well as Micromechanical and Sclerometric Properties of Al(2)O(3) Layers Subjected to Thermo-Chemical Treatment

The article presents the effect of the thermo-chemical treatment of Al(2)O(3) layers on their nanostructure, surface morphology, chemical composition as well as their micromechanical and sclerometric properties. Oxide layers were produced on EN AW-5251 aluminium alloy (AlMg(2)) by the method of direct current anodizing in a three-component electrolyte. The thermo-chemical treatment was carried out in distilled water and aqueous solutions of Na(2)SO(4)·10H(2)O and Na(2)Cr(2)O(7)·2H(2)O. It was shown that the thermo-chemical treatment process changes the morphology of the surface of the layers (the formation of a sub-layer from the Na(2)SO(4)·10H(2)O and Na(2)Cr(2)O(7)·2H(2)O solutions), which directly increases the thickness of the layers by 0.37 and 1.77 µm, respectively. The thermo-chemical treatment in water also resulted in the formation of a 0.63 µm thick sub-layer. The micromechanical tests indicated a rise in the surface microhardness of the layers in the case of their thermo-chemical treatment in water and the Na(2)SO(4)·10H(2)O solution and a decrease in the case of the layers modified in the Na(2)Cr(2)O(7)·2H(2)O solution. The highest microhardness (7.1 GPa) was exhibited by the layer modified in the Na(2)SO(4)·10H(2)O solution. Scratch tests demonstrated that the thermo-chemically treated layers had better adhesive properties than the reference layer. The best scratch resistance was exhibited by the layer after thermo-chemical treatment in the Na(2)SO(4)·10H(2)O solution (the highest values, practically for all the critical loads) which, together with its low roughness and high load capacity, predispose it to sliding contacts.