The influence of thermochemical treatment of Al2O3 layers on their chemical composition, nanostructure, micromechanical and sclerometric properties, and surface morphology is presented. By anodizing in a three-component direct current electrolyte, oxide layers were obtained by means of an aluminum alloy EN AW-5251 (AlMg2). Thermochemical treatment was carried out directly in aqueous solutions of Na2SO4·10H2O and Na2Cr2O7·2H2O, as well as in water purified from mineral salts. A thermochemical treatment method is presented that transforms the surface structure of the layers (formation of a sublayer of Na2Cr2O7·2H2O and Na2SO4·10H2O) and significantly changes the thickness of the layers by 0.37 and 1.77 microns, respectively. It was revealed that thermochemical treatment in water led to the formation of a sublayer 0.63 microns thick. Micro-mechanical tests have shown an increase in the surface microhardness of layers in the case of their thermochemical treatment in water and Na2SO4·10H2O, as well as a decrease in layers modified in Na2Cr2O7·2H2O solution. The layer modified in Na2SO4·10H2O solution has the highest microhardness (7.1 GPa). Scratch tests indicate that thermochemically treated layers have better adhesive properties than the control layer. The optimal constancy with respect to scratches was demonstrated by the layer as a result of thermochemical treatment using a solution of 10H2O · Na2SO4 (the highest values for almost most critical loads), relates it to sliding contacts, which is provided with high load capacity and insignificant roughness.