RESUMO
The article presents the dependence of the morphology as well as micromechanical and sclerometric properties of Al2O3 layers on the parameters of anodizing of aluminum alloys. The oxide layers were produced on the EN AW-5251 aluminum alloy by means of a direct current anodizing in a three-component electrolyte. The input variables (current density and electrolyte temperature) were selected based on the overall design of the experiment. The current density was 1, 2, 3 A/dm2, and the electrolyte temperature was 283, 293, 303 K. The surface morphology was examined using a scanning electron microscope (SEM), and then the microscopic images were analyzed using a graphics program. The micromechanical and sclerometric properties were examined by determining the HIT hardness and three critical loads: Lc1 (critical load at which the first damage of the tested layers occurred-Hertz tensile cracks inside the crack), Lc2 (critical load at which the first cohesive damage of the layers occurred) and Lc3 (load at which the layers were completely damaged). Sclerometric tests with the use of scratch tests were supplemented with pictures from a scanning microscope, showing the scratches. The produced layers are characterized by a hardness above 3 GPa and a porosity of 4.9-10.3%. Such a range of porosity of the produced layers allows their wide application, both for sliding associations with polymers and for their modification.
RESUMO
The article presents the effect of anodizing parameters of the EN AW-5251 aluminum alloy on the thickness and roughness of Al2O3 layers as well as their wettability and tribological properties in a sliding combination with the T7W material. The input variables were the current density of 1, 2, 3 A/dm2 and the electrolyte temperature of 283, 293, 303 K. The tribological tests were performed on the T-17 tester in reciprocating motion, in conditions of technically dry friction. The tests were carried out on a 15 km road with a constant average slip speed of 0.2 m/s and a constant unit pressure of 1 MPa. The measurement of the wettability of the layers was performed using the sitting drop method, determining the contact angles on the basis of which the surface free energy was calculated. The profilographometric measurements were made. The analysis of the test results showed that the anodizing parameters significantly affect the thickness of the Al2O3 layers. The performed correlation analysis also showed a significant relationship between the roughness parameters and the wettability of the surface of the layers, which affects the ability to create and maintain a sliding film, which in turn translates into sliding resistance and wear of the T7W material. The analysis of friction and wear tests showed that the layer with hydrophobic properties produced at a current density of 1 A/dm2 in an electrolyte at a temperature of 283 K is the most favorable for sliding associations with T7W material.
RESUMO
The article presents the effect of the thermo-chemical treatment of Al2O3 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 (AlMg2) 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 Na2SO4·10H2O and Na2Cr2O7·2H2O. 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 Na2SO4·10H2O and Na2Cr2O7·2H2O 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 Na2SO4·10H2O solution and a decrease in the case of the layers modified in the Na2Cr2O7·2H2O solution. The highest microhardness (7.1 GPa) was exhibited by the layer modified in the Na2SO4·10H2O 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 Na2SO4·10H2O 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.
RESUMO
The paper presents the influence of the surface anodizing parameters of the aluminum alloy EN AW-5251 on the physicochemical properties of the oxide layers produced on it. Micrographs of the surface of the oxide layers were taken using a scanning electron microscope (SEM). The chemical composition of cross-sections from the oxide layers was studied using energy dispersive spectroscopy (EDS). The phase structure of the Al2O3 layers was determined by the pattern method using X-ray diffractometry (XRD). The nanomorphology of the oxide layers were analyzed based on microscopic photographs using the ImageJ 1.50i program. The energetic state of the layers was based on the surface-free energy (SFE), calculated from measurements of contact angles using the Owens-Wendt method. The highest surface-free energy value (49.12 mJ/m²) was recorded for the sample produced at 293 K, 3 A/dm², in 60 min. The lowest surface-free energy value (31.36 mJ/m²) was recorded for the sample produced at 283 K, 1 A/dm², in 20 min (the only hydrophobic layer). The highest average value nanopore area (2358.7 nm²) was recorded for the sample produced at 303 K, 4 A/dm², in 45 min. The lowest average value nanopore area (183 nm²) was recorded for the sample produced at 313 K, 1 A/dm², in 20 min.
