Abstract
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.
Highlights
Among other things, in order to increase the hardness and abrasion resistance of an aluminum surface layer, oxide layers are formed on its surface
On the basis of the research conducted and analysis of the results, it can be concluded that the Al2 O3 layers subjected to the thermo-chemical treatment processes in distilled water, Na2 SO4 ·10H2 O and Na2 Cr2 O7 ·2H2 O solutions are characterized by complete surface coverage of the applied treatment products
The analysis of the chemical composition of the layers revealed the presence of elements included in the solutions used in the thermochemical treatment process, which proves that the compounds from these solutions are incorporated into the nanostructure of the layers
Summary
In order to increase the hardness and abrasion resistance of an aluminum surface layer, oxide layers are formed on its surface. Thermo-chemical treatment carried out in nickel fluoride solutions [17,18,19] gives good results in anti-corrosion protection. It is performed in 5–15 min, at temperatures of 303–323 K. The thermo-chemical treatment of oxide layers employing the above methods is a procedure that primarily protects the base of the layers against corrosion. Thermo-chemical treatment carried out in order to increase the wear resistance of the oxide layers should be performed in conditions where the nanostructure of the layers will not be hydrated too much and in chemical compounds resulting in the formation of a sub-layer with good sliding properties.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
