Vpliv parametrov anodizacije na lastnosti oksidnih prevlek na aluminiju in aluminijevih superplastičnih zlitinah : doktorska disertacija

Kern, Katarina (author), Bizjak, Milan (mentor), Karpe, Blaž (comentor)

Aluminij in njegove zlitine zaradi dobrih mehanskih, fizikalnih ter estetskih lastnosti ponujajo širok spekter uporabe tudi v arhitekturi in industrijskem oblikovanju. Pomembna prednost aluminija in njegovih zlitin je poleg njegovih mehanskih lastnosti ter možnosti preoblikovanja v kompleksne oblike tudi sposobnost prestrukturiranja površine izdelka, kar lahko popolnoma spremeni njegov izgled, ne da bi pri tem poslabšali njegove mehanske lastnosti. Najpogostejši postopek prestrukturiranja površine aluminija in njegovih zlitin je anodna oksidacija. S tem elektrokemijskim postopkom pripravimo na površini izdelka iz aluminija ali njegovih zlitin plast aluminijevega oksida (Al2O3), ki močno izboljša korozijsko odpornost in odpornost proti obrabi. Na lastnosti in kvaliteto izdelave te plasti pa imajo vpliv tako kemijska sestava zlitine in njena mikrostruktura, struktura površine izdelka kot tehnološki parametri anodne oksidacije. V zadnjih letih je bil dosežen pomemben napredek pri raziskovanju lastnosti nanoporoznih oksidnih prevlek tako z vidika vpliva kemijske sestave in metalurškega stanja aluminijskih zlitin kot tehnoloških parametrov anodne oksidacije. V prvi fazi raziskave smo se osredotočili na vpliv čistosti aluminija na mehanizem rasti in lastnosti oksidne prevleke. V ta namen smo z različnimi tehnološkimi parametri anodizirali tehnično čist (99,6 %) in rafiniran (99,998 %) aluminij. Sledila je raziskava mehanizma rasti oksidne plasti na aluminijevi zlitini z magnezijem (serija 5083). Magnezij ima namreč nižjo prosto tvorbeno energijo oksidacije od aluminija in se zato vgrajuje v nastajajočo oksidno plast. Ker je znano, da ima tudi mikrostruktura površine substrata velik vpliv na lastnosti oksidne prevleke, smo nadaljnje delo usmerili v raziskavo vpliva velikosti kristalnih zrn. Z različnimi tehnološkimi parametri smo anodizirali tehnično čist (99,6 %) aluminij in zlitino z magnezijem (serija 5083), ki sta imela udrobnjena kristalna zrna s postopkom tornega utrjevanja s trenjem in gnetenjem - FSP (ang. friction stir processing). Ker v literaturnih virih nismo zasledili raziskav anodiziranja superplastičnih zlitin, katerih uporaba se hitro povečuje, smo z različnimi tehnološkimi parametri anodizirali tudi zlitino serije 5083 mikrolegirano s skandijem. Povezavo med stanjem osnovnega materiala (substrata), procesnimi parametri anodiziranja in lastnostmi nastale oksidne prevleke smo analizirali s številnimi analitskimi tehnikami: optična mikroskopija (OM), elektronska vrstična mikroskopija (SEM), energijsko disperzna spektroskopija (EDS), mikroskopija na atomsko silo (AFM), meritve mikrotrdote ter meritve spektra odbojnosti vidne svetlobe s spektrometrom. V delu je opisan vpliv koncentracije elektrolita z žveplovo kislino ter vpliv temperature elektrolita v povezavi z vrsto in stanjem zgoraj navedenih zlitin na kinetiko rasti, morfologijo, mikrotrdoto ter reflektivnost nastale anodne plasti tako za potenciostatičen način (konstantna napetost) kot galvanostatičen način (konstantna gostota toka) anodiziranja.

• Language: Slovenian
• Keywords: anodna oksidacija, anodizacija, eloksacija, oksidne plasti, superplastične zlitine, torno utrjevanje z gnetenjem in mešanjem, odbojnost površin
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Place of publishing: Ljubljana
• Publisher: [K. Kern]
• Year: 2022
• Number of pages: XXXI, 171 str.
• PID: 20.500.12556/RUL-145307
• UDC: 669.1.094.3(043.3)
• COBISS.SI-ID: 150155011
• Publication date in RUL: 15.04.2023

Secondary language

• Language: English
• Title: Influence of anodizing parameters on the properties of the anodic coatings on aluminum and aluminium superplastic alloys : Ph. D. thesis

Abstract

Aluminium and its alloys offer a wide range of applications in architecture and industrial design. An important advantage of aluminium and its alloys in architecture is not only their mechanical properties and their ability to be transformed into complex shapes, but also their ability to restructure the surface of the product, which can completely change its appearance without compromising its mechanical properties. The most common surface restructuring process for aluminium and its alloys is anodic oxidation. This electrochemical process produces a layer of aluminium oxide (Al2O3) on the surface of an aluminium or aluminium alloy product, which greatly improves corrosion and wear resistance. The properties and quality of this layer are influenced by the chemical composition of the alloy and its microstructure, the surface structure of the product and the technological parameters of the anodic oxidation process. In recent years, significant progress has been made in the study of the properties of nanoporous oxide coatings, both in terms of the influence of the chemical composition and metallurgical state of aluminium alloys and the technological parameters of anodic oxidation. In the first phase of my research, we focused on the influence of aluminium purity on the growth mechanism and properties of the oxide coating. For this purpose, we anodised technically pure (99,6 %) and refined (99,998 %) aluminium using different technological parameters. Next, investigation of the growth mechanism of the oxide coating on an aluminium-magnesium alloy (series 5083) followed. As it is known that the microstructure of the substrate surface also has a significant influence on the properties of the oxide coating, we have focused further work on the influence of the crystal grain size. Using different technological parameters, we anodised technically pure (99,6 %) aluminium and magnesium alloy (series 5083), which had refined crystal grains by friction stir processing (FSP). Further we focus on anodising of superplastic aluminium 5083 alloys microalloyed with scandium, the use of which is increasing rapidly. The relationship between the state of the base material (substrate), the anodising process parameters and the properties of the resulting oxide coating was analysed by a number of analytical techniques: optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), atomic force microscopy (AFM), microhardness measurements, and reflectance spectrum of visible light measurements with a spectrometer. The influence of the electrolyte concentration (sulphuric acid) and the electrolyte temperature in relation to the type and condition of the above alloys on the growth kinetics, morphology, microhardness and reflectivity of the resulting anode layer is described for both potentiostatic (constant voltage) and galvanostatic (constant current density) modes of anodization.

• Keywords: anodic oxidation, anodization, oxide layers, superplastic alloys, friction stir processing, surface reflectivity