Characterization of oxide coatings formed by plasma electrolytic oxidation of aluminum in sodium tungstate

Abstract

This paper presents our recent research on morphology and phase composition of oxide coatings formed by plasma electrolytic oxidation of aluminum in 0.1 M sodium tungstate at constant current density of 15 mA/cm2 and corrosion stability of such coatings. Roughness of obtained oxide coatings increases with prolonged process time, while their microhardness reaches maximal value after about 5 minutes from the onset of the process and then decreases. Oxide coatings are partly crystallized and mainly consist of γ-Al2O3, α-Al2O3 i WO3, with γ-Al2O3 content increasing with prolonged PEO time. All obtained oxide coatings have higher impedance than pure aluminum and no relationship between PEO time and impedance is found. The evolution of impedance spectra shows that samples obtained after 7.5 minutes of PEO time have most efficient corrosion protection of aluminum substrate.

U radu su prikazana ispitivanja morfologije i faznog sastava površina oksidnih slojeva dobijenih metodom plazma elektrolitičke oksidacije aluminijuma u 0.1 M vodenom rastvoru natrijum volframatu pri stalnoj gustini struje od 15 mA/cm2, kao i njihova koroziona stabilnost. Pokazano je da hrapavost dobijenih slojeva raste sa vremenom trajanja procesa, dok mikro tvrdoća uzoraka dostiže maksimalnu vrednost posle 5 minuta od početka procesa i posle tog vremena opada. Osidni slojevi su delimično kristalizovane i uglavnom se sastoje od γ-Al2O3, α-Al2O3 i WO3, a sadržaj γ-Al2O3 raste sa trajanjem PEO procesa. Dobijeni oksidni slojevi imaju veću impedansu od čistog aluminijuma, pri čemu dužem vremenu PEO procesa ne odgovara i najveća impedansa. Najveću korozionu stabilnost su pokazali oksidni slojevi dobijeni posle 7.5 minuta odpočetka anodizacije.