Electrochemical methods for corrosion testing of Ce-based coating prepared on AA6060 alloy by dip immersion method

Abstract

Dip-immersion is simple and cost-effective method for the preparation of Ce-based conversion coatings (CeCCs), a promising alternative to the toxic chromate coatings, on the metal substrates. In this work CeCCs were prepared on Al-alloy AA6060 from aqueous solution of cerium chloride at room temperature. Effect of immersion time and post-treatment in phosphate solution on the microstructure and corrosion properties of the coatings was studied. The longer immersion time, the thicker but nonhomogeneous and cracked CeCCs. The post-treatment contributed to the sealing of cracks, as proven by an increase in corrosion resistance compared with as-deposited coatings. CeCCs prepared at longer deposition time and post-treated showed much better corrosion protection than those prepared at short deposition time. A detailed EIS study was undertaken to follow the evolution of corrosion behaviour of CeCCs with time of exposure to aggressive chloride environment (3.5 % NaCl). For the sake of comparison, the EIS properties of bare AA6060 were also investigated. A linear voltammetry was performed to complete the study. Results confirmed a formation of protective CeCCs on AA6060 surface. However, even CeCCs prepared at longer deposition time and post-treated provided a short term protection in aggressive environment, due to the small thickness. [Projekat Ministarstva nauke Republike Srbije, br. III 45019 i br. III 45012

Improved performance of cerium conversion coatings on steel with zinc phosphate post-treatment

“…However, the improvement has not been significant due to non-compact and porous structure of the coating creating the pathways for the electrolyte diffusion. Recent findings have revealed that post-treatment of the steel substrates in the chemical bathes including cerium and zinc phosphate conversion coatings could improve the surface properties and anticorrosion performances of the substrate [31][32][33][34][35].…”

Impedance characteristics of aluminum with sol-gel ceria protective coating during the exposure to chloride corrosion agent

“…Najbolje zaštitne karakteristike pokazale su prevlake oksida retkih zemalja [2,3], u prvom redu oksida cerijuma [4][5][6][7][8]. Pokazano je da različiti postupci nanošenja prevlake oksida cerijuma, zasnovani na raspršivanju, potapanju u rastvor cerijumovih jona, indirektnom elektrotaloženju ili sol-gel postupku, dovode do različitih zaštitnih karakteristika, uglavnom zbog različite morfologije nanete prevlake [8][9][10][11][12][13][14][15][16] Imajući u vidu da različiti postupci dobijanja prevlake znatno utiču na njenu morfologiju, i posledično na njena zaštitna svojstva, detaljno razumevanje procesa koji se odigravaju tokom izlaganja sistema prevlaka/podloga korozionoj sredini je od velikog značaja za odgovarajuću modifikaciju postupka dobijanja prevlake, kako bi ona imala željene zaštitne karakteristike u datom slučaju. Kako bi se detaljno sagledale karakteristike prevlake oksida cerijuma na aluminijumu, i njihove promene tokom procesa izlaganja korozionoj sredini, analizirani su impedansni odzivi ovog sistema sa različitim ekvivalentnim kolima sa elementima kola kojima se može pripisati različito ili alternativno fizičko tumačenje.…”

“…3 i 4, dok su vrednosti parametara kola dati u tabeli 1. Korišćena EEK se često sreću u literaturi [13,17,[23][24][25][26], a induktivni element je uključen u EEK na sl. 3a i c. U svim EEK električna svojstva pasivnog filma predstavljena su elementima CPE p i R dl u paralelnoj vezi, odnosno elementom sa konstantnim faznim pomerajem koji se odnosi na kapacitivnost filma (parametar n u svim slučajevima ima vrednosti u opsegu 0,84-0,92, tabela 1) i otpornošću u porama filma, redom.…”

Corrosion resistance of flaky aluminum pigment coated with cerium oxides/hydroxides in chloride and acidic electrolytes

“…The test was done only on the Al pellet through sealing other sides with a 3:1.2 mixture of beeswax and colophony resins, leaving an exposed area of 1 cm 2 for measurements. The impedance measurements were carried out using an AUTOLAB G1 device in 3.5 wt.% NaCl solution at room temperature (25 ). The test was done in a conventional three electrode cell consisting of aluminium pellet, saturated calomel and graphite wire as working, reference and counter electrodes, respectively.…”

“…For the Al pigments, the main mechanism of Ce layer precipitation is the chemical reactions between Al(OH) 3 -rich particles and the Ce 3+ or Ce 4+ cations, which results in cerium oxide/hydroxide deposition on the pigment surface (Eqs. 3 to 5) [25].…”