Corrosion Inhibition of Aluminum Alloy AA6063-T5 by Vanadates: Microstructure Characterization and Corrosion Analysis

Abstract

Corrosion inhibition of aluminum alloy AA6063-T5 by vanadates (NaVO 3 ) in 0.05 M NaCl solution has been investigated by electrochemical and weight loss measurements, and associated with microstructure and Volta potential data. X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy analyses confirmed the presence of micrometer-sized Fe-rich Al 4.01 MnSi 0.74 , Al 1.69 Mg 4 Zn 2.31 , and FeAl 3 intermetallic phases (IMPs) and nanometer-sized CuAl 2 , ZnAl 2 , and Mg 2 Si precipitates in the microstructure. Scanning Kelvin probe force microscopy measurements showed Volta potential differences of up to 600 mV between the microstructure constituents indicating a high susceptibility to micro-galvanic corrosion, with interphase boundary regions exhibiting the highest propensity to corrosion. Most IMPs had cathodic character whereas some nanometer-sized Mg-rich particles exhibited anodic nature, with large Volta potential gradients within interphase regions of large cathodic particles. Electrochemical potentiodynamic polarization measurements indicated that the vanadates provided mixed corrosion inhibition effects, mitigating both oxygen reduction, occurring on cathodic IMPs, and anodic metal dissolution reaction, occurring on anodic sites, such as Mg 2 Si and interphase boundary regions. Electrochemical measurements indicated that the sodium metavanadate inhibitor blocks active metal dissolution, giving high inhibition efficiency (>95%) during the initial exposure, whereas long-term weight loss measurements showed that the efficacy decreases after prolonged exposure. Aluminum and its alloys are attractive materials for a range of industrial applications due to cost-efficient recyclability, excellent physical and mechanical properties, such as low density, high thermal conductivity, good weldability, and high strength-to-weight ratio. [1][2][3][4] In particular, the 6xxx-series (Al-Mg-Si) alloys are widely used in aerospace, automotive, marine, and construction industries due to their relatively good corrosion resistance, formability, and low cost as compared to the 2xxx (Al-Cu) and 7xxx (Al-Zn) alloys.5-7 However, these alloys contain multiple alloying elements and their microstructure is very heterogeneous, typically consisting of a large variety of intermetallic phases (IMPs), which makes them highly susceptible to localized corrosion such as pitting or intergranular corrosion. 5,8,9 While nanometer-sized IMPs, dispersed in the Al matrix, are desirable for mechanical strength of Al alloys, micrometer-sized IMPs may induce localized corrosion due to micro-galvanic coupling between the Al matrix and the IMPs, 10-12 which may also affect the anodization process. 13,14 IMPs play an important role in localized corrosion since their type, size, and distribution can affect electrochemical reactions, homogeneous chemical reactions as well as transport phenomena of molecular and ionic species. 8,15,16 Therefore, detailed knowledge about IMPs in the Al alloy is needed when exploring the mechanism ...

The Sealing Step in Aluminum Anodizing: A Focus on Sustainable Strategies for Enhancing Both Energy Efficiency and Corrosion Resistance

“…Coatings 2020, 10, 226 15 of 60 15% for AlO6. The roles that surface coordination plays in precipitation and dissolution of mineral phases had been discussed elsewhere [83][84][85][86].…”

“…Madden and Scully [210] had described in more detail how this might be possible with permanganate anion. This possibility is strengthened by the reported inhibitive effects of permanganates [210][211][212][213][214], tungstates [215][216][217], molybdates [67,152,[211][212][213][214][215][216][217][218][219][220], and vanadates [221][222][223][224][225][226][227] on aluminum corrosion and enhanced corrosion resistance of the anodic films formed on aluminum alloys. These anions are known to form "alumino-oxy" compounds with aluminum like chromate anion such as; aluminum tungstate [228][229][230], aluminum molybdate [231][232][233][234], aluminum permanganate [235,236], and aluminum vanadate [237].…”

“…Coatings 2020, 10, 226 35 of 60 both without compromising the quality of products. Application of insights highlighted earlier in sections 10.3.3 to 10.3.7 is likely to result in both improvements in the kinetics of the sealing step and the lowering of sealing bath operating temperatures, and hence improvements in the energy efficiency of the sealing step.…”

Corrosion properties of nickel coatings obtained from aqueous and nonaqueous electrolytes

“…Corrosion studies were carried out in three media: 0.5 M NaCl, 0.5 M H 2 SO 4 , and 2 M NaOH solutions at room temperature (≈ 20°C‐22°C). Concentrations of these media were selected based on the literature review . Potentiodynamic polarization scans and electrochemical impedance spectroscopy (EIS) tests were performed using an Autolab PGSTAT 302 N potentiostat‐galvanostat (Methrom Autolab, The Netherlands) in a three‐electrode glass cell.…”

Effects of the Combined Addition of Zn and Mg on Corrosion Behaviors of Electropainted AlSi-Based Metallic Coatings Used for Hot-Stamping Steel Sheets

“…They reported that the addition of Zn and Mg to AlSi-based coatings increases the corrosion resistance in chloride-containing environments. From a practical and an industrial point of view, however, lower concentrations of Zn and Mg, which have low melting temperatures, are favored to avoid the liquid metal embrittlement (LME) phenomenon [ 19 ] and localized corrosion attack caused by the selective dissolution of these alloying elements [ 6 , 20 ].…”