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Abstract
Corrosion inhibition of aluminum alloy AA6063-T5 by vanadates (NaVO3) 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 Al4.01MnSi0.74, Al1.69Mg4Zn2.31, and FeAl3 intermetallic phases (IMPs) and nanometer-sized CuAl2, ZnAl2, and Mg2Si 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 Mg2Si 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.
Highlights
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Corrosion inhibition by soluble vanadates have been studied in detail for alloy AA2024 by Frankel et al, and Buchheit et al.,[25,30,31,32,33] who showed that the inhibition effectiveness of vanadates is strongly related to the microstructure
In this paper we focus on microstructure characterization of the AA6063-T5 alloy and related local Volta potential assessments, and demonstrate the effectiveness of sodium vanadate for mitigating corrosion of AA6063-T5 in chloride-containing medium by electrochemical and weight loss measurements
Summary
0.45 0.50 0.10 0.10 0.60 0.10 0.20 0.15 < 0.15 Bal. is influenced by the composition of the alloy and its thermomechanical processing history. Point analyses were carried out at 10–15 kV to obtain quantitative chemical composition of large IMPs. Volta potential measurements.—Scanning Kelvin Probe Force Microscopy (SKPFM) measurements were carried out on the OP-S polished specimen using a Bruker Icon atomic force microscope in amplitude modulation (AM) and frequency modulation (FM) mode to measure the local Volta potential difference of the microstructure. The samples were taken out from the solutions in discrete time intervals, wiped with a paper tissue, immersed in 20% HNO3 for 1 minute to remove formed corrosion products, rinsed by deionized water, and placed in a desiccator to fully dry the specimen. Electrochemical measurements consisted of potentiodynamic polarization scans and electrochemical impedance spectroscopy (EIS), which were performed on specimens exposed to aqueous 0.05 M NaCl solution with and without 3 mM NaVO3 for 1 and 24 hours, respectively. The ZView 3.2 and Nova 1.11 software were used for data analysis and spectra fitting
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