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 ...
