Abstract
Magnesium-rich primers (MgRP) have generated great interest as a promising alternative to chromium-based primers for the protection of aluminum substrates but their performance during exterior exposure has not been well documented. This paper focuses on the evaluation of MgRP during natural weathering to gain insight into its mineralogical phase transformation and electrochemical nature. Control studies were conducted on Mg and AA2024-T3 coupons. The results indicate that Mg particles in MgRP transform into a variety of hydroxide, carbonate, and hydroxy carbonates. During natural weathering, CO2 inhibited the dissolution of both Mg and AA2024-T3 as a result of protective carbonate layer formation in the coating.
Highlights
Corrosion protection of aluminum alloys by Mg-rich primer (MgRP) is based on the principle of sacrificial cathodic polarization of aluminum by Mg
In our previous work [4], we investigated the behavioral dichotomy of Magnesium-rich primers (MgRP) exposed to salt spray testing (ASTM B117) and natural weathering
Reported that the NaCl-induced atmospheric corrosion of aluminum alloy AA 1070 is 10–20 times faster in CO2-free humid air compared to air containing ambient levels of CO2
Summary
Corrosion protection of aluminum alloys by Mg-rich primer (MgRP) is based on the principle of sacrificial cathodic polarization of aluminum by Mg. In our previous work [4], we investigated the behavioral dichotomy of MgRP exposed to salt spray testing (ASTM B117) and natural weathering (in a non-marine, non-urban environment). Lin et al studied the role of CO2 in the atmospheric corrosion of AZ91 Mg alloy in the presence of NaCl and concluded that CO2 inhibited NaCl-induced corrosion by generating slightly soluble hydroxy carbonates that provided a partly protective layer on the surface of the Mg alloy [5]. Cathodic polarization studies on Mg-rich primer coated AA2024-T3 alloy [6] indicated that CO2 in high concentrations buffers the pH on the AA2024-T3 surface and diminishes the extent of basic corrosion. Reported that the NaCl-induced atmospheric corrosion of aluminum alloy AA 1070 is 10–20 times faster in CO2-free humid air compared to air containing ambient levels of CO2. Mg particles (in Mg-rich primer) during natural weathering, the cathodic nature of Mg-rich primer (treated vs. untreated), and the impact of atmospheric CO2 on AA2024-T3 and the electrochemical nature of Mg
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