Abstract
The constituent particles of AA2024-T3 Al alloys were identified and their microstructural change after alkaline degreasing, acidic desmutting, and zirconium (Zr) conversion coating was detailed. The constituent particles of AA2024-T3 included Al-Cu-Fe-Mn, θ-Al2Cu, and S-Al2CuMg, and were several micrometers in size. All these three particles were cathodic to the Al matrix after alkaline degreasing and acidic desmutting pretreatment. The OCP evolution in the Zr conversion bath revealed that the conversion coating reactivity of the as-polished AA2024-T3 was promoted after the pretreatment. The polarization test in 0.1 M Na2SO4 + 0.05 M NaCl solution showed that the cathodic kinetics were enhanced after the pretreatment. Subsequent Zr conversion coating inhibited the anodic kinetics but did not alter the cathodic kinetics in chloride solutions. The defects of ZrO2 coating were responsible for the insignificant change in the cathodic activities.
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