Abstract
Intergranular corrosion (IGC) and pitting transition caused by grain boundary β-phase saturation of aluminum alloy AA5083 sensitized at 150 °C was investigated in 3.5 wt% NaCl solution. The change in the localized corrosion mechanism from IGC to pitting was studied by microstructural and electrochemical analysis, where IGC was found to be the primary mechanism at low degrees of sensitization (DoS) and pitting corrosion was observed to develop after grain boundary β-phase saturation. Evaluation of the double layer capacitance by electrochemical impedance spectroscopy (EIS) and charge passed through the specimens by potentiostatic current monitoring demonstrated a well differentiated three-stage dissolution mechanism.
Highlights
AA5XXX series aluminum alloys (AA) are non-heat-treatable and valued in marine and automotive applications for their corrosion resistance, strength, light weight and formability from solid solution strengthening and cold work [1,2,3]
Sensitization can cause the AA5083 to be highly susceptible to intergranular corrosion (IGC) and pitting corrosion due to the anodic behavior and preferential dissolution of the β-phase [10,11,12]
degree of sensitization (DoS) values above 25 mg/cm2 have been shown to be more variable; this can be attributed to the use of a high sensitization temperature at or above 150 ◦ C, which approaches the α + β → α phase transition, decreasing the equilibrium
Summary
AA5XXX series aluminum alloys (AA) are non-heat-treatable and valued in marine and automotive applications for their corrosion resistance, strength, light weight and formability from solid solution strengthening and cold work [1,2,3]. Significantly corrosion-resistant, these alloys contain a substantial amount of Mg supersaturated (4.5 wt%) above the solubility limit of 3 wt% Mg in Al; high Mg content provides increased solution strengthening, but can decrease the corrosion performance of the alloy if exposed to elevated temperatures [6,7]. Sensitization can cause the AA5083 to be highly susceptible to intergranular corrosion (IGC) and pitting corrosion due to the anodic behavior and preferential dissolution of the β-phase [10,11,12]. The accelerated corrosion behavior is caused by an increase in electrical conductivity and chemical reactivity from the Mg rich β-phase precipitates [13,14]. DoS values above 25 mg/cm have been shown to be more variable; this can be attributed to the use of a high sensitization temperature at or above 150 ◦ C, which approaches the α + β → α phase transition, decreasing the equilibrium
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