MARIANA XAVIER MILAGRE

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Data final: 2019 × Data inicial: 2019 × Percentil: 25.00 - 49.99 ×

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    Artigo IPEN-doc 26650
    Correlating the modes of corrosion with microstructure in the friction stir welded AA2198-T8 alloy in aqueous hydrogen peroxide-chloride medium
    2019 - MACHADO, CARULINE de S.C.; DONATUS, UYIME; MILAGRE, MARIANA X.; MOGILI, NAGA V.V.; GIORJÃO, RAFAEL A.R.; KLUMPP, RAFAEL E.; ARAUJO, JOAO V. de S.; FERREIRA, RAPHAEL O.; COSTA, ISOLDA
    In this study, different types of localized corrosion in the friction stir welding (FSW) zones of an AA2198-T8 when the alloy is subjected to a corrosion test in a hydrogen peroxide–chloride solution (according to ASTM G110 standard) has been investigated. The corrosion modes were correlated with microstructure, especially with respect to the T1 phase and coarse Al-Cu-Fe phase distribution across the weldment. Simulated thermal profile and microhardness measurements were used to establish the variations in T1 phase distribution. Two types of corrosion were observed in the FSW zones: intense pitting and intergranular corrosion—type I; and the formation of cavities and trenches—type II. Type I is associated with the T1 phase while type II is associated with Al-Cu-Fe coarse intermetallics. Both types were found on the base metal (BM) and heat affected zone, but the type I reduced in the latter toward the stir zone (SZ). The SZ/thermomechanically affected zone (TMAZ) exhibited only type II. Also, Cu enrichment was observed around the type II sites in the SZ/TMAZ. Furthermore, an inverse correlation between microhardness and corrosion resistance which was related to T1 phase concentration in the different zones was also observed. Moreover, the SZ and BM were isolated and evaluated by an immersion test and electrochemical analysis using the ASTM G110 test solution. The results indicated galvanic coupling effects, as the SZ was strongly attacked when exposed separately compared to when it was coupled with the other zones.
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    Artigo IPEN-doc 25749
    Comparison of the corrosion resistance of an Al–Cu alloy and an Al–Cu–Li alloy
    2019 - MILAGRE, MARIANA X.; DONATUS, UYIME; MACHADO, CARULINE S.C.; ARAUJO, JOAO V.S.; SILVA, REJANE M.P. da; VIVEIROS, BARBARA V.G. de; ASTARITA, ANTONELLO; COSTA, ISOLDA
    In this study, the corrosion mechanisms of the AA2024-T3 and the AA2098-T351 were investigated and compared using various electrochemical techniques in 0.005 mol L−1 NaCl solution. The severe type of corrosion in the AA2098-T351 was intragranular attack (IGA) although trenching and pitting related to the constituent particles were seen. On the other hand, the AA2024-T3 exhibited severe localised corrosion associated with micrometric constituent particles, and its propagation was via grain boundaries leading to intergranular corrosion (IGC). Electrochemical techniques showed that the corrosion reaction in both alloys was controlled by diffusion. The non-uniform current distribution in both alloys showed that EIS was not a proper technique for comparing the corrosion resistance of the alloys. However, local electrochemical techniques were useful for the evaluation of the corrosion resistance of the alloys.