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The 2024 aluminum alloy has excellent mechanical and low corrosion due to the existence of the high Cu levels, which shortens its service life. In this paper, we have systematically investigated the mechanism of the influence of three elements (Sc, Zr, and Ag) on the microstructure and corrosion behavior of 2024 aluminum alloy after microalloying. The results showed that microalloying treatment of 2024 aluminum alloy reduced the dendritic spacing of cast aluminum alloy; decreased the sizes of Cu-rich intermetallic particles (Cu-IMPs) within the peak aging of the T6 alloy to make their distribution more uniform; and changed the grain boundary phases (GBPs) and precipitate-free zones (PFZs) width of the T6 alloy. Microalloying treatment significantly changed the corrosion resistance of the alloy. Both Zr and Ag elements significantly improved the corrosion resistance of the alloy and reduced IGC depth and electrochemical corrosion rate, however, the Sc elements deteriorated the corrosion resistance of the alloy. Moreover, the corrosion mechanism of the alloy was also discussed in detail. • The PFZ of 2024 aluminum alloy can be narrowed by microalloying Zr and Ag elements, while the PFZ can be broadened by Sc elements. • Microalloying of Al-Cu-Mg alloy with Zr and Ag elements can reduce the corrosion susceptibility of the alloy. • The aggregate of Zr elements near the GBs forms Al 3 Zr particles, which prevent the formation of GBP of 2024Z alloy. [ABSTRACT FROM AUTHOR]

This study delved into the influence of Mg content on the microstructure and corrosion behavior of homogenized Al-Zn-Mg-Cu alloys. The findings unveiled that alloys featuring a moderate Mg content showcased an exceptionally low immersion corrosion rate of 0.0789 mm/a. A notable 22.3 % reduction in average grain size led to a significant 57.2 % drop in immersion corrosion rate. Furthermore, the augmentation of the Mg(Zn, Al, Cu) 2 phase within the grains contributed to a decrease in the maximum immersion corrosion depth of the alloy. These novel findings offer fresh insights and hold potential for enhancing the corrosion resistance of homogenized Al-Zn-Mg-Cu alloys. [Display omitted] • Alloys featuring a moderate Mg content showcased an exceptionally low immersion corrosion rate of 0.0789 mm/a. • A notable 22.3 % reduction in average grain size led to a significant 57.2 % drop in immersion corrosion rate. • The augmentation of the Mg(Zn, Al, Cu) 2 phase contributed to a decrease in the maximum immersion corrosion depth. [ABSTRACT FROM AUTHOR]

Mg alloys are widely used in the fields of aerospace, automotive, and electronic communication equipment. Understanding the corrosion behavior of Mg alloys is critical to prevent their catastrophic failures from the acid rain corrosion. The influences of heat treatment on corrosion behaviors of Mg-4Nd alloy in acid rains were investigated. The corrosion mechanisms of Mg-4Nd alloy are dominated by electrochemical and chemical corrosion, and the corrosion behaviors of Mg-4Nd alloy are affected by the concentrations of acid rain and heat-treated temperatures. Furthermore, Nd 2 O 3 are derived from the oxidation of exposed Nd atoms at the edge of precipitates and solid-solution atoms. [Display omitted] • The corrosion behaviors of Mg alloy in acid rain are affected by pH and precipitates. • Corrosion behaviors of Mg alloy in acid rain are dominated by electrochemical and chemical corrosion. • The micro-galvanic corrosion occurs between Mg 41 Nd 5 and Mg 12 Nd. • Nd 2 O 3 comes from the oxidation of precipitates and solid-solution atoms in the corrosion process. • The Nd 2 O 3 embedded in corrosion product films prevents the attack of corrosive ions. [ABSTRACT FROM AUTHOR]

The effects of heat treatments on the microstructures and corrosion behaviors of extruded Mg-2Nd-2Zn alloys in 3.5% NaCl electrolyte were investigated. It was found that the average corrosion rate of solid solution Mg-2Nd-2Zn alloy is 45.86 mm/y, which is much lower than that of the as-extruded and solution-aged Mg alloys. The nano-scale oxides were formed by the oxidation of solid solution atoms during the corrosion process and filled into the porous corrosion product film, which was conducive to reducing the corrosion rates of Mg alloys. Therefore, the solid solution treatment remarkably improved the corrosion rate of Mg alloys. • Heat treatments remarkably increase the grain sizes of Mg alloys and reduce grain boundary corrosion. • The corrosion products of Mg-2Nd-2Zn alloy are mainly composed of Mg(OH) 2 and Mg 2 Cl (OH) 3 ·4H 2 O. • Cl- attacks Mg(OH) 2 to form loose Mg 2 Cl(OH) 3 ·4H 2 O, resulting in a poor corrosion resistance of Mg alloys in Cl- solution. • Nano-scale oxides of solute atomic embedded in corrosion product film improves the corrosion resistance of Mg alloys. [ABSTRACT FROM AUTHOR]

Abstract: The corrosion behavior of 28Cr–7Ni–O–0.34N duplex stainless steels in air-saturated 3.5-wt% NaCl solution at pH 2, 7, 10 and 27 °C was studied by the potentiodynamic method. Two types of microstructures were investigated: the as-forged duplex and microduplex (average austenite grain size 5–16 μm) structures. The austenite volume fractions of the tested steels were between 0.35 and 0.64. The nitrogen effect on corrosion behaviors of both duplex and microduplex stainless steels were the same. At pH 2, the corrosion potential increased when the nitrogen content increased, however, corrosion current density as well as corrosion rate decreased. At pH 7 and 10, the effect of nitrogen on corrosion potential and corrosion rate could not be observed. Corrosion potential at pH 10 was lower than at pH 7. Pitting potential increased when the nitrogen content in the tested steels increased at all tested pH. For the nitrogen effect on the passive current density, it seemed that only at pH 2, the average passive current densities reduced when the nitrogen content increased. Nitrogen may have participated in the passive film or has been involved in the reaction to build up passive film. The ammonium formation and nitrogen enrichment at the interface metal/passive film with adsorption mechanism were discussed. The dissolute nitrogen might have combined with the hydrogen ions in solution to form ammonium ions, resulting in increasing solution pH. The steel could then easily repassivate, hence the corrosion potential and pitting potential would increase. However, the ammonium formation mechanism could not explain the decrease of corrosion potential in basic solution. Nitrogen enrichment at the metal/passive film interface with adsorption mechanism seemed to be an applicable consideration in increasing pitting potential. However, this mechanism did not involve the ammonium ion formation. In general, for the duplex and microduplex stainless steels tested, nitrogen increased the general corrosion resistances in acid solution and pitting corrosion resistance at all solution pH. Metallographic observation in both tested duplex and microduplex steels after pitting corrosion at all tested pH revealed that, the corroded structure in the tested steels without nitrogen alloying was austenite, but those with nitrogen alloying was ferrite. Even though ferrite had a higher chromium content than austenite but higher dissolved nitrogen in austenite than in ferrite may have increased the pitting resistance equivalent number (PRE) of austenite to be higher than that of ferrite. [Copyright &y& Elsevier]