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Temperature and time dependences of the magnetization of Al-Zn-Mg alloys with varying Zn to Mg ratios (Zn/Mg = 0.25, 0.5, 1, 2, 5.5, and 9, keeping the total concentration of Zn plus Mg to be 5 at. %) were studied in the range from 10 to 310 K after various periods of natural aging. In particular, for Al1−y(Mg2Zn11)y alloys, the total concentrations of Zn and Mg were also varied from 2 to 20 at. % (y = 0.02, 0.03, 0.04, 0.05, 0.1, and 0.2). The largest time variant enhanced diamagnetism was observed for Al0.95(Mg2Zn11)0.05 as a result of solution heat treatment/quenching and natural aging. Isothermal measurements of magnetization vs time for natural aging temperatures from 260 to 300 K for Al0.95(Mg2Zn11)0.05 provided activation energies for solute clustering: 0.69 ± 0.05 eV (for stages I and II) and 0.78 ± 0.03 eV (for stages II and III). The mechanical hardness vs time at 273 K for Al0.95(Mg2Zn11)0.05 confirmed that the time variation of magnetization was related to the precipitation process of Zn/Mg/vacancy zones. Additionally, temperature dependences of the magnetization of Mg21Zn25, Mg4Zn7, MgZn2, and Mg2Zn11 were examined. The observed magnetization for the Mg-Zn compounds was found to be too small to account for the enhanced diamagnetic contributions to magnetization of Al-Zn-Mg alloys. A possible Zn-Mg-vacancy atomic arrangement responsible for the enhanced diamagnetism is discussed. [ABSTRACT FROM AUTHOR]

High angle annular dark field scanning transmission electron microscopy has been employed to observe precipitate structures in Al–Zn–Mg and Mg–Zn alloys. precipitate structures in Al–Zn–Mg are commonly formed by MgZn2 Penrose bricks, but also frequently observed to incorporate Mg6Zn7 elongated hexagons via two different modes. Tilings of MgZn2 and Mg6Zn7 building blocks in both in Mg–Zn and in Al–Zn–Mg alloys, create overall patterns which deviate from the chemical and structural configuration of solely monoclinic Mg4Zn7 or MgZn2 unit cells. Precipitate morphologies were found to be correlated to their internal sub-unit cell arrangements, especially to Mg6Zn7 elongated hexagons. Systematic or random arrangements of Mg6Zn7 elongated hexagons inside precipitates and therefore compositional and structural patterns, were found to be strongly related to the aspect ratio of the precipitates and altering of the precipitate/matrix interfaces. [ABSTRACT FROM AUTHOR]

The microstructures of precipitates in Al-Zn-Mg alloys in peak-aged condition have been studied using scanning transmission electron microscope. The same thermo-mechanical treatment was applied in all alloys. Investigation of peak-aged samples revealed that the most commonly found phases were η′ and η with their respective habit planes on {111} and {100}. η′ phases under [110] were analyzed and compared with η′ structure models. Furthermore, a close inspection of η phase as the second most found precipitate revealed that it incorporates an anti-phase resembling boundary, not observed in other orientation relationships that precipitates create with Al matrix, in addition, differences in matrix-precipitate interfaces between η′/ η and η phases were noticed. This paper addresses the first part to the analysis of η′ phase. Next part is extended to the analysis of the η phase. [ABSTRACT FROM AUTHOR]

To provide atomic scale understanding of the initial corrosion process of Fe in aqueous environment, the electronic interaction of between water molecules and hydroxyl groups with the (110) and (100) surface of Fe is investigated in a density functional theory approach. Using periodic slab models, stable structures and electronic states are calculated, and the dynamical behavior of water molecules and hydroxylated iron surface under finite temperature is resolved by first-principles molecular dynamics. The position of hydroxyl groups on surface does not change from the initial bridge position, while water molecules move from the initial on-top to bridge site, and the molecular surface tilts from a parallel position, the hydrogen bonds are also formed between water molecules and hydroxyl groups. This result suggests that the interaction due to the hydrogen bonding is dominant. [ABSTRACT FROM PUBLISHER]

• Abnormally enhanced paramagnetism observed for Al 12 Mg 17 and Al 44 Mg 56 compounds, while diamagnetism for Al 45 Mg 55. • The substitution of either element for the host produced diamagnetic contributions to the magnetization. • DFT calculations could not explain observed drastic variations of the magnetization of Al-Mg compounds. Magnetization (M) of binary Al-Mg alloys and intermetallic compounds were measured in the temperature (T) range from 10 to 300 K. The Al-rich alloys Al - 2, 3, 4, 5, and 10 at% Mg) revealed diamagnetic contributions to the magnetization correlating to the Mg concentrations. For the β-phase Al 3 Mg 2 the M vs T curve lay very close to that of pure Mg over the entire measured T region. The magnetization of the γ-phase samples exhibited enhanced paramagnetism for Al 44 Mg 56 and Al 12 Mg 17 , but the diamagnetism for Al 45 Mg 55. There were diamagnetic contributions to the magnetization of the Mg-rich alloys (Mg - 5, 10, and 15 at% Al) depending on the Al concentration, possibly due to the γ-phase precipitations. Heat capacity of the γ-phase samples and pure Al were measured to estimate the electronic specific heat coefficients which were found to be almost the same. Density functional theory calculations for the Al-Mg compounds were carried out to aid interpretation of the observed magnetization. [ABSTRACT FROM AUTHOR]

Characterization of precipitates in Al-Zn-Mg alloys, using a combination of electron diffraction, bright field transmission electron microscopy and atomic scale scanning transmission electron microscopy imaging revealed the presence of an unreported η 13 orientation relationship between the η-MgZn 2 phase and the Al lattice with the following orientation relationship (0001) η ∥ (120) Al and (2 1 ¯ 1 ¯ 0) η ∥ (001) Al , plate on (120) Al. The precipitate interfaces were observed and analyzed along two projections 90° to one-another. The precipitate coarsening was through the common thickening ledge mechanism. The ledges were significantly stepped along one lateral direction. An interface relaxation model using density functional theory was carried out to explain the precipitate behavior. Image 1 • A new orientation relationship between the η-MgZn 2 hardening precipitate and the Al matrix has been established. • The precipiate interface was observed by HAADF-STEM in two projections, 90° to one-another. • Thickening ledges were observed to be anistropically stepped depending on directional misfit. • DFT relaxation of interface model fairly well explains the significant stepped thickneing ledges along the highest directional misfit. [ABSTRACT FROM AUTHOR]