Vapour composition and activities in Mg-Zn liquid alloy at 923 K

Vapour species effusing from a magnesia Knudsen cell containing Mg-Zn alloy at 923 K were condensed on a water cooled copper plate. The equilibrium composition of the vapour phase over the alloy was determined from chemical analysis of the condensate. The activity coefficients of both components in the alloy have been derived from the data using a modified Gibbs-Duhem relation. The ratio of saturation vapour pressures of pure Zn and Mg obtained from the analysis of alloy data agree well with values from the literature, providing an internal check on the accuracy of data obtained in this study. Both components of the alloy exhibit negative deviations from Raoult's law. The concentration-concentration structure factor of Bhatia and Thomton at zero wave vector, evaluated from the measurements, indicate the presence of MgZn2 type complex in the liquid state. The associated regular solution model has been used for the thermodynamic description of liquid Mg-Zn alloys.

Electron-metallographic studies of precipitation in an aluminium-zinc-magnesium alloy

The mechanism of sub-microscopic precipitation in an Al-Zn-Mg alloy selected for its maximum response to ageing has been studied by a standardized oxide-replica technique in a 100 kV. Philips Electron Microscope. Contrary to earlier conclusions, examination of the oxide replicas has been shown to reveal details of the precipitation process almost as clearly as the thin-foil transmission technique. The reported formation of spherical Guinier-Preston zones followed by the development of a Widmanstaetten pattern of precipitated platelets has been confirmed. The zones have, however, been shown to grow into the platelets and not to dissolve in the matrix as reported earlier. The precipitation process has been correlated with the Hardness/Ageing Time curve and the structure of the precipitates has also been discussed.

Effect of matrix strength on the mechanical properties of Al-Zn-Mg/SiCp composites

The mechanical properties of Al-Zn-Mg alloy reinforced with SiCP composites prepared by solidification route were studied by altering the matrix strength with different heat treatments. With respect to the control alloy, the composites have shown similar ageing behaviour in terms of microhardness data at 135 degrees C. It was shown that although composites exhibited enhanced modulus values, the strengthening was found to be dependent on the damage that is occurring during straining. Thus the initial matrix strength plays an important role in determining the strengthening. Consequently, compression data had shown a different trend compared to tension. (C) 2000 Elsevier Science Ltd. All rights reserved.

Three-Dimensional simulation of deformation fields underneath vickers indenter:Effects of power-law Plasticity

The effects of power-law plasticity (yield strength and strain hardening exponent) on the plastic strain distribution underneath a Vickers indenter was systematically investigated by recourse to three-dimensional finite element analysis, motivated by the experimental macro-and micro-indentation on heat-treated Al-Zn-Mg alloy. For meaningful comparison between simulated and experimental results, the experimental heat treatment was carefully designed such that Al alloy achieve similar yield strength with different strain hardening exponent, and vice versa. On the other hand, full 3D simulation of Vickers indentation was conducted to capture subsurface strain distribution. Subtle differences and similarities were discussed based on the strain field shape, size and magnitude for the isolated effect of yield strength and strain hardening exponent.

An electron microscopic study of quasicrystals in a quaternary alloy : Mg32(Al, Zn, Cu)49

The discovery of a solid exhibiting m 3 5 point group symmetry by Shechtman et. al. (l) in a rapidly solidified Al-14at%Mn alloy has activated intensive studies of a new class of solids, termed as quasicrystals (2). While the original discovery reported the existence of quasicrystals in AI-Mn. AI-Fe and AI-Cr alloys, subsequent work has revealed their existence in Mg-Zn-Al(3,4), Mg-A]-Cu(5), AI-Mn-Si(6) and Ti-Ni-V(7) alloys (Table l).

Study of (Ba3MMWO9)-M-II-W-IV (M-II = Ca, Zn; M-IV = Ti, Zr) perovskite oxides: Competition between 3C and 6H perovskite structures

We describe an investigation of (Ba3MMWO9)-M-II-W-IV oxides for M-II = Ca, Zn, and other divalent metals and M-IV = Ti, Zr. In general, a 1:2-ordered 6H (hexagonal, P6(3)/mmc) perovskite structure is stabilized at high temperatures (1300 degrees C) for all of the (Ba3MTiWO9)-Ti-II oxides investigated. An intermediate phase possessing a partially ordered 1:1 double perovskite (3C) structure with the cation distribution, Ba-2(Zn2/3Ti1/3)(W2/3Ti1/3)O-6, is obtained at 1200 degrees C for Ba3ZnTiWO9. Sr substitution for Ba in the latter stabilizes the cubic 3C structure instead of the 6H structure. A metastable Ba3CaZrWO9 that adopts the 3C (cubic, Fm (3) over barm) structure has also been synthesized by a low-temperature metathesis route. Besides yielding several new perovskite oxides that may be useful as dielectric ceramics, the present investigation provides new insights into the complex interplay of crystal chemistry (tolerance factor) and chemical bonding (anion polarization and d(0)-induced distortion of metal-oxygen octahedra) in the stabilization of 6H versus 3C perovskite structures for the (Ba3MMWO9)-M-II-W-IV series.

Study of (Ba3MMWO9)-M-II-W-IV (M-II = Ca, Zn; M-IV = Ti, Zr) perovskite oxides: Competition between 3C and 6H perovskite structures

We describe an investigation of (Ba3MMWO9)-M-II-W-IV oxides for M-II = Ca, Zn, and other divalent metals and M-IV = Ti, Zr. In general, a 1:2-ordered 6H (hexagonal, P6(3)/mmc) perovskite structure is stabilized at high temperatures (1300 degrees C) for all of the (Ba3MTiWO9)-Ti-II oxides investigated. An intermediate phase possessing a partially ordered 1:1 double perovskite (3C) structure with the cation distribution, Ba-2(Zn2/3Ti1/3)(W2/3Ti1/3)O-6, is obtained at 1200 degrees C for Ba3ZnTiWO9. Sr substitution for Ba in the latter stabilizes the cubic 3C structure instead of the 6H structure. A metastable Ba3CaZrWO9 that adopts the 3C (cubic, Fm (3) over barm) structure has also been synthesized by a low-temperature metathesis route. Besides yielding several new perovskite oxides that may be useful as dielectric ceramics, the present investigation provides new insights into the complex interplay of crystal chemistry (tolerance factor) and chemical bonding (anion polarization and d(0)-induced distortion of metal-oxygen octahedra) in the stabilization of 6H versus 3C perovskite structures for the (Ba3MMWO9)-M-II-W-IV series.

Clustering phenomena in Al-4.4 at. % Zn alloy with 0.03 and 0.08 at. % Ag additions

The influence of 0.03 and 0.08 at. % Ag additions on the clustering of Zn atoms in an Al-4.4 at. % Zn alloy has been studied by resistometry. The effect of quenching and ageing temperatures shows that the ageing-ratio method of calculating the vacancy-solute atom binding energy is not applicable to these alloys. Zone-formation in Al-Zn is unaffected by Ag additions, but the zone-reversion process seems to be influenced. Apparent vacancy-formation energies in the binary and ternary alloys have been used to evaluate the v-Ag atom binding energy as 0.21 eV. It is proposed that, Ag and Zn being similar in size, the relative vacancy binding results from valency effects, and that in Al-Zn-Ag alloys clusters of Zn and Ag may form simultaneously, unaffected by the presence of each other. © 1970 Chapman and Hall Ltd.

Clustering and solute-vacancy binding energies in Al-4.4% Zn alloy with 0.01% ternary additions

Isochronal and isothermal ageing experiments have been carried out to determine the influence of 0.01 at. % addition of a second solute on the clustering rate in the quenched Al-4,4 a/o Zn alloy. The influence of quenching and ageing temperatures has been interpreted to obtain the apparent vacancy formation and vacancy migration energies in the various ternary alloys. Using a vacancy-aided clustering model the following values of binding free energy have been evaluated: Ce-0.18; Dy-0.24; Fe-0.18; Li-0.25; Mn-0.27; Nb-0.18; Pt-0.23; Sb-0.21; Si-0.30; Y-0.25; and Yb-0.23 (± 0.02 eV). These binding energy values refer to that between a solute atom and a single vacancy. The values of vacancy migration energy (c. 0.4 eV) and the experimental activation energy for solute diffusion (c. 1.1 eV) are unaffected by the presence of the ternary atoms in the Al-Zn alloy.

Strain-rate sensitivity and microstructural evolution in a Mg-Al-Zn alloy

Strain rate sensitivity measurements are used to identify twinning and changes in deformation mechanisms in a Mg AZ31 alloy over a wide range of temperatures and grain sizes. At low temperatures, there is significant twinning at low strains with strain-rate insensitivity; at large strains, strain rate sensitivity is noted, corresponding to deformation by multiple slip. At high temperatures, there is very little twinning and this leads to a significant strain rate sensitivity from the early stages of deformation. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Formation of a single, rotated-Brass (1 1 0)< 5 5 6 > texture by hot cross-rolling of an Al-Zn-Mg-Cu-Zr alloy

The present work describes the evolution of a strong, single-component rotated-Brass ((1 1 0) < 5 5 6 >) texture in an Al-Zn-Mg-Cu-Zr alloy by an uneven hot cross-rolling with frequent interpass annealing. This texture development is unique because hot rolling of aluminum alloys results in orientation distribution along the ``beta-fibre''. It has been demonstrated that the deformation by cross-rolling of a partially recrystallized grain structure having rotated-Cube and Goss orientations, and the recrystallization resistance of near-Brass-oriented elongated grains play a critical role in development of this texture. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A comparative study of the interaction of CO with Cu and Cu-Zn alloy clusters

Interaction of CO with Cu clusters deposited on a ZnO(0001) crystal and on ZnO/Zn surfaces (prepared in the electron spectrometer) has been examined by UV and X-ray photoelectron spectroscopy. The interaction is stronger with the small Cu clusters deposited on ZnO/Zn surfaces. Interaction of CO is evert stronger with annealed Cu/ZnO/Zn surfaces where Cu-Zn alloy particles are present. Copyright (C) 1996 Published by Elsevier Science Ltd