Effect of citrate additive on the electrodeposition and corrosion behaviour of Zn–Co alloy

The electrodeposition of Zn–15Co alloy on a stainless steel substrate from a citrate bath has been investigated as a function of pH and citrate concentration in the electroplating bath. UV–vis results and speciation diagrams of zinc and cobalt in aqueous citrate solution were used to select deposition baths with different dominant Zn–Co citrate complexes. Voltammetry and potentiostatic methods were used to study the codeposition mechanism. The corrosion behaviour of electrodeposits of Zn–15Co alloys was studied by means of electrochemical experiments in a solution of 3.5% NaCl using potentiodynamic polarisation and open circuit potential. The results showed that the corrosion resistance of the deposits was highly influenced by the presence of citrate in the electroplating bath.     

Predicting the size- and temperature-dependent shapes of precipitates in Al–Zn alloys

We study theoretically the size versus shape versus temperature relation of precipitates in Al–Zn via quantum-mechanical first-principles simulations. Our parameter-free model, based on a mixed-space cluster expansion, allows the prediction of the experimentally observed size and temperature dependences of the precipitate shape. We find that aging experiments can be explained in terms of equilibrium shapes. The precipitates change from a nearly spherical to a more ellipsoidal/hexagonal shape with increasing size and decreasing temperature. They always flatten in the [111] direction, which can be interpreted as a consequence of a mechanical instability of face-centered cubic Zn when rhombohedrally distorted along [111] and a strong anisotropy of the chemical energy. The excellent agreement between experiment and theory shows that our model can be used to quantitatively predict precipitate shapes and sizes.     

Effects of Cooling Rate and Component on the Microstructure and Mechanical Properties of Mg–Zn–Y Alloys

The microstructure and mechanical properties of Mg–6Zn–1Y and Mg–6Zn–3Y(wt%) alloys under different cooling rates were investigated. The results show that the second dendrite arm spacing(SDAS) of Mg–6Zn–1Y and Mg–6Zn–3Y is reduced by 32 and 30% with increasing cooling rates(Rc) from 10.2 to 23 K/s, which can be predicted using a empirical model of SDAS=68 R 0:45:45cand SDAS=73 R 0c, respectively. The compressive strength of both alloys increases with increasing the cooling rate, which is attributed to the increase of volume fraction(Vf) of secondary phases under high cooling rate. The interaction of the cooling rate and component with SDAS has been theoretically analyzed using interdependence theory.     

Effects of Zinc and Calcium Concentration on the Microstructure and Mechanical Properties of Hot-Rolled Mg–Zn–Ca Sheets

Four kinds of Mg alloys with different Zn and Ca concentration were selected to analyze the effect of Zn and Ca concentration on the microstructure and the mechanical properties of Mg–Zn–Ca alloys. It was found that Zn and Ca concentration has a great influence on the volume fraction, the morphology and the size of second phase. The Mg–1.95Zn–0.75Ca(wt%) alloy with the highest volume fraction, continuous network and largest size of Ca2Mg6Zn3 phase showed the lowest elongation to failure of about 7%, while the Mg–0.73Zn–0.12Ca(wt%) alloy with the lowest volume fraction and smallest size of Ca2Mg6Zn3 phase showed the highest elongation to failure of about 37%. It was suggested that uniform elongations of the Mg–Zn–Ca alloys were sensitive to the volume fraction of the Ca2Mg6Zn3 phases, especially the network Ca2Mg6Zn3phases; post-uniform elongations were dependent on the size of the Ca2Mg6Zn3 phase, especially the size of network Ca2Mg6Zn3 phase. Reduction in Zn and Ca concentration was an effective way to improve the roomtemperature ductility of weak textured Mg–Zn–Ca alloys.     

Preparation and properties of nano-CeO2/Zn composites

The nano-composite powders of CeO2/Zn were prepared with high energy ball milling and the nano-composite materials of CeO2/Zn were fabricated with vacuum sintering powder metallurgy. Meanwhile, the composite and structure were analyzed by the means of XRD and FESEM. From the comparison of different nano-CeO2 contents composites, the best corrosion resistance and hardness, and the optimum content of nano-CeO2 were achieved. The result shows that corrosion resistance, hardness and uniformity of metal structure can be improved significantly with nano-CeO2; at the same time, the optimal corrosion resistance, hardness and microstructure are obtained when the mass fraction of nano-CeO2 is 1%.     

Electrodeposition and properties of Zn,Zn–Ni,Zn–Fe and Zn–Fe–Ni alloys from acidic chloride–sulphate electrolytes

Abstract

Zn, Zn–Ni, Zn–Fe and Zn–Fe–Ni films have been deposited by electrochemical deposition technique onto steel plate substrates. The objective of this study was to characterise the corrosion properties of these alloys in saline solution for the application as new environmentally friendly sacrificial coatings in the protection of steel structures. The morphological and structural properties of the alloys were systematically studied using XRD and SEM techniques. Cyclic voltammetry of the individual metals was performed to help understand the electroplating process of the films. Grain sizes of the films were calculated using Scherrer's formula. Partial substitution of Zn to Fe and Ni leads to an improvement in the corrosion resistance. Compared with other zinc alloys, the Zn–Ni alloy deposit was the noblest.     

Influence of Zn Content on Microstructure and Tensile Properties of Mg–Zn–Y–Nd Alloy

In the present study, the effect of Zn content on the microstructure and deformation behavior of the as-cast Mg–Zn–Y–Nd alloy has been investigated. The results showed that as Zn content increased, the volume fraction of secondary phases increased. Moreover, the phase transformation from W-phase to W-phase and I-phase occurred. In the as-cast state,W-phase exists as eutectic and large block form. When Zn content increases to 6 and 8%(wt%), small I-phase could precipitate around W-phase particles. Additionally, the effect of Zn content on the tensile properties and deformation behavior varies with the testing temperature. At room temperature, the tensile strength increases with Zn content, whereas the elongation increases initially and then decreases. At 250 °C, as Zn content increases, the tensile strength decreases initially and then increases slightly, whereas the elongation decreases. At 350 °C, the elongation increases with Zn content,whereas the tensile strength decreases initially and then increases slightly.     

Hot deformation behavior of Al-Cu-Li-Mg-Zr alloy containing Zn and Mn

The hot deformation behavior of a new AI-Cu-Li-Mg-Zr alloy was studied, and its microstructure and true stress were characterized as function of the deformation temperature and the strain rate using Gleeble-1500 thermal mechanical simulator. The results show that, with the increase of the strain rate from 0.001 s^-1 to 10 s^-1, the peak value of true stress is elevated at the same deformation temperature, and at the same strain rate the peak value of the true stress decreases with the increase of the deformation temperature from 360 ℃ to 520℃. Dynamic recrystallization easily occurs in the new Al-Cu-Li-Mg-Zr alloy under the lower strain rate and the higher deformation temperature, and dynamic recovery can usually be seen in this alloy under the higher strain rate of 10 s^-1 and the lower deformation temperature.     

Effect of cooling and aging on microstructure and mechanical properties of Sn－9Zn solder

The microstructure and tensile properties of Sn-9Zn solder under different cooling and aging condition were studied.During solidification, the distribution of Zn-rich phases and grain size in the microstructure of Sn-9Zn solder were decided by the cooling rate.The Zn-rich phase in Sn-9Zn solder under furnace cooling, air cooling and water cooling media was separately existed as coarsen dendritic and needle like shape, fine needle like shape and very fine rod-like shape, respectively.After aging, the coarsen dendritic was broken and the coarsen needle like Zn-rich phase was partly changed into fine distribution of Zn-rich phase for Sn-9Zn solder with furnace cooling, and the rod-like Zn phase in the Sn-9Zn solder under water cooling was changed to conglomerated Zn with needle shape.During tensile testing on Sn-9Zn solder, tensile strength and ductility reached the best with water cooling, but decreased with aging effect.Meanwhile, the ductility of solder with air cooling and the strength of solder with furnace cooling increased with aging.The fracture mode was ductile and was independent of cooling media and aging effect.The size and depth of dimples decreased from water, furnace to air cooling.After aging, number and size of dimples increased on the solder with furnace cooling and air cooling.The change on the size of dimples for the Sn-9Zn solder under different cooling condition and with aging effect was accordance to the tensile properties.     

Effects of Zr and Y on the Mechanical Properties and the Microstructure of Ti-Al-Sn-Nb-Mo-Si Alloy

In the present paper the effects of additions of Zr and Y on the microstructure and mechanical properties for Ti-(6.06.5)Al-(2.0～3.0)Sn-(1.5～6.0)Zr-(0.8～1.0)Mo-1.0Nb-0.25Si alloys are reported,The experimental results show that: with in-creasing of Zr content,tensile strength and creep resistance of the alloys increase,and reduction in area and thermal stability ofthe alloys decrease.Decrease in thermal stabiIity of the alloys mainly caused by surface thermal unstability.After heat treatmentY addition can make grain size of the alloys refine.The reduction in area and thermal stability of the alloys with Y addition areimproved,and tensile strength slightly decreases and creep resistance is essentially the same as the alloy without Y addition.Thesephenomena are explained in brief.     

High-strain-rate superplasticity of the Al–Zn–Mg–Cu alloys with Fe and Ni additions

During high-strain-rate superplastic deformation, superplasticity indices, and the microstructure of two Al–Zn–Mg–Cu–Zr alloys with additions of nickel and iron, which contain equal volume fractions of eutectic particles of Al₃Ni or Al₉FeNi, have been compared. It has been shown that the alloys exhibit superplasticity with 300–800% elongations at the strain rates of 1 × 10^–2–1 × 10^–1 s^–1. The differences in the kinetics of alloy recrystallization in the course of heating and deformation at different temperatures and rates of the superplastic deformation, which are related to the various parameters of the particles of the eutectic phases, have been found. At strain rates higher than 4 × 10^–2, in the alloy with Fe and Ni, a partially nonrecrystallized structure is retained up to material failure and, in the alloy with Ni, a completely recrystallized structure is formed at rates of up to 1 × 10^–1 s^–1.     

Precipitate characteristics and their effect on the prismatic-slip-dominated deformation behaviour of an Mg–6 Zn alloy

This study provides a detailed quantitative characterization of precipitation in an Mg–6 Zn alloy. Transmission electron microscopy (TEM) was used to characterize the average size, aspect ratio and volume fraction of the rod-shaped precipitates for ageing at 200 °C. The effect of these precipitate characteristics on the prismatic-slip-dominated deformation behaviour of the above alloy has been evaluated. In particular, their effect on the yield strength and work hardening behaviour of the alloy has been determined. The potential role of Zn solute in solution on the rate of dynamic recovery is discussed. TEM was also used to examine the precipitate–dislocation interaction mechanism on the prism plane in various precipitation states. It was found that the Orowan equation is appropriate for predicting the strengthening on the prism and basal planes due to rod-shaped precipitates.     

Synergistic inhibition effect of poly(ethylene glycol) and cetyltrimethylammonium bromide on corrosion of Zn and Zn—Ni alloys for alkaline batteries

The synergistic inhibition effect of poly(ethylene glycol)-400 (PEG-400) and cetyltrimethylammonium bromide (CTMAB) on the corrosion of Zn and Zn—Ni alloys in 8 mol/L KOH solution saturated with ZnO was observed by potentiodynamic anodic/cathodic polarization (PDP), and electrochemical impedance spectroscopy (EIS) measurements. The electrochemical studies confirmed that there was a synergism between PEG-400 and CTMAB on corrosion inhibition of Zn and its alloys. Corrosion inhibition efficiency of the mixed inhibitors, 250 mg/L CTMAB + 250 mg/L PEG-400, was found to be much higher than that of the single inhibitor, 500 mg/L PEG-400 or 500 mg/L CTMAB. Scanning electron microscopic (SEM) investigations before and after the corrosion inhibition process emphasize the synergistic effect of the mixed inhibitors. Accordingly, it was found that the addition of the investigated inhibitors to the alkaline solution enhanced the discharge and capacity of the alkaline battery anodes. The obtained electrochemical data exhibited a good correlation with the computational one.     

Effect of addition of Zn and Al elements on glass-forming ability and thermal stability of Mg-Cu-Y bulk metallic glasses

After substituting partial Cu and Mg with Zn or Al elements for Mg65Cu25Y10 alloy, respectively, the metallic glass plate samples with thickness of 2-3 mm were prepared by water-quenching, their respective glass-forming ability and thermal stability were studied by using differential thermal analysis （DTA） and X-ray diffraction （XRD）. Using Kissinger equation, the activation energies of crystallization of these metallic glasses heated with a constant rate were calculated. The results show that Al element is greatly harmful to the glass-forming ability of Mg-Cu-Y alloys and cannot acquire bulk amorphous alloys; nevertheless, the effect of Zn element addition is indeterminate for various components. The magnitudes of thermal stability are also revealed.     

Evolution of precipitate microstructures during the retrogression and re-ageing heat treatment of an Al–Zn–Mg–Cu alloy

Using a combination of experimental techniques, including anomalous small-angle scattering and atom-probe tomography, the evolution of precipitate microstructures during the different steps of retrogression and re-ageing (RRA) heat treatments of an Al–Zn–Mg–Cu alloy has been systematically evaluated. Quantitative information on the morphology, scale and chemistry of the precipitates provide new insight into the mechanisms at work during this process. It is shown that both the final chemistry and precipitate size distribution are different in the final RRA temper compared to classical heat treatments, with the presence of small clusters nucleated during the re-ageing step, and an average precipitate composition richer in Cu, together with a matrix enrichment in Zn, related to the difference in diffusivity between the two solute atoms. The mechanisms of precipitate evolution during the reversion and re-ageing steps are discussed in light of the influence of the process parameters.     

Adsorption difference of Pb2＋ and Zn2＋ in sandstone and breccia

The adsorption difference of Pb2 and Zn2 in sandstone and breccia of Pb-Zn Mine of Yunnan Province was studied by using modem instrument analysis method and fractal geometry theory. The results show that the adsorption capacity (Q) of Pb2 in this two rocks is bigger than that of Zn2 , and Q in various initial concentration solutions obeysv Freundlich experiential formula. The value of l/n on the adsorption Pb2 and Zn2 in sandstone hardly has any difference, but the value ofk differs observably. The adsorption process ofZn2 or Pb2 in sandstone or breccia from solution is fractal-like. The kinetic equation of adsorption is lgp = k - alg t or Q = abt( 1 bt)-1, and the values oflg k, a, and D of brecciaare bigger than those of sandstone at 30 and 50 ℃. These parameters decrease basically with the increase of temperature.The adsorption capacity of Pb2 is almost equal in sandstone and breccia, but the adsorption ability of Zn2 in breccia is stronger than that in sandstone.