Direct current electrodeposition of Zn and Zn–SiC nanocomposite coatings

Pure Zn and Zn matrix composite coatings containing nano-sized SiC particles with an average size of 50 nm were prepared from the zinc sulphate bath. The effect of the particle concentration and current density on the amount of particles embedded was examined. Electron microscopic studies revealed that the coating morphology was modified by the presence of SiC nanoparticles. Corrosion resistance properties of the coatings were studied using a potentiodynamic polarisation technique in 1M NaCl solution. It was established that agglomeration of nanoparticles worsens corrosion resistance properties of Zn–SiC coatings. However, the presence of well dispersed nanoparticles significantly improves the corrosion resistance of the zinc. Incorporation of SiC nanoparticles also improves the microhardness of the zinc matrix.     

Dependency of the thermal and electrical conductivity on temperatures and compositions of Zn in the Al−Zn alloys

The variations of thermal conductivity (K) with temperature for Al–xZn (x = 5, 10, 20, 30, 50 and 60 wt. %) alloys were measured by using a radial heat flow furnace. The variations of electrical conductivity (σ) of solid phases with temperature for the studied alloys were determined from the Wiedemann-Franz and Smith-Palmer equations by using the measured values of K from the plots of K. The thermal temperature coefficient (α_TTC) and the electrical temperature coefficient (α_ETC) were obtained. Dependency of the α_TTC and α_ETC on the composition of Zn in the Al?Zn alloys was also investigated. According to the present experimental results, K of Al–Zn alloys linearly decrease with increasing temperatures up to the melting temperature for each composition and exponentially decrease with the increasing Zn content. On the other hand, the σ of Al based Al-Zn alloys exponentially decrease with increasing temperature and Zn content.     

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.     

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.     

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.     

Mechanical alloying and subsequent heat treatment of Ag–Zn powders

Microstructural evolution during mechanical alloying of Ag and Zn, and subsequent heat treatments were investigated. The mechanical alloying was carried out in a SPEX 8000D miller. The microstructural characterization was obtained by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The thermal behavior was studied using differential scanning calorimetry (DSC). Based on the results obtained, it can be concluded that at the early stages of milling was possible to detect the ?, β, β′, α solid solutions and remaining Zn. Later, the ?, β, β′ and Zn phases disappeared while the Zn concentration of the α solid solution was strongly increased. After 7.2 ks of milling, the mechanical alloying process reached a steady state. During this period, both the composition and crystallite size of the α solid solution remained practically unchanged. On the other hand, subsequent heat treatments of milled powders showed that the α solid solution could also be obtained by the combination of mechanical alloying and heat treatment. Finally, the evolution of the microstructure during milling and annealing was combined to propose an optimal processing route in order to obtain a α solid solution.     

Comparison of photocatalytic activity of TiO2 film doped nonuniformly by Mn and Zn

1INTRODUCTIONHeterogeneous photocatalysis attracts muchattention as a friendly environment technique valu-able for water and air purification.However,thereare some problems in application,and one of thekey problems is the low photon-quantum efficien-cy.From1990s,the modification of Ti O2by metalions has become a hot topic,andthe effect of metal(such as Cu,Fe,Ag,Au,Pt,W,V,Pb,Cr,Rh,Co and Ni)ions doping on photocatalytic ac-tivity of Ti O2has been studied widely[14].Howev-er,there wer…     

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.     

Tensile properties and strengthening mechanisms of Mg−Zn−Zr alloys

Six Mg−Zn−Zr alloys, with and without RE additionswere tested at room temperature and 473 K. Yield stresses of parts of the six alloys were calculated theoretically. Microstructures of the specimens before and after heat treatment were compared in order to determine the reason for the decrease in yield stresses at room temperature. The strengthening mechanisms at different temperatures were discussed. This article is based on a presentation in “The 7th Korea-China Workshop on Advanced Materials” organized by the Korea-China Advanced Materials Cooperation Center and the China-Korea Advanced Materials Cooperation Center, held at Ramada Plaza Jeju Hotel, Jeju Island, Korea on August 24–27, 2003.     

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.     

Anti-Corrosion and Tribo-Mechanical Properties of Co-deposited Zn–SnO_2 Composite Coating

Zn–Sn O2 composite coatings were prepared by direct potential using electrolytic co-deposition technique from sulfate solution.The effect of Zn2?and Sn O2 concentrations in deposited bath on the mechanical properties and morphological characteristics of the composite coatings were examined.The characterizations of the sample were analyzed using scanning electron microscopy couple with energy dispersive spectroscopy(SEM/EDS),X-ray diffraction(XRD) and atomic force microscopy(AFM).The electrochemical degradation behavior of the samples in 3.65 wt.% Na Cl solution was studied using potentiodynamic polarization technique and characterized by high-resolution optical microscope.From all the fabricated composite coatings,obvious diffraction peaks were observed with Zn-7Sn-S-0.3V film with Zn2Sn7,Sn,Zn2Sn5 and Zn phases,confirming the presence and formation of Zn–Sn O2 coating.The XRD pattern shows that the presences of Sn O2 particle remarkably play a major role in the precipitation and orientation of the alloy matrix.From the SEM/EDS and AFM results,the deposits show that composite particle and proper bath composition have strong influence on the microstructure.An enhanced corrosion resistance was attained as a result of the induced particles.     

Influence of crystal structure and formation energies of impurities （Mg, Zn and Ca） in zinc blende GaN

First-principles calculations on neutral metal impurities （Mg, Zn and Ca） in zinc blende GaN were studied. Formation energies were calculated for substitution on the gallium site, the nitrogen site and incorporation in the octahedral interstitial site and the tetrahedral interstitial sites. The calculated results show that the major defects studied have a high formation energy in excess of 5 eV, and the gallium substitutional site is favorable for incorporation. MgGa has particularly low formation energy 1.19 eV and can be expected to incorporate readily into GaN. The local crystal structural changes around the impurity in the lattice were studied after metal atoms occupying the gallium substitutional site. It shows that the lattice constant becomes bigger and the tetrahedral angle between impurities and its nearest N atom becomes smaller mainly due to the extended M-N bond length and big size of impurities atoms, which results in a local lattice distortion. The Zn-N （2.04 A） bond strength is the smallest among the three impurities which raises the formation energy. CaGa is unfavorable due to a large size mismatch in spite of a large bond strength （2.25 A）. The calculated results identify the two key factors determining impurities incorporation in zinc blende GaN： the atomic size of impurities comparing to that of host atoms and the bond strength between the impurities and its neighbors. The results are in well agreement with other calculated and experimental results.     

Effect of spray forming on evolution of microstructure and mechanical behavior of Mg-9Al-1Zn alloy

The cylindrical billet of Mg-9Al-1Zn alloy was produced by spray forming and hot extruded at 698-723 K with an extrusion ratio of 22：1, The microstructural evolution was investigated systematically. The mechanisms of grain refinement, solubility extension of Al and Zn elements in Mg matrix, and the precipitation of the second phase β-Mg17Al12 as well as their effect on the mechanical properties of the Mg-9Al-1Zn alloy were analyzed and discussed. The results show that the spray formed Mg-9Al-1Zn alloy has homogeneous equiaxed fine grains with the average grain size of 17 μm, of which the average grain size is refined further to 5 μm due to dynamic recrystallization during hot extrusion process. The evolution of size, proportion and distribution offl-Mg17Al12 phase was also observed and analyzed. The mechanical properties for the extruded rods are improved remarkably at ambient temperature.     

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.     

Effect of Y addition on microstructure and mechanical properties of Mg–Zn–Mn alloy

The effects of Y on the microstructure and mechanical properties of Mg–6Zn–1Mn alloy were investigated. The results show that the addition of Y has significant effect on the phase composition, microstructure and mechanical properties of Mg–6Zn–1Mn alloy. Varied phases compositions, including Mg₇Zn₃, I-phase (Mg₃YZn₆), W-phase (Mg₃Y₂Zn₃) and X-phase (Mg₁₂YZn), are obtained by adjusting the Zn to Y mass ratio. Mn element exists as the fine Mn particles, which are well distributed in the alloy. Thermal analysis and microstructure observation reveal that the phase stability follows the trend of X>W>I>Mg₇Zn₃. In addition, Y can improve the mechanical properties of Mg–Zn–Mn alloy significantly, and the alloy with Y content of 6.09% has the best mechanical properties. The high strength is mainly due to the strengthening by the grain size refinement, dispersion strengthening by fine Mn particles, and introduction of the Mg–Zn–Y ternary phases.     

Effect of Al addition on microstructure and mechanical properties of Mg−Gd−Zn alloys

The microstructure evolution and mechanical properties of Mg?15.3Gd?1Zn alloys with different Al contents (0, 0.4, 0.7 and 1.0 wt.%) were investigated. Microstructural analysis indicates that the addition of 0.4 wt.% Al facilitates the formation of 18R-LPSO phase (Mg₁₂Gd(Al, Zn)) in the Mg?Gd?Zn alloy. The contents of Al₁₁Gd₃ and Al₂Gd increase with the increase of Al content, while the content of (Mg, Zn)₃Gd decreases. After homogenization treatment, (Mg, Zn)₃Gd, 18R-LPSO and some Al₁₁Gd₃ phases are transformed into the high-temperature stable 14H-LPSO phases. The particulate Al?Gd phases can stimulate the nucleation of dynamic recrystallization by the particle simulated nucleation (PSN) mechanism. The tensile strength of the as-rolled alloys is improved remarkably due to the grain refinement and the fiber-like reinforcement of LPSO phase. The precipitation of the β′ phase in the peak-aged alloys can significantly improve the strength. The peak-aged alloy containing 0.4 wt.% Al achieves excellent mechanical properties and the UTS, YS and elongation are 458 MPa, 375 MPa and 6.2%, respectively.