Al Zn System Research Articles

The ( α1 + α2) miscibility gap of the Al–Zn–Cu system at 360 °C

The effect of Cu addition on the ( α 1 + α 2 ) miscibility gap of the Al–Zn binary system was studied at 360 °C by using the diffusion couple technique. It was experimentally verified that the highest temperature of the ( α 1 + α 2 ) miscibility gap of the Al–Zn system is significantly increased by the addition of Cu. The miscibility gap of Al–Zn–Cu face-centered cubic solid solution becomes smaller with the addition of Zn than that of the Al–Cu binary system above 351 °C, which is in agreement with previous thermodynamic predictions.

Recycling from Mg–Al–Zn system alloy to the high-purity Mg–Zn alloy by the vacuum distillation method

Machined chips of the Mg–Al–Zn alloy were converted to a raw material, and the recycling from Mg–Al–Zn system alloys to high-purity Mg–Zn alloys by the vacuum distillation method was examined. For 100 g of raw material AZ31 magnesium base alloy machined chips, a raw material temperature of 600°C, a condenser temperature of 355°C, and a purification time 7 h, the evaporation ratio is nearly 95%. The condenser condensate becomes about 93%, and Mg and Zn in the raw material can be almost completely recovered in the condenser as high purity Mg–Zn alloy that is free of impurities such as Fe, Ni and Cu. The corrosion rate of recycling extrusions became a little worse in comparison with about 0.5 mm/y for 4 N magnesium extrusion samples, and the corrosion resistance became better than that of AZ91D magnesium base alloy die castings. The recycling extrusions was elongated a little less in comparison with the 4 N magnesium extrusions, and the tensile strength and the 0.2% proof stress increased to about 50 MPa.

The Role of Zirconium Additions in Recrystallization of Aluminum Alloys

Control of grain size during recrystallization of aluminum alloys is critical when tailoring material properties for structural applications. Most commonly the grain size is controlled by adding alloying elements which form second phases during homogenization heat treatments small enough to impose a Zener drag on the grain boundary mobility. These phases are known as dispersoids and are in the 10 to 200 nm in diameter range. In Al-Zn alloys, zirconium has been successfully used in controlling the degree of recrystallization after solution heat treatments. It is commonly understood that the Al3Zr dispersoids of about 20 nm in diameter present in the microstructure are the key features affecting grain boundary mobility. With the success of controlling recrystallization in Al- Zn alloys, zirconium has been added to other alloy systems, such as Al-Cu-Mn, and a similar retarding effect in recrystallization kinetics has been observed as seen in the Al-Zn systems. However, in Al-Cu-Mn alloys, zirconium bearing dispersoids are not observable in the microstructure. Consequently, additional microstructural effects such as solute drag need to be considered to explain the experimental observations. In this paper, the role of zirconium additions in aluminum alloys will be summarized.

Electrochemical investigation of the passive behaviour of biomaterials based on Ag–Sn and Cu–Zn–Al in carbonate buffer in the absence and presence of chloride

The electrochemical behaviour of biomaterials based on Cu–Zn–Al (cubic Cu3Zn phase) and Ag–Sn (orthorhombic Ag3Sn and hexagonal Ag4Sn phases) alloys was investigated in carbonate buffer solutions (pH 9.66) in the absence and presence of chloride, using different electrochemical techniques. Analyses of the open circuit potential and the potentiodynamic polarisation curves showed that the passivation domain and the corrosion parameters depend on alloy composition and chloride concentration. Chronoamperometric studies showed that passivation kinetics and corrosion of the passive film are both well described by a linear ln(i) versus ln(t) relation. The passive film formed on the Ag–Sn alloy is less susceptible to corrosion when compared to the Cu–Zn–Al system. The impedance data obtained in the passive region for the Cu–Zn–Al alloy showed that the passive layer is compact. In contrast, the impedance data obtained for the Ag–Sn alloy showed that the passive layer is formed by a compact oxide layer covered by a porous oxide gel layer. Mott–Schottky analysis showed that the passive film formed on the Cu–Zn–Al alloy behaves as a p-type semiconductor.

Ternary phases in the Yb–Zn–Al system with La 3Al 11- and Yb 8Cu 17Al 49-type structures

Several compounds with La 3Al 11- and Yb 8Cu 17Al 49-type structures were synthesized in the ternary Yb–Zn–Al system and their crystal structure and existence range were determined by both single-crystal and powder methods. For two of them, crystallizing with the La 3Al 11-type, orthorhombic, Immm, o/28, refinement was made by single-crystal data: Yb 3Zn 6.16Al 4.84, a = 428.95(4) pm, b = 975.5(1) pm, c = 1257.3(2) pm, wR2 = 0.052; Yb 3Zn 4.84Al 6.16, a = 427.03(5) pm, b = 988.6(1) pm, c = 1249.5(2) pm, wR2 = 0.104. Though zinc and aluminium share the same sites, some preferential occupation is recognizable. This phase forms between 35 and 50 at% Al. On the Zn-rich side, starting from binary Yb 3Zn 11, a replacement of ∼3 at% Al for Zn is reached, then a heterogeneity range appears. Two other phases, crystallizing with the Yb 8Cu 17Al 49-type, tetragonal, I4/ mmm, tI74, were determined by single-crystal methods: Yb 8Zn 48.5Al 17.5, a = 874.6(2) pm, c = 1615.8(3) pm, wR2 = 0.055; Yb 8Zn 41.4Al 24.6, a = 869.5(3) pm, c = 1637.1(7) pm, wR2 = 0.104. The structure of these latter compounds can be related to the Th 6Mn 23 type. A common building unit is found and several coordination polyhedra show similar features. Two atomic sites with zinc only and four with Zn/Al mixtures are filled.

Intercalation behavior of l-ascorbic acid into layered double hydroxides

The intercalation of l-ascorbic acid (ASA) into three kinds of layered double hydroxides, such as Mg–Al, Mg–Fe and Zn–Al LDHs, has quantitatively been investigated by the calcination-rehydration (reconstruction) and coprecipitation methods. The amount of ASA intercalated was considerably different by the LDH systems that was estimated to be ca. 0.40 mol/mol-M 3+ for the Mg–Al and Mg–Fe systems by the reconstruction method. The Zn–Al system was hardly restored to the LDH structure by the rehydration reaction with the intercalation of ASA. ASA was also intercalated into the Mg–Al and Zn–Al LDHs by the coprecipitation method, while the intercalation of NO 3 − was observed in the Mg–Fe LDH. The basal spacing of the solid products were expanded to d 003 = 0.84 (Mg–Al) and 0.86 (Mg–Fe) nm by the reconstruction method, 0.97 (Mg–Al) and 1.06 (Zn–Al) nm by the coprecipitation method, respectively, suggesting that ASA was intercalated into the LDHs. A large fraction of ASA was intercalated as reduced form after the light and heat resistance tests of the ASA/LDHs. This result confirmed that ASA was stabilized by the intercalation of the LDHs interlayer space. Furthermore, the intercalated ASA was easily deintercalated from the LDH interlayer space by the ion exchange method using CO 3 2−. It is expected that LDHs will be good host materials for safe storage of vitamins.

Electrical, magnetic, thermal and thermoelectric properties of the “Bergman phase” Mg 32(Al,Zn) 49 complex metallic alloy

The Mg–Al–Zn system of intermetallics contains an exceptional crystalline phase Mg 32(Al,Zn) 49, named the Bergman phase, whose crystal structure is based on a periodic arrangement of icosahedral Bergman clusters within the giant-unit-cell, so that periodic and quasiperiodic atomic orders compete in determining the physical properties of the material. We have investigated electrical, magnetic, thermal and thermoelectric properties of a monocrystalline Bergman phase sample of composition Mg 29.4(Al,Zn) 51.6, grown by the Bridgman technique. Electrical resistivity is in the range ρ ≈ 40 μΩ cm and exhibits positive-temperature-coefficient with T 2 dependence at low temperatures and T at higher temperatures, resembling non-magnetic amorphous alloys. Magnetic susceptibility χ measurements revealed that the sample is a Pauli paramagnet with a significant Landau diamagnetic orbital contribution. The susceptibility exhibits a weak increase towards higher temperature. Combined analysis of the ρ( T) and χ( T), together with the independent determination of the Pauli susceptibility via the NMR Knight shift suggests that the observed temperature dependence originates from the mean-free-path effect on the orbital susceptibility. The electronic density of states (DOS) at the Fermi energy E F was estimated by NMR and was found to amount 72% of the DOS of the fcc Al metal, with no evidence on the existence of a pseudogap. Thermal conductivity contains electronic, Debye and hopping of localized vibrations terms, whereas thermopower is small and negative. High structural complexity of the Bergman phase does not result in high complexity of its electronic structure.

Microscopic structures of Laves phases and structurally related compounds: a transmission electron microscopy study

Abstract We present microstructural investigations of Laves phases AB2 and structurally related compounds using transmission electron microscopy. Convergent-beam electron diffration in combination with selected-area diffraction has been used to determine uniquely the space group symmetry of the respective phases from very small illuminated regions. In addition stacking faults, domain boundaries, and intergrowth have been studied by HREM images. By electron beam irradiation intermetallic phases have been transformed in-situ into phases of different compositions. Polar intermetallic phases in the systems Ca—Al—Zn, Ba—Al and Ba—Al—Zn, as well as transition metal based Nb-Co phases have been chosen for this case study. In the Ca—Al—Zn system, the C15- and C36-type crystals did not show orderliness but a randomly mixed occupation of the B-net by Al and Zn atoms. Starting from C36, a C15 phase of constant Ca and lower Zn content as well as a new C36 phase with higher Ca content could be synthesized by means of electron beam irradiation. In the case of CaAlZn no ordering of Al and Zn were observed, i.e., Al and Zn randomly mixed occupy the Cu-site in the CeCu2 structure type. By electron beam irradiation of CaAlZn, a novel hexagonal phase with a hitherto unknown crystal structure is formed. The crystal structures of Ba21Al40 and Ba14Al22+xZn5–x are derived from Laves-type structures by omitting and modifying some of the triangular and Kagom, layers. In the case of Ba21Al40, intergrowth of motifs from the crystal structures of Ba3Al5 and Ba4Al5 were observed, whereas for Ba14Al22+xZn5–x the bulk phase displays a domain structure. Adjacent domains are misoriented by ∼120°, the specific angle resulting from the pseudo-trigonal symmetry of the Ba-net. Therefore, only the (Al,Zn)-net is disordered. No superstructure formation were detected for the three polytypes C36, C15 and C14 in the Nb—Co system. However, TEM images of C36-Nb1–xCo2+x reveal a high stacking fault density with intergrowth of stacks of C36 and C15 sequence. When the C15 phase is rich in Nb, stacking faults seem to be more important than for Co-rich C15 phases, whereas stacking faults have seldom been observed for the Co-rich C14 phase.

Yb–Zn–Al ternary system: CaCu 5-type derived compounds in the zinc-rich corner

As part of a study of the Yb–Zn–Al system, this first article reports the synthesis and crystal structure of four compounds. The crystal structures were determined by single crystal diffractometer data for three of them: Yb 3.36Zn 30.94Al 4.34, hexagonal, P6/ mmm, a = 9.061 ( 2 ) Å , c = 8.878 ( 2 ) Å , Z = 1 , w R 2 = 0.055 , with a structure derived from the SmZn 11∼ type; Yb 6.4Zn 46.8Al 3.4, hexagonal, P6/ mmm, a = 9.096 ( 3 ) Å , c = 13.178 ( 5 ) Å , Z = 1 , w R 2 = 0.060 , with its own structure; Yb 12.4Zn 96.8Al 4.4, hexagonal, P6 3/ mmc, a = 9.068 ( 2 ) Å , c = 26.369 ( 8 ) Å , Z = 1 , w R 2 = 0.088 , with a structure derived from the U 2Zn 17 type. The structure of Yb 3Zn 17.7Al 4.3, tetragonal, I4 1/ amd, a = 8.920 ( 1 ) Å , c = 21.294 ( 1 ) Å , Z = 4 , related to the Ce 3Zn 22 type, was refined from powder data by the Rietveld method. The four structures belong to the same family, derived from the CaCu 5 type by replacing totally or partially some Ca atoms with dumbbells of partner elements. All the structures show no order for the aluminium atoms, but they preferentially occupy the dumbbells sharing the sites with zinc.

Phase equilibria and solidification of Mg-rich Mg–Al–Zn alloys

Phase equilibria in Mg-rich corner of Mg–Al–Zn system are analyzed in detail. Thermodynamic calculations are compared with literature data and own key experimental results by means of DSC and DTA measurements. The detailed comparison strongly supports the reliability of the selected thermodynamic description. Furthermore, our focus is placed on proper interpretation of experimental results obtained by thermal analysis. Based on thermodynamic calculation, it is clarified that a signal observed in thermal analysis, which was interpreted as end of solidification in the literature, is related to the start of the monovariant eutectic reaction L + (Mg) + γ-Mg 17Al 12 under non-equilibrium condition and the solidification process ends at lower temperature. This fact is supported by our microstructural observation.

Surface segregation and surface tension in Al–Sn–Zn liquid alloys

A new expression for the surface tension ( σ ) of ternary liquid alloys has been developed in terms of surface composition and similarity coefficients ( ξ ij ) which takes into account the correlation between the component atoms of the system. The expression involves the same ordering energies for the concerned binaries as used for its bulk and surface calculations and bulk calculation of the ternary system. Our theoretical investigation successfully reproduced the experimental findings for all concerned binaries of the Al–Sn–Zn system. The surface is quite enriched with Sn atoms in the Sn–Zn and Al–Sn systems while the Al–Zn system exhibits segregation of Zn atoms at the surface. σ decreases with Sn concentration in both Sn–Zn and Al–Sn systems. In the Al–Zn system it decreases with the increase of Zn content. In the Al–Sn–Zn system a slight decrease in σ is observed. σ -is almost the same up to 20% aluminium in the three cross-sections of Sn and Zn, i.e. 1:1, 1:2 and 2:1. σ increases beyond this concentration in all cross-sections. The surface is quite enriched with Sn atoms—the maximum being at the 2:1 and the minimum at the 1:2 cross-section.

Correlation between CALPHAD data and the Cahn–Hilliard gradient energy coefficient [formula omitted] and exploration into its composition dependence

Expressions for the Cahn–Hilliard gradient energy coefficient κ for a binary, face-centered cubic crystal are derived by consideration of pair-wise, three-body, and four-body nearest-neighbor interactions. The resulting equations are expressed in terms of the interaction energies of clusters of atoms, and are related to bulk thermodynamic data available in CALPHAD databases. The three- and four-body interactions introduce a composition dependence into the expressions for κ . Values of κ calculated for the Al–Zn system are in good agreement with those reported elsewhere. Equilibrium composition profiles and interfacial energies are calculated using each approximation.

An application of the molar Gibbs energy diagrams for determining the composition of a growing phase and of its rate of growth

A method for estimating the composition of a growing phase and the growth rate is proposed. The essence of the method is clarified (graphically) by using the molar Gibbs energy diagrams. The workability of the method is illustrated by applying it to the Al–Zn system.

7xxx계 Al 혼합분말의 승온속도에 따른 소결거동

7xxx series Al alloy has the most attractive properties including its excellent high specific strength, stress corrosion cracking and corrosion-resistance. However, in case of the Al-Zn system, the liquid phase has a transient aspect because of the high solid solubility of Zn in Al. Therefore, transient liquid phase sintering behavior was observed during the sintering process. And the amount of liquid and its duration were influenced by the process variables including heating rate and final sintering temperature. At high heating rates(<TEX>$100^{\circ}C/min$</TEX>), the liquid fraction increased during sintering because diffusion was minimized and therefore local saturation could easily occur. The sintered density increased with increasing heating rate.

Microstructure and Mechanical Properties of a Rheo-Diecast Mg&amp;ndash;10Zn&amp;ndash;4.5Al Alloy

High zinc content Mg–Zn–Al alloys have the potential to be used as high pressure die casting (HPDC) alloys for applications up to 150C. However, these alloys show high tendency to hot tearing and microporosity. Rheo-diecasting (RDC) is an innovative semisolid HPDC process, which can effectively eliminate the formation of primary magnesium dendrites and convert them into fine, globular particles. This very positive change in the morphology and distribution of the primary phase reduces the subsequent formation of various casting defects. In this study, a composition of Mg–10Zn–4.5Al was selected from the Mg–Zn–Al system and processed with both HPDC and RDC. It is shown that, samples produced by the RDC process exhibit substantially reduced hot cracks, few gas pores, and a nearly uniform distribution of fine, globular primary particles. These microstructural changes resulted in much improved strength and elongation, which are comparable to those of AZ91D, while the processing temperature is much lower. It is concluded that high zinc content Mg–Zn–Al alloys have good potential to be exploited as commercially useful alloys by the RDC process.

Effect of ternary additions on the structure and properties of coatings produced by a high aluminum galvanizing bath

A zinc-aluminum eutectoid galvanized steel has been developed. The basic composition of the bath is selected close to the eutectoid point in the binary Zn—Al system, together with ternary additions in the form of bismuth, rare-earths and silicon.

Synthesis by ball milling and characterization of Al-Zn alloys

Mechanical ball milling is a useful technique for systems with positive enthalpy of mixing. With this technique solubility of a solute in a solid solution can be enhanced. Al-Zn system has positive heat of mixing. High energy ball milling has been employed to produce four alloys of Al with 2.5 to 10 wt% Zn. Powders of Al (1–125 μm) and Zn (0.7–5.0 μm) were mixed together in the desired proportion and milled with a powder to ball weight ratio of 1:20. The size and shape of the particles of as-received and alloy powders were examined in a scanning electron microscope (SEM) while their microanalysis was performed by energy dispersive system (EDS) attached with SEM. It has been observed that 120 h of milling of the powders produced homogeneous alloys. X-ray diffraction (XRD) patterns confirm complete solubility up to 10 wt% Zn in Al. Using the quasi-chemical theory of binary solid solutions, the enthalpy of mixing of 10 wt% Zn in Al has been determined to be 276 cals/mol. It is shown that stress exerted by very high density of dislocations, generated by mechanical milling, plays a major role in the enhancement of solubility. Hardness has been measured and it increases with increasing solute content.

Effect of Cu addition on the α1+ α2 miscibility gap of the Al–Zn system

The effect of the Cu addition on the ( α 1+ α 2) miscibility gap of the Al–Zn binary system was studied by using diffusion couple technique. The Zn concentrations in both α 1 and α 2 phases are decreased due to the small addition of Cu, and the Cu element is enriched in the α 2 phase, resulting in both α 1/( α 1+ α 2) and ( α 1+ α 2)/ α 2 phase boundaries of the miscibility gap shifting to the Al-rich corner in the Al–Zn–Cu ternary system.

Ｍｇ‐Ａｌ‐Ｚｎ系合金の押出性に及ぼす亜鉛およびマンガンの影響

The effects of zinc and manganese content on extrudability of Mg–Al–Zn system alloys have investigated. Zinc enhanced occurrence of surface cracks. Hence,as the zinc content increased, the extrusion speed limit became low. When the manganese and zinc content was high, the surface oxide film was thick and the surface color of the extrusion was black. On the other hand, manganese had the effect of increasing the tensile strength, 0.2% proof stress and elongation. Manganese enhanced the dynamic recrystalization in the extrusion process. As the result, the grain size of the extrusion was small.

Ba 14Zn 5− xAl 22+ x: a new polar intermetallic compound with a novel 2D network

A new ternary, intermetallic compound, Ba 14Zn 5− x Al 22+ x , was synthesized by heating the pure elements at 900°C. This compound crystallizes in the monoclinic space group I2/ m, Z=2, with a=10.474(2) Å, b=6.0834(14) Å, c=34.697(8) Å and β=90.814(4)°. The crystal structure of Ba 14Zn 5− x Al 22+ x consists of [Zn 5− x Al 22+ x ] slabs that are built with a novel, two-dimensional (2D) network of Zn and Al atoms involving eight-membered rings sandwiched between two layers of trigonal bipyramids interconnected by three-center bonding. Tight-binding, linear muffin–tin orbital (TB-LMTO-ASA) calculations have been performed to understand the relationship between composition and orbital interactions in the electronegative element framework. This new structure is closely related to the high-pressure, cubic Laves-type structure of BaAl 2 as well as the ambient pressure binary compound, Ba 7Al 13. The degree of valence electron charge transfer from the electropositive Ba atoms is related to the Al:Ba molar ratio in the Ba–Zn–Al system.