Binary Aluminum Alloys Research Articles

Rolling Texture Development in Aluminum-Zinc Solid Solutions

Rolling textures in face-centered cubic polycrystalline metals tend to transform from so-called pure metal to alloy textures with increasing stacking fault energy, so deformation texture correlates directly to stacking fault energy. As a 30th anniversary tribute to the classic copper-brass study by Hirsch and Lücke [1988], we recast the problem for binary aluminium alloys with 1, 10, 34 and 62wt.%Zn. Zinc (Zn) has a very high solid solubility in Al of up to 65at.% at 381°C, but at lower temperatures the Zn solid solution is unstable and can precipitate out or decompose spinodally. Current understanding is that Zn has no effect on the stacking fault energy of aluminum, so a priori, rolling of different Al-xZn alloys should result in no variation in deformation texture. Cast ingots were solutionized and promptly rolled 75 and 90% by multiple passes. X-ray texture pole figures were measured at the mid-plane of the rolled sheet, and the texture components calculated from the crystallographic orientation distribution function. Results show a decrease in {112}<11-1> and increase in {011}<21-1> with Zn content but uncorrelated changes in {123}<63-4> components. Bird’s eye - like microstructural features observed in the high Zn containing alloys at 90% reduction were {011}<21-1> and resemble those observed by other researchers in severely rolled brass, Al-4.5Mg and 316L.

Different Techniques of Determination of the Cracking Criterion for Solidification in Casting

Cracking which occurs during the solidification process is a serious defect in castings and welds. Alloys are susceptible to cracking during solidification. Al alloys, stainless steels and Ni-base alloys are notable examples. Cracking takes place in the semisolid region called the mushy zone. During solidification, shrinkage and thermal contraction of the mushy zone and its surrounding solid are hindered, tensile deformation can induce cracking (in the semisolid region) along grain boundaries that are not fed with sufficient liquid phase. The cracking criterion is focused on events occurring at the grain boundary, including separation of grains from each other, lateral growth of grains toward each other, and liquid feeding between grains. The susceptibility factor of a binary aluminum alloy to cracking during solidification was also described. The criterion has an effect upon: (a) the lateral growth rate of two neighboring grains toward each other to bond together to resist cracking, and (b) the length of the grain-boundary liquid channel through which feeding has to occur to resist cracking. In future work the criterion will be compared with experimental data and computer simulation during solidification of binary aluminum alloys in welding.

Deformation of nanocrystalline binary aluminum alloys with segregation of Mg, Co and Ti at grain boundaries

The influence of the temperature and sort of alloying element on the deformation of the nanocrystalline (NC) binary Al alloys with segregation of 10.2 at % Ti, Co, or Mg over grain boundaries has been studied using the molecular dynamics. The deformation behavior of the materials has been studied in detail by the simulation of the shear deformation of various Al bicrystals with the grain-boundary segregation of impurity atoms, namely, Ti, Co, or Mg. The deformation of bicrystals with different grain orientation has been studied. It has been found that Co introduction into grain boundaries of NC Al has a strengthening effect due to the deceleration of the grain-boundary migration (GBM) and difficulty in the grain-boundary sliding (GBS). The Mg segregation at the boundaries greatly impedes the GBM, but stimulates the development of the GBS. In the NC alloy of Al–Ti, the GBM occurs actively, and the flow-stress values are close to the values characteristic of pure Al.

Crack susceptibility of binary aluminum alloys during solidification

Cracking can occur during solidification in welding and casting. The present study attempted to deal with some fundamental questions regarding the susceptibility to cracking during solidification. How does the phase diagram affect the crack susceptibility? Can back diffusion occur in welding? How is the dihedral angle related to bridging between grains? To help answer the questions, the maximum |dT/d(fS)1/2| (T is temperature and fS fraction solid) was calculated, whose validity as the crack susceptibility index was verified recently. To deal with curved solidus and liquidus lines (i.e., variable equilibrium segregation coefficient k), fS was calculated as a function of T by numerical integration instead of by a simple analytical equation for constant k. Based on the secondary dendrite arm spacing λ2 in common Al arc welds and the λ2−tf data of Al alloys (tf is local solidification time), it was shown that back diffusion can occur in Al arc welding. Binary Al alloy systems were investigated over wide ranges of the eutectic temperature TE (229–548 °C) and k (about 0–0.87 at TE). It was shown that with a very low TE the crack susceptibility can still be relatively low if k is very high at TE to increase the effect of back diffusion on crack susceptibility reduction, consistent with the lower crack susceptibility of Al-Mg and even Al-Zn than Al-Cu. With both a very low TE and a very low k at TE, however, the crack susceptibility can be very high, consistent with the severe crack susceptibility of Al-Sn. The effect of the curvature of the liquidus and solidus lines on the crack susceptibility was shown. A possible link between the dihedral angle and bridging between grains was also shown.

Effect of grain boundary segregation on the deformation mechanisms and mechanical properties of nanocrystalline binary aluminum alloys

The deformation mechanisms of nanocrystalline (NC) pure Al and NC Al–Co and Al–Mg binary alloys are studied via molecular dynamics simulation. The alloying elements are either segregated to grain boundaries (GB) or distributed randomly as solute. It is revealed that a shear deformation of the pure Al is associated with the GB sliding (GBS) and simultaneous their migration (GBM). GB segregations can significantly alter the mechanisms of plastic deformation. Mg atoms in GBs of the Al–Mg alloy lead to GBS which is accompanied with GBM and a grain growth, while the deformation process of the corresponding alloy with the random distribution of Mg is close to that for pure Al. Unlike Mg, GB segregations of Co atoms detain both GBS and GBM and result in a higher strength of the Al–Co alloy. On the contrary, the strength of the alloy with the Co atoms distributed randomly is very low due to the structure amorphisation leading to the ease of plastic flow. The details of the GBS and GBM processes are further studied for tilt bi-crystals of Al and Al–Co and Al–Mg systems with the alloying atoms being either segregated to the GB or dissolved. It is found that the results for the bi-crystals are in line with those for the NC materials. Overall, GB segregation can strongly influence the response of NC alloys to thermomechanical treatment by affecting such very important mechanisms of plastic deformation in NC metallic materials as GBS and GBM.

Effect of Grain Boundary Segregation on Shear Deformation of Nanocrystalline Binary Aluminum Alloys at Room Temperature

The paper studies deformation mechanisms of nanocrystalline (NC) pure Al and its binary alloys with various distributions of an alloying element which can be Co or Mg via molecular dynamics simulations. It is revealed that a shear deformation of the pure Al is associated with the grain boundary sliding (GBS) and their simultaneous migration. Mg atoms in grain boundaries (GBs) of an Al-Mg alloy lead to GBS which does not accompany with a grain growth, while the deformation process of the corresponding alloy with a random distribution of Mg is close to that for the pure Al. Unlike Mg, GB segregations of Co atoms detain both GBS and GB migration and result in high strength of an Al-Co alloy. On the contrary, the strength of the alloy with the Co atoms distributed randomly is very low due to the structure amorphisation leading to the ease of plastic flow.

Thermal oxidation of the surface of binary aluminum alloys with rare-earth metals

The kinetics of oxidation of the surface of Al alloys with 1–2.5 at % rare-earth metals (REMs) at 400–500°C in air was studied by ellipsometry and X-ray photoelectron spectroscopy (XPS). The addition (1–2.5 at % REM) of all rare-earth metals to aluminum was shown to increase the thickness of the oxide layer. The addition of surfactant and chemically active REMs (Yb, Sm, La, and Ce) increased the rate of oxidation of solid aluminum most effectively. The oxidation can be accelerated by the polymorphic transformations of the individual REM oxides in the film. The surface activity of Sm with respect to solid Al was confirmed by XRS.

A Numerical Method for Microstructure Generation of a Binary Aluminum Alloy and Study of Its Mechanical Properties Using the Finite Element Method

A numerical method for the generation of the microstructure of a binary aluminum copper alloy is presented. This method is based on the repeated addition of some basic grain shapes into a representative volume element. Depending of the orientation of adjacent grains, different type of grain boundaries can be formed. The primary and secondary phases are distinguishable in our model and have distinct properties, reflecting the heterogeneous nature of the microstructure. The digital microstructure was then transformed into a finite element model. Using the finite element software ABAQUS, the stress distribution inside our heterogeneous material model has been studied and its mechanical properties have been found. That also makes possible to study and to visualize the cracks generated during the loading of the material where the local stress was sufficiently high. As a result of these analyses, the elastic modulus of such a heterogeneous domain and the effect of crack formation on ductility were evaluated.

Solution Strengthening of Various Elements in Aluminium Alloys

In the aluminium wrought alloys, the solid solution strengthening is one of the dominant hardening mechanism. Every solute element shows different strengthening effect. In present work the strengthening effect of different elements in a large temperature range was studied with the microstructure and flow stress model 3IVM+. This model was developed for cell forming metals, in which the work hardening and softening effects due to interaction of dislocation densities are taken into account. Compression tests for various binary aluminium alloys (Al-Mg, Al-Mn, Al-Si) were carried out under various deformation temperatures and strain rates. The contribution of each element to solution strengthening was investigated with 3IVM+. It was found that the dislocation interaction, especially cross slip and climb, is sensitive to the solute type and concentration.

Numerical Study of Variation of Mechanical Properties of a Binary Aluminum Alloy with Respect to Its Grain Shapes.

To study the variation of the mechanical behavior of binary aluminum copper alloys with respect to their microstructure, a numerical simulation of their granular structure was carried out. The microstructures are created by a repeated inclusion of some predefined basic grain shapes into a representative volume element until reaching a given volume percentage of the α-phase. Depending on the grain orientations, the coalescence of the grains can be performed. Different granular microstructures are created by using different basic grain shapes. Selecting a suitable set of basic grain shapes, the modeled microstructure exhibits a realistic aluminum alloy microstructure which can be adapted to a particular cooling condition. Our granular models are automatically converted to a finite element model. The effect of grain shapes and sizes on the variation of elastic modulus and plasticity of such a heterogeneous domain was investigated. Our results show that for a given α-phase fraction having different grain shapes and sizes, the elastic moduli and yield stresses are almost the same but the ultimate stress and elongation are more affected. Besides, we realized that the distribution of the θ phases inside the α phases is more important than the grain shape itself.

Formation of Zincate Films on Binary Aluminum Alloys and Adhesion of Electroless Nickel-Phosphorus Plated Films

Formation of Zincate Films on Binary Aluminum Alloys and Adhesion of Electroless Nickel-Phosphorus Plated Films

Decomposition Processes in the Anomalous Supersaturated Solid Solution of Binary and Ternary Aluminium Alloys Alloyed with Sc and Zr

Decomposition Processes in the Anomalous Supersaturated Solid Solution of Binary and Ternary Aluminium Alloys Alloyed with Sc and Zr

Fractal characteristics of dendrite in aluminum alloys

The fractal dimensions of dendrites in Al-Si and Al-Cu binary alloys were measured under furnace cooling and casting experiments. The fractal dimension of the Al-Si alloy increased from 1.275 to 1.495 along with increase in Si content. The fractal dimension of the Al-Cu alloy increased from 1.139 to 1.486 along with increase in Cu content. The fractal dimension of the binary alloys also increased with increase in cooling rate during solidification. Phase-field simulations for the evolution of the dendrites in the binary aluminium alloys were carried out and a same tendency as the experimental results was obtained. The permeability of an Al-5mass%Si alloy was estimated from the measured fractal dimension of an experimentally observed dendrite structure. The estimated permeability agreed well with reported permeability of an Al-Si alloy.

二元アルミニウム合金上の亜鉛置換皮膜形成と無電解Ni&amp;ndash;Pめっき皮膜の密着性

Formation of zincate films and adhesion of electroless nickel-phosphorus plated films were studied for binary aluminum alloys of Al–2at%Mn, Al–2at%Fe, Al–2at%Cu, Al–2at%Zn and high-purity aluminum (99.999 mass%). Precipitation mode of zinc in the zincate treatmens greatly varied according to the alloying elements in the substrates. In the cases of the first and the second zincate treatments for Al–Mn, Al–Fe and high-purity aluminum, zinc precipitated excessively, then, porous films of zinc repeatedly fell off the substrate. The surfaces of Al–Cu and Al–Zn alloys were immediately coated by uniform zincate films in the first and the second zincate treatments. Precip-itation of zinc is considered to be uniform if the oxide film on a substrate dissolves uniformly and rapidly in the zincate solution. When electroless nickel-phosphorus plating was conducted after the second zincate treatment of Al–Mn and Al–Fe alloys, the plated films easily peeled off. Those on Al–Cu and Al–Zn alloys showed excellent adhesion, and dimple patterns of the substrates were observed on the partly peeled areas. The poor adhesion is thought to be caused because the excess zinc dissolves at the beginning of the plating and generates hydrogen gas, then, gaps are formed between the plated films and the substrates.

Erbium and ytterbium solubilities and diffusivities in aluminum as determined by nanoscale characterization of precipitates

Binary aluminum alloys with 0.03–0.06 at.% RE (RE = Yb or Er) were aged to produce coherent, nanosize Al 3RE precipitates in an α-Al matrix. The temporal evolution of precipitate radii and matrix concentrations at 300 °C were measured by transmission electron microscopy and local-electrode atom-probe tomography, respectively. The temporal dependence of the matrix concentration of each RE was utilized to determine its solubility in Al. The solubility and the coarsening rate constants were used to determine the diffusivity of each RE in α-Al and the α-Al/Al 3RE interfacial free energies at 300 °C. When compared to Sc, both Yb and Er exhibited smaller solubilities but larger diffusivities in α-Al and larger α-Al/Al 3RE interfacial energies.

Evaluation of the Corrosion Resistance of Fe–Al–Cr Alloys in Simulated Low NO x Environments

Due to their excellent corrosion resistance, iron aluminum alloys are currently being considered for use as weld claddings in fossil fuel fired power plants. The susceptibility to hydrogen cracking of these alloys at higher aluminum concentrations has led researchers to examine the effect of chromium additions on the corrosion resistance of lower aluminum alloys. In this work, three iron aluminum alloys were exposed to simulated coal combustion environments at 500 and 700 °C for short (100 h) and long (5000 h) isothermal durations. Scanning electron microscopy was used to analyze the corrosion products. All alloys exhibited excellent corrosion resistance during short term exposures. For longer test times, increasing the aluminum concentration improved alloy corrosion resistance. The addition of chromium to the binary iron aluminum alloy prevented the formation iron sulfide and resulted in slower corrosion kinetics. A general classification of the scales developed on these alloys is presented.

Partial Grain Refinement in Al-3%Cu Alloy during ECAP at Elevated Temperatures

Microstructural changes during equal channel angular pressing (ECAP) in a temperature interval from 523 to 748 K (� 0:6{0:8 Tm) were studied in a coarse-grained binary aluminum alloy Al-3%Cu. Hot ECAP results in grain refinement taking place at all temperatures investigated, leading to a non-uniform development of deformation-induced fine grains and the remnant original grains containing subgrains with low-angle boundaries. Fine-grained structure is developed along microshear bands formed in grain interiors as well as along initial grain boundaries. The number and the average misorientation angle of the boundaries of microshear bands start to increase at above a critical strain of about 2, finally leading to development of new fine-grained structures. The volume fraction and the average misorientation of deformation-induced boundaries are reduced with rising temperature. The thermal stability of the evolved deformation microstructures and several factors controlling grain refinement during hot ECAP are discussed in details. [doi:10.2320/matertrans.MD200807]

Twinned dendrite growth in binary aluminum alloys

The formation of twinned dendrites (feathery grains) in binary Al–Zn, Al–Mg, Al–Cu and Al–Ni alloys has been studied in specimens directionally solidified under identical thermal conditions, i.e. G ≈ 100 K cm −1, v ≈ 1 mm s −1, and with slight natural convection in the melt. The influence of the solute element nature and content has been found to be of less importance than previously reported since feathery grains were formed in all four alloys, regardless whether the alloying elements are hexagonal close packed (Zn and Mg) or face-centered cubic with a high (Ni) or low (Cu) stacking fault energy. A detailed analysis confirmed that twinned dendrites grow along 〈1 1 0〉 directions in all four cases, with a complex branch morphology made of up to six to nine arms. Surprisingly, at high Zn or Mg compositions for which regular dendrites grow along 〈1 1 0〉 instead of 〈1 0 0〉, [Gonzales F, Rappaz M. Metall Trans A 2006; 37: 2797. [1]] no twinned dendrites could be formed. In terms of both the growth kinetics advantage of twinned dendrites over regular ones and the associated tip shape, some experimental evidence seems to contradict the doublon conjecture suggested by Henry [Henry S. PhD thesis, Ecole Polytechnique Fédéral de Lausanne, 1999. [21]], at least for the solute compositions studied in the present work.

Verification of a numerical model of macrosegregation in direct chill casting

PurposeThis paper aims to point out the critical problems in numerical verification of solidification simulation codes and the complexity of the verification and to propose and apply a procedure of generalized verification for macrosegregation simulation.Design/methodology/approachA partial verification of a finite‐volume computational model of macrosegregation in direct chill (DC) casting of binary aluminum alloys, including the coupled transport phenomena of heat transfer, fluid flow and species transport, is performed. The verification procedure is conducted on numerical test problems, defined as subproblems with respect to the complexity of the physical model, geometry, and boundary conditions. The studied cases are thermal convection with solidification in DC casting, thermal natural convection of a low‐Prandtl‐number liquid metal in a rectangular cavity and 1D directional solidification of a binary Al‐Cu alloy. Grid‐convergence studies, code comparison with an alternative Chebyshev‐collocation method, and comparison with a reference similarity solution are used for verification.FindingsAn excellent ability of the model to accurately resolve the thermal convection in the pertinent range of Prandtl and Rayleigh numbers is shown. Concerns regarding the solution of species transport in the mushy zone remain.Research limitations/implicationsThe proposed verification procedure is not completed in its entirety. Further verification of the solutal and thermosolutal convection problems is required.Originality/valueThis paper proposes verification techniques for complex coupled solidification problems involving significant convection in the melt.

Effect of Composition on the Photoelectrochemical Behavior of Anodic Oxides on Binary Aluminum Alloys

The photoelectrochemical behavior of anodic films on Al alloys, containing titanium, tantalum, and tungsten (valve metals), has been studied as a function of alloy composition and anodizing conditions. Photocurrent spectroscopy has been used to get information on bandgap and the flatband potential values of different mixed oxides. Both insulator-like and semiconducting behavior has been observed for anodic oxides grown on and alloys dependent on alloy initial composition. Optical bandgap values, , of different oxides are in accordance with predictions based on the correlation between and the difference of electronegativities of the oxide constituents, indicating potential for tailoring solid state properties of ternary oxides.