Cu-Al Solid Solutions Research Articles

The growth mechanisms of θ′ precipitate phase in an Al-Cu alloy during aging treatment

The plate-shaped θ′ (Al2Cu) precipitate acts as one of the primary strengthening phases in Al-Cu alloys. The interface, especially the semicoherent interface, between Al-Cu solid solution (αAl) and θ′ phase contains a lot of clues about phase transformations. Thus, these interfacial structures in an Al-Cu alloy after high-temperature and longtime aging have been analyzed in detail using atomic-scale high-angle annular dark-field scanning transmission electron microscopy and first-principles calculations in this work. It was found that the lateral growth of θ' precipitates is subjected to a combination of several major mechanisms under this aging condition. Except for some common intermediate phases, two novel and striking structures were observed on the interface, which implies two alternative atomic diffusion mechanisms for θ′ precipitate growth. For one condition, the atomic diffusion from αAl to θ′ phase transformation adopts an interstitialcy mechanism based on additional Al atoms. For the other condition, the diffusion is carried out through Al atoms. Both mechanisms are distinctly different from the previous theory based on direct diffusion of Cu atoms. The first-principle calculations also confirm that these newfound diffusion processes are energetically favored.

Microstructure of In-Situ Friction Stir Processed Al-Cu Transition Zone

The majority of literature sources dedicated to dissimilar Al-Cu friction stir welding testifies to the formation of intermetallic compounds (IMC) according to diffusion-controlled reactions, i.e., without liquation on the Al/Cu interfaces. Fewer sources report on revealing Al-Cu eutectics, i.e., that IMCs are formed with the presence of the liquid phase. This work is an attempt to fill the gap in the results and find out the reasons behind such a difference. Structural-phase characteristics of an in-situ friction stir processed (FSP) Al-Cu zone were studied. The single-pass FSPed stir zone (SZ) was characterized by the presence of IMCs such as Al2Cu, Al2Cu3, AlCu3, Al2MgCu, whose distribution in the SZ was extremely inhomogeneous. The advancing side SZ contained large IMC particles as well as Al(Mg,Cu) solid solution (SS) dendrites and Al-Al2Cu eutectics. The retreating side SZ was composed of Al-Cu solid solution layered structures and smaller IMCs. Such a difference may be explained by different levels of heat input with respect to the SZ sides as well as by using lap FSP instead of the butt one.

Investigating the grain structure of Cu-Al and Cu-Mn alloys via electron backscatter diffraction and optical metallography

Parameters of grain-boundary ensembles of Cu-Al and Cu-Mn solid solutions are analyzed quantitatively by optical metallography and scanning electron microscopy with the use of backscattering electron diffraction. It is established by both methods that the fraction of all special boundaries in a grain boundary ensemble and the fraction of twin boundaries Σ3 in the spectrum of special boundaries increase as the tacking fault energy in substitutional solid solutions diminishes.

Efficient Atomic-Scale Kinetics through a Complex Heterophase Interface

Atomic-scale imaging and first-principles modeling are applied to the heterophase interface between the Al-Cu solid solution (αCu) and θ' (Al2Cu) phases. Contrary to recent studies, our observations reveal a diffuse interface of complex but well-defined structure that enables the progression from αCu to θ' over a distance of ≈1 nm. We demonstrate that, surprisingly, the observed interfacial structure is not preferred on energetic grounds. Rather, the excess in interfacial energy is compensated by efficient atomic-scale kinetics of the αCu→θ' phase transformation.

Formation Process of {001} Texture in Al-Cu Solid Solution during High Temperature Compression Deformation

Uniaxial compression tests were conducted on Al-2.3mass%Cu and Al-4.6mass%Cu alloys under strain rates and temperatures ranging from 1.0×10-4s-1 to 5.0×10-2s-1 and 723K to 803K, respectively. Texture measurements reveal that main component of the fiber texture changes from {001} + {011} to {001} depending on the deformation conditions. EBSD measurements reveal that grain structure separates into large grains without subgrains and small and large grains with subgrains after the deformation at 803K under a strain rate of 5.0×10-2s-1 up to a strain of -1.0 in Al-4.6massCu alloy.

Small-angle scattering from GP zones in Al-Cu alloy

It is well known that Guinier Preston (GP) zones form in Al-Cu alloys upon solutionizing and artificial aging, which are extensively used in commercial practice. It is well established that GP zones are discshaped precipitates, i.e. disks of clusters of copper atoms in the FCC aluminium matrix. These disks have coherency strain fields in aluminium that give the alloy its high yield strength. The formation of GP zones in the supersaturated aluminium matrix is thought to be heterogeneous nucleation and growth. Some authors have believed that the formation of GP zones is by spinodal decomposition of the supersaturated Al-Cu solid solution. The main objective of the present work is to test whether spinodal decomposition is responsible for the formation of GP zones in Al-Cu alloy. The experimental alloy AA2219 was selected for its high copper content (Al-6%Cu-0·2%Zr). After solutionizing and artificial aging, the aging curve was plotted and small-angle scattering experiments were carried on the powdered samples as a function of time during artificial aging. Small-angle scattering data were analysed, and evidence has been obtained for the occurrence of spinodal decomposition as the mechanism responsible in the early stages of formation of GP zones.

Microstructure evolution of Zr2Al3C4 in Cu matrix

Abstract

Formation of AlCuFe icosahedral quasicrystal by mechanical alloying: XAFS and XRD studies

The structural evolutions of the mechanically alloyed ternary Al 70Cu 20Fe 10 powders with the milling times and the annealing treatment were studied by X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS). It was found that during the milling process, only Cu can incorporate into the lattice of Al to form an Al 2Cu compound or an AlCu solid solution, depending on the milling times. However, Fe remains the original structure of bcc α-Fe. Annealing treatment at 700 °C for 4 h can drive the α-Fe to react with the Al 2Cu compounds and AlCu solid solution, and the main products of the annealed Al 70Cu 20Fe 10 (10 h) and the annealed Al 70Cu 20Fe 10 (40 h) are the icosahedral Al 65Cu 20Fe 15 quasicrystal and the Al(Cu, Fe) solid solution, respectively. The local structural disorders around Fe and Cu atoms in the icosahedral QC phase is about 50% larger than those of the Al(Cu, Fe) solid solution.

About stress reduction experiments during constant strain-rate deformation tests

Abstract Stress reduction experiments have been performed during constant strain-rate compression tests of single crystals of Ge, Cu, CuAl solid solutions and Ni3Al. These tests allow one to separate the components of the applied stress. They provide useful information about the spatial oscillation of the internal stress, the influence of temperature and strain-rate on the internal and the effective stresses. Activation volume values can be obtained and the Cottrell – Stokes behavior can be checked. Different features of the thermally activated deformation mechanisms in the studied crystals are discussed.

Effect of Powder Characteristic on Al Internal Oxidation to Prepare Al2O3- Cu Composite

Effects of powder characteristics on the internal oxidation of Cu-Al prealloyed powders were discussed. The results show that the internal oxidation of Al was occurred during sintering not in ball milling when the content of Al in Cu-Al prealloyed powders was 0.8wt.%, the mechanism of Al internal oxidation was different with the milling time, when the milling time was short, the internal oxidation of Al during sintering were mainly the unsolved Al and absolute Cu-Al solid solution resulted in coarse Al2O3 and fine Al2O3 particles respectively. When the mixed powders were milling for time long enough, the internal oxidation of Al during sintering was all the metastable Cu-Al prealloyed. A good quality Al2O3-Cu composite was prepared. The Al2O3 particles with an average size 2-5 mm in diameter and about 5-10 mm in particle spacing have been observed uniformly dispersed in the composite prepared by prealloyed powders after milling 96 h.

Self-Regulation of the Cathodic Reaction Kinetics during Corrosion of AlCu Alloys

AlCu solid-solution alloys were dealloyed by immersion in alkaline solution to produce a high surface density of copper nanoparticles, simulating the region around a cathodic intermetallic phase in an industrial AlCuMg alloy. The cathodic behavior of the copper-enriched surface in neutral chloride or sulfate solutions showed an abnormally low limiting current density for oxygen reduction, less than 10% of the value shown by a planar copper electrode, but if the solution was substituted by a borate buffer, the limiting current increased sharply. In the unbuffered solution there is corrosion of the aluminum by cathodically generated alkali, and the surface pH rises to the value where the net or apparent cathodic limiting current density maintains the surface pH at about 9 [for a polarization potential around −800 mV (SCE)]. This process greatly reduces the available cathodic current to drive remote pits or crevice corrosion sites. The implications for corrosion in real environments of varying buffer capacity are discussed. © 2002 The Electrochemical Society. All rights reserved.

The influence of stacking fault energy on the mechanical behavior of Cu and Cu-Al alloys: Deformation twinning, work hardening, and dynamic recovery

The role of stacking fault energy (SFE) in deformation twinning and work hardening was systematically studied in Cu (SFE ∼78 ergs/cm2) and a series of Cu-Al solid-solution alloys (0.2, 2, 4, and 6 wt pct Al with SFE ∼75, 25, 13, and 6 ergs/cm2, respectively). The materials were deformed under quasi-static compression and at strain rates of ∼1000/s in a Split-Hopkinson pressure bar (SHPB). The quasi-static flow curves of annealed 0.2 and 2 wt pct Al alloys were found to be representative of solid-solution strengthening and well described by the Hall-Petch relation. The quasi-static flow curves of annealed 4 and 6 wt pct Al alloys showed additional strengthening at strains greater than 0.10. This additional strengthening was attributed to deformation twins and the presence of twins was confirmed by optical microscopy. The strengthening contribution of deformation twins was incorporated in a modified Hall-Petch equation (using intertwin spacing as the “effective” grain size), and the calculated strength was in agreement with the observed quasi-static flow stresses. While the work-hardening rate of the low SFE Cu-Al alloys was found to be independent of the strain rate, the work-hardening rate of Cu and the high SFE Cu-Al alloys (low Al content) increased with increasing strain rate. The different trends in the dependence of work-hardening rate on strain rate was attributed to the difference in the ease of cross-slip (and, hence, the ease of dynamic recovery) in Cu and Cu-Al alloys.

Mean-square displacement and compression effect on melting point of Al-Cu solid solution

Mean-square displacement and compression effect on melting point of Al-Cu solid solution

Steady State Creep in Cu-Al Solid Solution Alloys at Intermediate Temperatures and Low Stresses

Article Steady State Creep in Cu-Al Solid Solution Alloys at Intermediate Temperatures and Low Stresses was published on January 1, 1993 in the journal High Temperature Materials and Processes (volume 12, issue 1-2).

Elastic Constants of Al-Cu Solid-Solution Alloys and Their Variations by Aging Treatments

Elastic Constants of Al-Cu Solid-Solution Alloys and Their Variations by Aging Treatments

Creep and ductility in an Al-Cu solid-solution alloy

High-temperature creep was investigated in an Al-3 wt pct Cu alloy at temperatures in the range of 773 to 853 K and at a normalized shear stress range extending from 10-5 to 7 × 10-4. The results show the presence of three distinct regions. In region I (low stresses), the stress exponent is 4.5 and the activation energy is 155 kJ/mole. In region II (intermediate stresses), the stress exponent is 3.2 and the activation energy is 151 kJ/mole. In region III (high stresses), the stress exponent is 4.5 and the activation energy is 205 kJ/mole. Creep curves obtained in the three regions exhibit a normal primary stage, but the extent of the stage is less pronounced in region II than in regions I and III. The creep characteristics in regions I and II, along with the values of the transition stresses between the two regions, are in conformity with the prediction of the deformation criterion for solid-solution alloys. While the advent of region III (high stresses) correlates well with dislocation breakaway from a solute-atom atmosphere, the creep characteristics in this region are not entirely consistent with any of the existing high-stress creep mechanisms. The plot of elongation to fracturevs initial strain rate at 853 K exhibits two peaks at strain rates of 1 × 10-4 and 6 × 10-4 s-1. The first peak (1 × 10-4 s-1) is attributed to the variation of the stress exponent for creep in the alloy with strain rate, and the second peak (6 × 10-4 s-1) appears to reflect the effect of solute drag on dislocation velocity.

Elastic constants of Al-Cu solid-solution alloys and its variations by aging treatments.

Supersaturated solid-solutioning alloys of the Al-Cu system of up to 8at%Cu were prepared by means of heat treatments under the pressure of 5.4 GPa and the temperature of 720 °C for 10 hours. The elastic constants of the specimens obtained were measured by a three dimensional resonance method. The Young's modulus E and shear modulus G of the solid solutions were increased with Cu contents, and such features related to the number of electrons per atom ratio were discussed by free electron theory. The specimens of solid solutions were then isochronally aged up to 450 °C, and the variations of the elastic constants were measured step by step. The maximum shear modulus was observed during the precipitation of the θ' phase at 300°C-aging. Temperature coefficients of the moduli were also measured on the several specimens of different treatments.

Surface and Subsurface Behavior of Selected Al-Cu Alloys in Sliding Wear

As materials are pushed to higher levels of performance, the nature of friction and wear phenomena occurring in sliding contact is of even greater importance in view of energy efficiency and maintained functional integrity. The present study investigated unlubricated sliding wear from the standpoint of transfer layer behavior. Microscopic studies of selected Al-4.5 Cu structures confirmed that asperity contact damage is very localized, as was the case for previously studied solid solutions. The subsurface region was found to consist of very fine crystallites lacking a stable, definable texture. Macroscopic wear testing was performed by three different methods using Cu-Al solid solutions. It was demonstrated that test multiplicity has the advantages of establishing machine-dependent results and also showing conditions for which a given parameter is rate controlling. Surface-sensitive tests using aluminum bronzes are dominated by surface oxide effects. The soft Cu2O component of films on low percentage solute alloys behaves as a solid lubricant. When tests are employed that produce more severe wear, bulk properties of the substrate predominate except for alloys with highly abrasive surface oxides. Results of this study have been found to be in good correlation with related transfer layer investigations.

Etude par microscopie electronique d'un alliage aluminium-cuivre a 1.3% atomique obtenu par implantation

An Al-Cu alloy of 1.3 at% is obtained by implantation of Cu ions in thin foils of aluminium. The purpose of the electron-microscope study is to determine the ageing reactions of this alloy as compared with those occuring in the quenched solid solution. It has been shown that the implantation temperature is an essential parameter in the unmixing process. After a 77 K implantation 8 months of ageing at 20°C are necessary to obtain the first stages of unmixing characterized by the formation of Guinier-Prestion I zones (GP(I) zones), whereas after an implantation at room-temperature, the θ″ phase is directly observed. The behaviour of the solid solution obtained at 77 K is similar to the conventional Al-Cu solid solution. On the contrary, during the implantation at room-temperature, the unmixing is already started and this fact can be explained on account of an enhanced diffusion.

On some X-ray diffuse scattering effects on Cu–Al single crystals

A change in the diffuse scattering intensity distribution as a function of Al concentration in the α-phase Cu-Al solid solution is examined. The shape and intensity of the diffuse{\bar 1}11 and 020 reflexions are shown to change with increasing Al concentration. With 10 at.% AI as the starting point, new diffuse reflexions appear. These are interpreted in terms of the formation of new Al atom configurations.