Intermetallic Al2Cu Research Articles

Rapid fabrication and corrosion behavior of 3D-porous Cu-Al-Si compounds via low-energy self-exothermic reaction

In this study, porous Cu-Al-Si intermetallic compounds with three-dimensional structures were rapidly prepared by a novel self-exothermic reaction. By this method, Si was successfully solid-solved into CuAl intermetallic compounds and achieved better fusion with them. The effects of Si addition on their oxidation resistance and corrosion resistance were compared. The findings indicate that the minimum weight gain of the Cu-Al-Si product is only 1.48% after oxidation at 800 °C for 288h. Si facilitates the creation of a continuous Al2O3 protective layer on the surface of the porous Cu-Al-Si intermetallics skeleton, thereby preserving its internal structure while significantly enhancing its oxidation resistance. The incorporation of Si to Cu-Al intermetallics enhances the stability of the passivation film on the material's surface, increases the resistance of the passivation film, and effectively restricts the electrochemical reaction between the material and the corrosive medium.

Microstructure and localized corrosion properties of 2219 aluminum alloy manufactured by additive friction stir deposition

Multi-layer 2219 aluminum alloy samples were successfully fabricated using additive friction stir deposition (AFSD). AFSD deposition reduced grain size and the size of intermetallic Al2Cu particles, but greatly increased the amount of Al2Cu particles. More Al2Cu particles increased the number of galvanic microcells on alloy surface and at the grain boundaries, which promoted the localized corrosion and improved the intergranular corrosion sensitivity of AFSD alloy. Subsequent T6 heat treatment had little effect on grain size but enhanced the corrosion resistance of AFSD alloy, primarily attributed to the reduction in Al2Cu particles and the elimination of dislocations within grains.

Thermal Misfit and Diffusion Induced Stresses of Cu-Al Intermetallics in Microelectronics Wire Bonding

The thermosonic bonding technique is a widely used method for Cu wire interconnections. However, issues arise due to volumetric changes in intermetallic compounds (IMCs) formed at the Cu-Al bonding interface, leading to voids in the Cu-Al IMC layer. This problem is exacerbated after annealing, such as in high-temperature Storage (HTS). In this study, a statistical modelling approach was employed to quantitatively analyse stress, studying the evolution and characteristics of the interfacial microstructure in the thermosonic Cu wire-Al bond pad system. Microstructural analysis focused on Cu-Al IMC crystallography and compositional classification. A stress model was proposed, considering both thermal misfit and diffusion-induced stresses. Results showed that interfacial stress generally increased with higher bonding temperatures. The influence of forming gas supply was relatively minor, with oxide layers minimally impeding Cu-Al interdiffusion during Cu-Al IMC formation. This stress modelling technique hold potential as a valuable failure analysis tool for implementing Cu wire in various industries.

Purification of the Al2Cu intermetallic compound via zone melting crystallization technique

The widespread interest in intermetallic compounds has driven the development of their structures and properties, as well as their applications as alternative structural and potentially functional materials. As more and more intermetallic compounds with complex compositions enter the application market, their performance improvement and sustainable recycling face many challenges, where the influence of impurities plays a crucial role. Here, we proposed the direct purification of intermetallic compounds by fractional crystallization and verified for the first time the feasibility and effectiveness of zone melting for the purification of intermetallic Al2Cu. After ten passes of zone melting, results showed no separation of Al and Cu, the major components of Al2Cu. Further analyses demonstrated the homogeneity and remelting stability of Al2Cu before and after zone melting. In addition, the total impurity concentrations at the front and the end of cast Al2Cu bars decreased with increasing number of passes, respectively. After ten passes of zone melting, Al2Cu bar with an initial purity of 3N exhibited higher refining efficiency than those with an initial purity of 4N. Among all impurities, the distribution coefficients of Fe, Si, Zn, and Ti were obviously less than unity (k < 1). Whereas the impurities Ca, Mg and Mn showed behaviors of distribution coefficients less than and/or close to unity.

Insight on corrosion behavior and mechanism of AA2219 friction stir welded joint in N2O4 medium

This paper investigated the corrosion behavior of AA2219 friction stir welded joints in N2O4. The results showed that with the extension of immersion time, corrosion behaviors such as pitting, intergranular corrosion, and exfoliation corrosion occurred in both base material and weld nugget zone, but there are differences in corrosion sensitivity, and the corrosion behavior mechanism and corrosion sensitivity differences were further analyzed. Pitting was caused by the dissolution of the aluminum matrix near the intermetallic Al2Cu. In addition to the potential differences, intergranular corrosion was also related to grain boundary misorientation and differences in grain boundary precipitates. Corrosion products observed visually at the intergranular corrosion position were helpful in understanding the corrosion mechanism. This work is the first to systematically investigate and report the evolution in corrosion behavior and mechanism of AA2219 FSW in N2O4, which can be a reference for the study of aerospace aluminum alloy materials.

Formation of Cu-Al layered materials by detonation spraying and modification of the interface by annealing/spark plasma sintering

Cu-Al layered structures are frequently encountered in electrical and electronic devices and facilities as both metals possess a high electrical conductivity. In the present work, a new approach was used to fabricate Cu-Al bi-layers. The layers were formed by successively depositing copper and aluminum on a steel substrate by detonation spraying. The layered structures were annealed in a vacuum furnace or treated by electric current in a spark plasma sintering (SPS) facility. Both furnace annealing and SPS induced the formation of Cu-Al intermetallics, the thickness of the product layers being greater after the SPS treatment. The effect of applied pressure alone could not fully account for the difference between the outcomes of furnace annealing and SPS. The main products formed during both annealing and SPS were CuAl2 and Cu9Al4. The application of pressure during SPS allowed eliminating the interfacial porosity. Conventional annealing was not instrumental for this purpose.

On the Evolution of Nano-Structures at the Al-Cu Interface and the Influence of Annealing Temperature on the Interfacial Strength.

Molecular dynamics (MD) simulations are invoked to simulate the diffusion process and microstructural evolution at the solid–liquid, cast-rolled Al–Cu interfaces. K-Means clustering algorithm is used to identify the formation and composition of two types of nanostructural features in the Al-rich and Cu-rich regions of the interface (i.e., the intermetallic Al2Cu near the Al-rich interface and the intermetallic Al4Cu9 near the Cu-rich interface). MD simulations are also used to assess the effects of annealing temperature on the evolution of the compositionally graded microstructural features at the Al–Cu interfaces and to characterize the mechanical strength of the Al–Cu interfaces. It is found that the failure of the Al–Cu interface takes place at the Al-rich side of the interface (Al2Cu–Al) which is mechanically weaker than the Cu-rich side of the interface (Cu–Al4Cu9), which is also verified by the nanoindentation studies of the interfaces. Centrosymmetry parameter analyses and dislocation analyses are used to understand the microstructural features that influence deformation behavior leading to the failure of the Al–Cu interfaces. Increasing the annealing temperature reduces the stacking fault density at the Al–Cu interface, suppresses the generation of nanovoids which are precursors for the initiation of fracture at the Al-rich interface, and increases the strength of the interface.

Diffusion Bonding of Al7075 to Ti-6Al-4V by Spark Plasma Sintering and Using a Copper Interlayer

Sheets of aluminum 7075 and titanium Ti-6Al-4V alloys were successfully joined using the spark plasma sintering (SPS) process. A copper foil was placed as an interlayer between the two surfaces. The bonding was made at 480 °C, 500 °C, and 520 °C with a holding time of 10 min and under a uniaxial pressure of 5 MPa and 10 MPa. The obtained bonds were analyzed by scanning electron microscopy, energy dispersive spectroscopy (SEM/EDS), and wavelength dispersive spectroscopy (WDS). It was found that copper diffused away through Al7075 and formed Al2Cu intermetallics but was not present at the joint region. The investigation of the fractured surfaces using X-ray diffraction (XRD) showed that the joint region contained TiAl3, TiAl2, and Ti3Al intermetallic compounds. The presence of the Cu foil was believed to hinder the formation of Al3Ti observed in previous studies by allowing more Ti to diffuse into the Al side.

Ultrafine-Grained Microstructures of Al-Cu Alloys with Hypoeutectic and Hypereutectic Composition Produced by Extrusion Combined with Reversible Torsion.

In this study, binary as-cast Al–Cu alloys: Al25Cu (Al–25%Cu) and Al45Cu (Al–45%Cu) (in wt%) were severely plastically deformed by extrusion combined with a reversible torsion (KoBo) method to produce an ultrafine-grained structure (UFG). The binary Al–Cu alloys consist of α-Al and intermetallic Al2Cu phases. The morphology and volume fraction of α-Al and Al2Cu phases depend on the Cu content. The KoBo process was carried out using extrusion ratios of λ = 30 and λ = 98. The effect of phase refinement has been studied by means of scanning electron microscopy with electron backscattering diffraction and scanning transmission electron microscopy. The mechanical properties were assessed using compression tests. Detailed microstructural analysis shows that after the KoBo process, a large number fraction of high-angle boundaries (HABs) and a very fine grain structure (~2–4 μm) in both phases are created. An increase of λ ratio during the KoBo processing leads to a decrease in average grain size of α-Al and Al2Cu phases and an increase in fraction of HABs. UFG microstructure and high fraction of HABs provide the grain boundary sliding mechanism during KoBo deformation. UFG microstructure contributes to the enhanced mechanical properties. Compressive strength (Rc) of Al25Cu alloy increases from 172 to 340 MPa with an increase of λ. Compressive strain (Sc) for Al25Cu alloy increased from 35 to 67% with an increase of λ. High fraction of intermetallic phase in Al45Cu alloy was responsible for room temperature strengthening of alloy and low compressive strain. The deformed Al45Cu alloy with λ = 30 showed that Rc is 194 MPa and Sc is equal to 10%.

Aluminum-copper alloy anode materials for high-energy aqueous aluminum batteries

Aqueous aluminum batteries are promising post-lithium battery technologies for large-scale energy storage applications because of the raw materials abundance, low costs, safety and high theoretical capacity. However, their development is hindered by the unsatisfactory electrochemical behaviour of the Al metal electrode due to the presence of an oxide layer and hydrogen side reaction. To circumvent these issues, we report aluminum-copper alloy lamellar heterostructures as anode active materials. These alloys improve the Al-ion electrochemical reversibility (e.g., achieving dendrite-free Al deposition during stripping/plating cycles) by using periodic galvanic couplings of alternating anodic α-aluminum and cathodic intermetallic Al2Cu nanometric lamellas. In symmetric cell configuration with a low oxygen concentration (i.e., 0.13 mg L−1) aqueous electrolyte solution, the lamella-nanostructured eutectic Al82Cu18 alloy electrode allows Al stripping/plating for 2000 h with an overpotential lower than ±53 mV. When the Al82Cu18 anode is tested in combination with an AlxMnO2 cathode material, the aqueous full cell delivers specific energy of ~670 Wh kg−1 at 100 mA g−1 and an initial discharge capacity of ~400 mAh g−1 at 500 mA g−1 with a capacity retention of 83% after 400 cycles.

Effect of Cu on microarc oxidation coated Al–xCu alloys

ABSTRACT Microarc oxidation (MAO) coatings were produced on the Al–Cu alloys at different oxidation times. Surface morphologies, phase composition and residual stress, and wear resistance were analysed by SEM and a laser scanning confocal microscopy, X-ray diffraction, and reciprocating friction and wear tester, respectively. Increases in surface roughness, porosity, cracks, thickness, and α-Al2O3 content were found in the MAO coatings on Al–4.5Cu alloy. Presence of intermetallic Al2Cu in the Al–4.5Cu alloy improved wear resistance and induced residual compressive stress formation in the coatings. Heat accumulation of intermetallic Al2Cu was the key factor that led to the differences in coating microstructure and nature of residual stress. In addition, mechanical properties of the coated samples were slightly changed compared to that of bare Al–Cu alloys. Presence of intermetallic Al2Cu was advantageous to wear resistance and oxide film formation of MAO coated Al–Cu alloys.

Mechanism of corrosion inhibition of intermetallic Al2Cu in acidic solution

The objective of this work was to study the kinetics of phosphomolybdenum blue formation onto the surface of intermetallic Al2Cu in orthophosphoric acid solution. This was performed using UV–Vis spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and electrochemical methods. The latter included measurement of open circuit potential, cyclic voltammograms, polarisation, and chronoamperometric curves as well as impedance spectra. It was shown that a stable form of phosphomolybdenum blue is formed via decomposition of an intermediate in the solution. However, neither phosphomolybdenum blue nor heteropolyoxomolybdate species behave as a corrosion inhibitor. A protective layer of molybdenum oxides formed immediately upon immersion of intermetallic in the corrosive environment, is responsible for corrosion inhibition.

Dislocation-mediated plasticity in the Al2Cu θ-phase

The deformation behaviour of the intermetallic Al2Cu θ-phase was investigated using atomistic simulations and micropillar compression, where slip on the unexpected {211} and {022} slip planes was revealed. Additionally, all possible slip systems for the intermetallic phases were further evaluated and a preference for the activation of slip systems based on their effective interplanar distances as well as the effective Burgers vector is proposed. The effective interplanar distance corresponds to the manually determined interplanar distance, whereas the effective Burgers vector takes a potential dislocation dissociation into account. This new order is: {211}½<111>, {022}½<111> and {022}<100>, {110}<001>, {310}<001>, {022}<011>, {110}½<111>, {112}<110> and {112}½<111> from high to low ratio of deff/beff. Also, data on the critical resolved shear stresses of several of these slip systems were measured.

Modeling of material flow in dissimilar friction stir lap welding of aluminum and brass using coupled Eulerian and Lagrangian method

Dissimilar friction stir welding of metals is crucial in terms of inter-material mixing and the intermetallic compound formation which affects the achieving a sound joint with fine mechanical properties. In this investigation, the formation of intermetallic compounds along with the material flow during friction stir lap welding (FSLW) of aluminum and brass is studied. First, the experimental investigations were performed using SEM, EDS, and XRD to probe the chemical compositions and intermetallic formation in the stir zone (SZ). Experimental results show the presence of Al2Cu and Al4Cu9 intermetallics in the SZ while are dispersed in separated zones. Moreover, to study further the material mixing, the coupled Eulerian-Lagrangian (CEL) method is employed to simulate the SZ formation during the FSLW of aluminum and brass. The model successfully predicts the SZ formation and material mixing in the Al/CuZn34 interface with penetration of Al into brass at the center and penetration of earring shape brass into Al sheet at the periphery of the SZ. Results show that two distinct zones inside the SZ could be observed, in which one is filled mostly by Al2Cu intermetallics near the Al sheet and the other is filled mostly by Al4Cu9 near the brass sheet. Additionally, by increasing the tool traverse speed, the amount of inter-material mixing significantly decreases, but on the other hand, the formation of intermetallic phases, which reduces the mechanical properties of the joint, is restricted.

Corrosion of structural constituents of 2017 aluminium alloy in acidic solutions containing inhibitors

AbstractThe objective of this study is to establish the corrosion behaviour of the most important structural constituents of the aluminium alloy 2017 in orthophosphoric acid solutions containing heteropolyoxomolybdate, tungstate and vanadate. These are potential candidates for replacing toxic hexavalent chromium species in stripping solution for anodic coatings. The corrosion rate of the alloy is estimated with linear polarisation method. It decreases from 0.58 mA cm−2 in uninhibited solution to 0.10 mA cm−2 in a solution containing heteropolyoxomolybdate species. Microscopic studies reveal that heteropolyoxomolybdate species inhibit corrosion of the matrix and intermetallic Al15(Fe,Mn)3(Si,Cu)2 but not Mg2Si. Intermetallic Al2Cu remains not corroded. Heteropolyoxotungstate species virtually do not inhibit the corrosion of the alloy. The solution containing vanadium species is not stable with time and the corrosion rate is not determined. Nevertheless, corrosion of the matrix is inhibited, but intermetallics Al15(Fe,Mn)3(Si,Cu)2 together with Mg2Si are dissolved. X‐ray photoelectron spectroscopy is used for examination of a corrosion product precipitated on the surface.

Influence of secondary phases of AlSi9Cu3 alloy on the plasma electrolytic oxidation coating formation process

To understand the formation and growth of plasma electrolytic oxidation (PEO) coatings in presence of different secondary phases in a substrate, PEO treatment was carried out on AlSi9Cu3 alloy at different treatment times ranging from 15 s to 480 s. The coating formation and evolution process was traced by surface and cross-sectional observation of the layers on the different phases of the alloy. The results demonstrated a sequential involvement of the different phases in the plasma discharges: firstly, discharges start on the α-Al matrix, then on the intermetallic Al2Cu and β-Al5FeSi phases at the same time and finally on the eutectic Si. The presence of intermetallic Al2Cu remarkably affects the initial dissolution, the deposition of conversion products and the ignition of discharges at the early stages of processing. Eutectic Si in the substrate exhibits the highest electrochemical stability at all stages and contributes in the beginning to a distinct coating morphology eventually. The resultant PEO coating tends to be uniform if processing times are longer and a double-layer structure appears in the coating.

Cu-Al interfacial formation and kinetic growth behavior during HTS reliability test

Reverse engineering techniques of Cu wire bonding process used in manufacturing microelectronic packing components are proposed for evaluating Cu-Al intermetallic phases. The High Thermal Storage (HTS) in the molded bond reliability test and Cu-Al IMC coverage estimation method on Cu ball-bonded parts contribute to increased production efficiency and improved bonding process quality. The results show that distinct intermetallics of microscopic lamellar structures were identified as CuAl2, CuAl and Cu9Al4 after thermal annealing to 2000 h at 150 °C. After post annealing process, voids appear here are too small to pose a threat to reliability concern and Al fragments emerge during bonding process accompanied with smaller diffusion voids are highly connected to create more robust intermetallics. The growth kinetics of Cu-Al intermetallic compound was determined simultaneously during annealing tests. From Arrhenius equation, the growth rate of intermetallic formation (k) has been obtained under three different annealing temperatures and calculated its activation energy of 76.13 kJ/mol and the growth rate constant of k0 = 46.47 μm2/s. The obtained universal equation of layer thickness can be acted as the prediction model for the guideline of intermetallic growth behavior under thermal effect which diminished the Cu-Al interface failures for practical field application. Cu-Al intermetallics coverage inspection and ball shear test was investigated in the unmolded bake reliability test, which addressed the specification of IMC coverage >80% and typical minimum shear strength of 6.67 g/mil2 ( = 10.34 Kg/mm2).

An approach for fabrication of Al-Cu composite by high pressure torsion

The method utilizing high-pressure torsion (HPT) processing followed by annealing to fabricate Cu-Al in situ composite with enhanced mechanical properties is presented. The initial sample consists of three metal discs Cu/Al/Cu was processed by HPT (5 GPa, 5 turns). The analyses of the microstructure after HPT carried out by transmission electron microscopy and scanning electron microscopy equipped with energy dispersive spectrometry (EDS). After HPT, the development of nanostructure with the mean crystallite size of about 100 nm in the produced sample was revealed with the small presence of the intermetallic phases. Investigation of the kinetics during subsequent annealing at 450 °C/30 min showed the in situ formation of intermetallic Al2Cu, AlCu, Al3Cu4, Al2Cu3 and Al4Cu9 phases in the copper matrix which was detected by EDS. The formation of intermetallic phases after annealing was also confirmed by X-ray diffraction. The results showed that microhardness of the composite considerably increases from an initial value of ∼380 for HPT sample to a saturation value of ∼900 after annealing.

Preparation and Growth Characterization of Al2Cu Phase Crystal with the Single Orientation Under Directional Solidification

Through decreasing the sample size, the regular faceted rectangular Al2Cu phase crystal was prepared under directional solidification. Effects of sample size on the microstructure morphologies and orientations of intermetallic Al2Cu phase crystal growth at 10 µm/s have been characterized and investigated. The transverse-section microstructure of primary Al2Cu phase crystal transited from L-shaped pattern to regular faceted rectangular pattern with a single preferred orientation at [001] direction with sample size decreasing. By using the serial sectioning technique, the three-dimensional (3D) microstructure of Al2Cu phase in 0.45 mm sample was observed as rectangular parallelepiped. Moreover, the faceted interfaces of Al2Cu phase crystal were determined as {110} planes. Based on growth characteristics of the Al2Cu phase crystal, a growth mode in different sizes samples under directional solidification was proposed. The experimental results show that a regular microstructure with preferred single orientation can be achieved in small-size sample during directional solidification.

Fabrication of Highly Porous CuAl Intermetallic by Thermal Explosion Using NaCl Space Holder

A high-porosity CuAl-based intermetallic compound with composition Cu-50 at.% Al has been successfully prepared by thermal explosion (TE) using NaCl as space holder. The results showed that the NaCl particles were completely removed from the green compact by water leaching. The temperature of the specimen during the TE and the evolution of the porous microstructure were investigated. The TE was ignited at 560°C, and the specimen temperature increased to 775°C in 3 s, resulting in formation of intermetallic CuAl and CuAl2 phases in the final product. A porous CuAl-based intermetallic compound with up to 62 vol.% open porosity was produced when adding 60 vol.% NaCl. The compound exhibited a bimodal pore size structure, including large pores (200 μm to 300 μm) that replicated the NaCl particles and small pores (5 μm to 10 μm) interspersed in the pore walls. Moreover, the large pores were interconnected by channels and formed an open CuAl-based intermetallic cellular structure, having great potential for use in heat exchange and filtration applications.