Al-Cu Alloys Research Articles

Enhanced strength-plasticity of 2319 Al-Cu alloy formed by hybrid interlayer friction stir processing and wire-arc additive manufacturing

Enhanced strength-plasticity of 2319 Al-Cu alloy formed by hybrid interlayer friction stir processing and wire-arc additive manufacturing

Corrosion behavior assessment of an Al-Cu alloy manufactured via laser powder bed fusion

Additively manufactured Aluminum-Copper alloys are attracting interest because of their high tensile strength. Nevertheless, the presence of Cu strongly affects the corrosion performances. In this work, the corrosion behavior of an innovative laser powder bed fusion-processed 2139 alloy was investigated, and its corrosion performances were compared to the well-consolidated AlSi10Mg alloy, as well as the parent wrought alloy. Electrochemical, Kelvin probe microscopy and intergranular corrosion tests were performed. The unique corrosion morphology at melt pool boundaries are presented and discussed alongside with the effect of surface finishing and heat treatments.

Contribution of the Fe-rich phase particles to the high temperature mechanical behaviour of an Al-Cu-Fe alloy

The high temperature strengthening mechanisms in Al-Cu-Fe aluminium alloy was analysed basis on a comprehensive microstructural study of the as-cast alloy and mechanical testing results. An approach which extracts the specific contribution of solid solution atoms, precipitates, and Fe-rich particles to the creep strengthening was utilized. Additionally, the Shear Lag model, was employed to account for the contribution to strengthening of the Fe-rich intermetallic particles through a load transfer mechanism. For this study, an as-cast Al-Cu alloy, which does not contain Fe impurities, has been also used for comparative purposes. The findings suggest that the large and 3D interconnected Fe-rich phase particles (Al6(MnFe) and α-Fe) generate the main strengthening effect at high temperature through a load transfer mechanism, whereas the contribution of the nanometric Al2CuMg precipitates were very limited.

Integrated control mechanism of ultrasound and ZrO2 particles on differential microstructures for the wire arc additive manufacturing

ABSTRACT Inhibiting unhomogenised microstructure during the directed energy deposition process with the electric arc energy source (DED-Arc) has become a significant challenge. Ultrasonic vibration leads to the severe stirring of liquid metal and break down dendrites in the inner-layer zone, which promotes the formation of fine grains after rapid solidification. In contrast, the grain refinement effect is not obvious in the semi-melting zone. The addition of ZrO2 particles in the 2319 Al-Cu alloy during the DED-Arc process can drag and pin the grain boundary to prevent grain coarsening in the semi-melting zone. Under the integrated effect of ultrasound and particles, ZrO2 particles can be evenly distributed in different regions, which is beneficial to enhance the microstructure uniformity of the deposition layer and ultimately achieving significant improvement in mechanical properties. The intergrated effect of ultrasonic vibration and particles on strength and elongation reach 13.8% and 92.4%, respectively.

Transmission electron microscopy of the rapid solidification microstructure evolution and solidification interface velocity determination in hypereutectic Al-20at.%Cu after laser melting

The evolution of rapid solidification (RS) microstructure and solidification interface velocity has been studied experimentally by in-situ transmission electron microscopy and postmortem characterization for hypereutectic Al-20at.%Cu (37 wt.%Cu) after laser melting. Four morphologically distinct regions formed via growth modes changing from θ-Al2Cu phase dendrites to eutectic cell growth, possibly α-Al dendrite growth (α-cell), banded growth, and α-Al plane front growth. Tendency for faceting and low capacity for solute trapping limited the θ-phase dendrite growth to solidification interface velocity v < 0.07 m/s. Consequently, formation of pro-eutectic micro-constituent was suppressed, and RS microstructure formation was dominated by eutectic, α-cell, and banded morphology grains for the Al-20at.%Cu alloy. Eutectic growth operated for interface velocity of 0.1 m/s ≤ v < 0.3 m/s, with a transition from regular lamellar, 2-λ and 1-λ mode to a dense irregular morphology dominated by α-phase at v = 0.3 m/s. Interface temperature calculations indicated feasibility of α-cell growth mode for 0.3 m/s ≤ v < 0.7 m/s. Banded growth occurred for 0.7 m/s ≤ v < 1.3 m/s. Plane front α-phase growth was evident for interface velocities v ≥ 1.3 m/s. Previous work on rapid solidification microstructure development in hypereutectic Al-Cu alloys reported a regime of α-cell growth subsequently to eutectic and prior to transition to banded growth for Al-19at.%Cu (36 wt.%Cu), while for Al-22at.%Cu (40 wt.%Cu) eutectic growth transitioned directly to α-plane front growth without emergence of a banded regime. Based on the current study the disappearance of the banded growth regime occurs for a composition larger than 20at.%Cu.

Effect of laser oscillation and beam incident angle on porosity in double-sided filler welding of 2219 aluminum alloy T joint

In the current research, the double-sided laser beam oscillation filler welding (DLBOW) with beam incident angle from 20° to 40° were carried out for 2219 Al-Cu alloy T joint welding. Double-sided laser beam filler welding (DLBW) was conducted as a reference group. 3D computed tomography (CT) scanning analysis method was performed to investigate the precise three-dimensional locations of the porosity defects in the T joints. High-speed photography was conducted to evaluate the keyhole stability. The dynamic behavior of keyhole of DLBW and DLBOW was simulated by Flow-3D to study the formation process of pores. The effects of beam oscillation and beam incident angle on the macrostructure, microstructure, porosity, and mechanical property of T joints were discussed. It was found that beam oscillation and smaller beam incident angle promoted porosity suppression. The mechanical properties of T joints were improved by laser oscillation. With the beam incident angle of 20°, the porosity of T joint welded by DLBOW was lowest (0.26 %). The hoop tensile strength and T-pull tensile strength of the T joint were 403 MPa and 302 MPa, approximately 89.5 % and 71.6 %, in contrast with that of the base metal.

Experimental determination of solid-liquid interface energy for para- and diamagnetic solid solution in equilibrium with eutectic liquid under a high magnetic field

The solid-liquid interface energy (SLIE) of the Al-Cu and Bi-Cd systems under a high magnetic field (HMF) has been experimentally determined by a Bridgeman-type directional solidification furnace. The equilibrated grain boundary groove shapes for the paramagnetic solid α-Al solution and the diamagnetic solid Bi solution in equilibrium with the eutectic liquid under various HMFs were observed in Al-15.3at%Cu alloy and Bi-50at%Cd alloy. It can be found that the profiles of grain boundary grooves changed significantly under the action of the HMF. The Gibbs-Thomson coefficient and the SLIE for the solid α-Al and solid Bi solution in equilibrium with the eutectic liquid under various HMFs were obtained from obtained grain boundary groove shapes. The results show that the SLIE of the Al-Cu and Bi-Cd alloys increase and decrease under an HMF, respectively. The interaction theory of magnetic dipoles induced by an HMF can be responsible for the above experimental phenomena. Additionally, the results of the differential thermal analysis (DTA) and theoretical analysis indicate that the undercooling of the Al-15.3at%Cu and Bi-50at%Cd alloys increase and decrease under the influence of an HMF, respectively, which is ascribed to the existence of HMF-induced interface energy.

Atomistic insight into dendrite growth orientation transition in Al-Cu alloy

In this study, we investigate the impact of solid-melt interfacial energy anisotropy on the microstructure of components. Our focus is on the Al-Cu system's Al-rich side, where we compute the solid-melt interfacial free energy and its anisotropy using Molecular Dynamics (MD) simulations. Our findings reveal that, as the Cu concentration in the melt increases, the preferred dendrite growth orientation shifts from <100> to <110>. Furthermore, atomic density profile analysis shows an improvement in ordering in the (110) plane at higher Cu concentrations. Our results suggest that the transition in dendrite growth orientation is a consequence of the weakened anisotropy between (100) and (110) interfacial energies at higher Cu concentrations and undercooling temperatures. We also observe displaced atomic density profiles between Al and Cu atoms in proximity to the interface. We propose that a displaced atomic density profile between solute and solvent atoms could be a characteristic feature of systems undergoing a dendrite orientation transition.

Ultrahigh grain boundary strengthening ability of VCoNi medium entropy alloy

Tensile tests of VCoNi medium-entropy alloy with different grain sizes were conducted at 77 K, 194 K and 293 K. The results show that the grain boundary strengthening ability characterized by the Hall-Petch slope of the alloy increases with decreasing temperature and is evidently higher than that of FCC pure metals, CuAl alloys, and some common FCC high-entropy alloys/medium-entropy alloys at room temperature. A new model correlated to intrinsic stacking fault energy and lattice friction stress is derived to describe the high grain boundary strengthening ability. The high grain boundary strengthening ability and its temperature dependence of the VCoNi medium-entropy alloy are mainly attributed to the high lattice friction stress of the VCoNi alloy. The findings provide a possibility for designing the single-phase FCC medium-entropy alloy with ultra-high yield strength and considerable plasticity.

Numerical/Experimental Study of Process Optimization Conducted on an Al-Cu Alloy Produced by Combined Fields of Applied Pressure and Ultrasonic Vibration

Single-pressure and ultrasonic action have their own unique advantages in the treatment of metal melts. When the two are combined into a composite field, the advantages of a single physical field can be fully utilized. So, the cavitation and acoustic streaming effects characteristics of an Al-5.0Cu alloy treated under different coupling process parameters, related to applied extrusion pressure and ultrasonic vibration, were analyzed by combining numerical simulation and experimental verification. The simulation results were experimentally verified by quantitative analysis of the microstructure, the melt, and its macro characteristics. The results show that the closing time t decreases with an increase in the extrusion pressure. In addition, when the ultrasonic power and extrusion force are increased simultaneously (100 MPa and 1 kW), the average grain size and the proportion of columnar grains reach the ideal effect. The influence of pressure parameters is greater, which will also lead to an increase in the proportion of columnar crystals. By optimizing the parameters, the grain size can be further reduced, the proportion of columnar crystal structure can be reduced, and fine and uniform equiaxed crystal structures can be easily obtained.

Mirrored symbols, opposite effects: Impact of Ga and Ag additions on the martensite decomposition of the Cu81Al19 alloy

Although the presence of martensite is desirable in several applications of increasingly complex Cu-rich Cu-Al alloys, there is a lack of understanding about the effects of alloying in its stability. Martensite decomposition was investigated in as-quenched Cu81Al19, Cu79Al19Ga2, and Cu79Al19Ag2 alloys (compositions in atomic percentage) by optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, differential scanning calorimetry, and Vickers microhardness measurements. It was found that the similarity of crystalline structure between alloying element and host phase, as well as the interactions between ternary addition atoms and Al interfere with the stages of the martensite decomposition during heating. The Ga addition refined the microstructure, resulted in the precipitation of other phases, and favored the eutectoid reaction in the Cu81Al19 alloy. The Ag addition increased the tendency for martensite ordering, stabilized the β1 phase, and induced the precipitation of Ag particles from martensite on heating. Possible technological consequences arising from these results were also discussed.

Dendrite operating state in directional solidification of AlCu binary system: numerical benchmark test with the OpenPhase software

A scientific benchmark test is carried out for a multi-phase-field model with double-obstacle potential by performing three-dimensional simulations of dendritic growth under directional solidification. The effects of key numerical parameters of the multi-phase-field model such as numerical resolution and interface width on the dendrite tip operating state are studied, optimal parameter values are set, and where the operating state becomes independent of varying these parameters is elaborated. Some uncertainties in the proper choice of effective interface mobility in the thin-interface limit are discussed and a pragmatic solution is adopted. The binary alloy Al-Cu with 4 at.% Cu is chosen as the material system because it has been used in many previous experimental and numerical studies to investigate dendrite morphology under directional solidification. The recently developed sharp phase-field model by Finel and colleagues is adapted to the double-obstacle potential function and included in the benchmark test. It is shown how the sharp phase-field model helps in achieving agreeable convergence with larger discretization, thereby reducing the computational cost significantly. The benchmarks are performed using the OpenPhase software.

Influence of the iron additive on the microstructural behavior of an aluminum-copper foundry alloy B206

Although used and studied since the beginning of the century, the mechanical properties of aluminum-based structural hardening alloys still conceal some secrets that metallurgists are trying to uncover. In this work we are interested in aluminum alloys and more particularly in an Al-Cu alloy. The main objective of this work was to study the influence of structural hardening heat treatments on the evolution of the mechanical and structural properties of B206 alloys. For that, we used several experimental methods adapted to this kind of scientific work. We quote essentially: the thermal treatments of setting in hardening, as well as measurements of the hardness. The analysis of the experimental results obtained by these methods allowed us to explain and to affirm that Al-Cu alloys do not give appreciable structural hardening; because of the difficulty of diffusion of iron and silicon which influences the treatment and brought in a general way to the precipitation of the phase β; plays an important role in the evolution of the mechanical characteristics of Al-Cu alloys.

Aluminum alloy W-temper cryogenic forming with enhanced formability and strength

Simultaneously obtaining excellent formability and post-form strength in the traditional sheet metal forming of heat-treatable aluminum alloy is challenging, owing to the coexistence of wrinkling and splitting defects during forming and the control problem of microstructure. To solve these problems, W-temper cryogenic forming was proposed based on the cryogenic ‘dual-enhancement effect’ of an as-quenched (W-temper) aluminum alloy. The effects of the cryogenic temperature gradient and blank-holder force on the drawing behaviors were studied by analyzing the forming defects and thickness distribution. Strength distributions were reflected through Vickers hardness measurements under different aging conditions. The related strengthening mechanism was revealed through microstructure characterization. The drawability can be significantly improved at small or large cryogenic temperature gradients. An Al-Cu alloy semispherical shell component was fabricated via W-temper cryogenic forming. The depth of the formed hemispherical specimens increased by more than 106.4%. Uniform thickness can be also obtained at the temperature gradient of 216 °C, with an average thickness deviation rate of 6.5%, benefiting from the cryogenic dual enhancement effect and enlargement of the stress gradient. The hardness in all regions was higher than 146.5 HV of traditional T8-temper because of the enough accelerating precipitation of θʺ and θʹ phases by prior cryogenic deformation. Strain and precipitation strengthening were the main strengthening mechanisms under post-forming and post-aging conditions, respectively. The peak-aging time can be shortened to 6 h, which is one-third that of the traditional process. Enhanced formability and post-form strength can be simultaneously obtained by W-temper cryogenic forming, which has great potential for the fabrication of thin shells made from heat-treatable aluminum alloys.

Sn-induced phase transformation mechanism from θ’ to θ in Al-4Cu alloy and its influence on high temperature strength

The effects of 0.02 wt.% Sn addition to Al-4Cu alloy on the phase transformation mechanism from θ’ to θ phase during a long-time heat exposure at 573 K for 100 h and on high temperature strength were studied through microstructure observation and tensile test. It is found that Sn micro-alloying in Al-4Cu alloy completely changes the mechanism of θ’ → θ phase transformation during the long-time heat exposure. In the alloy without Sn addition, rod-like θ phase nucleates and grows on the surface of coarsened disc-like θ' phase. However, with Sn-micro-alloying, θ phase firstly heterogeneously nucleates on β-Sn particles, and then grows into much coarser needle-like phase. Trace addition of Sn significantly increases the yield strength of T5-samples at both room temperature and 573 K, because addition of Sn increases the number density of θ’ particles and reduces its size. But, after the long-time heat exposure, the high temperature (573 K) strength of Al-4Cu alloy is severely degraded because Sn accelerates the phase transformation from θ’ to θ phase.

Tailoring the mechanical properties and thermal stability of additive manufactured micro-alloyed Al-Cu alloy via multi-stage heat treatment

In this study, a novel Sc/Zr/Ti/Er-modified 2219 aluminum alloy was designed and wall-shaped components were then fabricated by wire-arc directed energy deposition (DED). Due to the heterogeneous nucleation promoted by primary Al3X dispersoids, the as-deposited alloy exhibits a highly equiaxed fine grain structure. Two heat treatment schedules were conducted to tailor the strength and thermal stability of the alloy. Compared with the classical T6 heat treatment, the additional homogenization step before the T6 heat treatment (HT6) prefabricated more Al3X dispersoids, which indirectly promoted the transition from θ″ precipitates to θ′ precipitates, resulting in a slight reduction in strength. However, this homogenization step helps to avoid the aggregation of pores by promoting pores ripening and significantly alleviates the anisotropy of ductility. In addition, the better thermal stability of the HT6 heat treated alloy is due to more Al3X dispersoids and finer θ′ precipitates with high coarsening resistance caused by the segregation of Sc and Mn at the θ′/Al interface during thermal exposure. In general, the wire-arc DEDed micro-alloyed 2219 Al alloy exhibits a promising combination of strength and ductility after heat treatment and its mechanical properties are superior to those of the wrought micro-alloyed Al-Cu alloys.

Parameters prediction in additively manufactured Al-Cu alloy using back propagation neural network

The relationship between tensile strength, wire feeding speed and travel speed is built based on Back Propagation (BP) neural network during the wire arc additive manufacturing (WAAM) process. The introduction of a genetic algorithm for optimising the BP neural network (GA-BP) and incorporation of additional parameter combinations through the forward model markedly enhance the prediction accuracy of the process parameter reverse model. The BP neural network with a genetic algorithm model exhibits excellent training results, and the sample population regression reaches 0.97. An error value of the optimised model is only 3.10% for wire feeding speed prediction, only 1.55% for travel speed prediction. The GA-BP reverse model optimises WAAM process parameters and achieves a tensile strength exceeding 230 MPa.

Strength and stability through variable micro segregation behaviour of Ta and Zr solutes at intermetallic interfaces in Al-Cu alloys

A small amount of Zr and Ta are added to aluminium-copper (Al-Cu) alloys, and the evolution of strengthening phases with multi-step heat-treatment and their stability after prolonged thermal exposure at 250 °C has been studied. The L12 ordered (Al,Cu)3(Zr,Ta) precipitates were formed in the Al-matrix, followed by preferential nucleation of Cu-rich θ"/θ' plates on the L12/matrix interfaces. Transmission electron microscopy and atom probe tomography studies established the segregation of Zr and Ta at θ' plate/matrix in the aged alloys. It is shown that Zr segregates at coherent broad interfaces of θ' plate and inhibits the growth of these interfaces. Segregation of Ta primarily occurs at the growing θ' plate interface in the lengthening direction (semi-coherent interface) along with Zr and restricts the lengthening of the plate. The restricted growth triggers sympathetic nucleation of newer plates at the plate edges to sustain the growth process. A yield strength of ∼475 MPa at room temperature is recorded due to the presence of ordered precipitates and the growth restriction of θ' plate. Segregation of slow diffusing elements (Zr and Ta) also enhances the thermal stability of the microstructure.

Tissue evolution of Al0.67Cu0.33 alloy during melting and solidification by molecular dynamics simulation

To analyze the various factors affecting the solidification organization of Al-Cu alloys, the melting and solidification processes of Al0.67Cu0.33 alloy were simulated by the embedded atomic method (EAM) potential. It is found that the diffusion coefficient of the system keeps rising with the increasing initial temperature and relaxation time. It is a positive correlation between initial temperature, relaxation time and diffusion coefficient. The RDF analysis results are shown that as the cooling rate decreases, the crystal content of the solidified tissue increases and crystal structure characteristics of the system become more obvious. At the cooling rate of 1 × 1010 K/s, the percentage of system crystal compositions reaches 78.4%. The system shows obvious crystal structure characteristics. However, when the cooling rate was 1 × 1014 K/s, the crystalline content of the system is only 0.3% and shows obvious non-crystalline characteristics. It provides a theoretical basis for improving the properties and optimizing the microstructure of Al-Cu alloy.

Quantitatively Comparing 3D Discrete Element Method Simulations With Drained Compression Experiments of the Semi-solid Deformation of Al-Cu Alloys

Quantitatively Comparing 3D Discrete Element Method Simulations With Drained Compression Experiments of the Semi-solid Deformation of Al-Cu Alloys