Al-Zr Alloys Research Articles

Thermal stability of microstructure and properties of ingots and fine wires from Al–Zr alloys

The process of precipitation of Al3Zr particles in cast Al–(0.25–0.4) wt % Zr alloys manufactured by the induction casting method is studied. The effect of zirconium concentration on the microstructural parameters, hardness, and specific electrical resistance (SER) of cast alloys is investigated. The dependences of hardness and SER on the time of cast alloys annealing at 500°C are plotted. The parameters of the Johnson–Mehl–Avrami–Kolmogorov equation for alloys with different Zr content are determined. The optimal regimes of cast ingot aging are found. Fine wires with ∅ 0.3 mm are manufactured by the drawing method; their strength, SER, and hardness are studied in the initial state and after heat treatment. The tests of thermal stability of wires are carried out according to the state standard GOST R MEK 62004–2014.

Potentiostatic electrolysis of fluoride melts with zirconium oxide additives

Currently, the demand for zirconium-based alloys and materials is growing significantly due to their high thermal and corrosion resistance combined with mechanical strength. Existing technologies for producing zirconium and its alloys are complicated by the high temperature of the process, or labor intensity and multi-stage nature, which significantly increases the cost of the target material up to the loss of profitability of the process. Electrochemical synthesis of zirconium and its alloys in fluoride-based melts, using zirconium oxides as the main metal-containing consumable component, seems more profitable. In this work, a series of electrolysis tests were carried out to deposit Al-Zr alloy at a potential of 1.6 V on graphite and molybdenum cathodes. According to the previously obtained results, in the presence of ZrO2 in the KF-AlF3-Al2O3 melt, a plateau and a discharge peak of electroactive ions appear on the cathode branch of the voltammograms at potentials of -1.4 and -1.7 V, ZrI and ZrII, respectively. Similar responses appear on tungsten at potentials of -1.3 and -1.6 V, respectively, and in the potential region of -1.9 V there is a clear peak (Al) of electroreduction of aluminum ions. As a result of electrolysis, it was found that the graphite anode was consumed, and a fairly well-bonded deposit was formed on the cathode. Part of the cathode deposit was mechanically separated from the cathode for analysis of its chemical and phase composition. Based on the results of X-ray phase analysis, it was found that the cathode deposit mainly consists of Al3Zr and aluminum compounds with molybdenum impurities, with the composition Al12Mo, which is consistent with known ideas about the formation of intermetallic compounds during the interaction of aluminum with other metals. Electrolysis of the melt on the graphite cathode was carried out under similar conditions. Based on a microphotograph of the cathode cross section, it was found that during electrolysis, a layer of deposit containing both zirconium and aluminum was formed at the electrode-electrolyte phase boundary.

Exploring the local structure of molten Al-Zr-Y(Si) alloys using ab initio molecular dynamics

Accelerating the diffusion rate of Zr in aluminum and suppressing Zr segregation during solidification are crucial for enhancing the heat resistance of Al-Zr alloys. In this study, ab initio molecular dynamics simulations were employed to investigate the local structure of molten Al-Zr-Y(Si) alloys and the morphology of the liquid/substrate interface. By examining the atomic interactions, the mechanism by which Si addition improves Zr segregation during solidification and accelerates Zr diffusion was revealed. The results indicate that the interaction between Si and Zr is significantly stronger than that with other alloying elements such as Al, Y, and Zr itself. The introduction of Si had a discernible detrimental effect on Zr-Zr bonds, as Zr atoms exhibited a preference for bonding with Si atoms, consequently promoting cluster formation. This phenomenon resulted in the fragmentation of large Zr clusters into smaller ones. Moreover, the inclusion of Si atoms notably augmented the diffusion coefficient of Zr atoms within the Al-Zr-Y alloy. Analysis of the solid-liquid interface unveiled a noteworthy dragging effect, where Si atoms prominently pulled Zr atoms into the liquid phase at the interface's forefront.

Effect of Er on Microstructure, Electrical Conductivity, Mechanical Properties, and Corrosion Resistance of an Al-Zr Alloy

Effect of Er on Microstructure, Electrical Conductivity, Mechanical Properties, and Corrosion Resistance of an Al-Zr Alloy

Coupling Effect of Mn Addition and Deformation on Mechanical and Electrical Properties of Al-Zr Alloys

In order to increase the strength of Al-Zr alloys, which are promisingly used for heat-resistant conductors, the coupling effect of Mn addition (0.16 wt.% and 0.88 wt.%) and deformation on the precipitation, mechanical, and electrical properties of an Al-0.18wt.% Zr alloy was studied using transmission electron microscopy (TEM), atom probe tomography (APT), hardness testing, and electrical conductivity measurement, respectively. Results showed that the Mn addition fully suppresses the Al3Zr precipitation in both hot-deformed and undeformed cases, which is mainly due to a strong Mn-vacancy bonding, in which Mn atoms seize vacancies and hence reduce the available vacancies for Al3Zr nucleation. Minor 0.16 wt.% Mn addition causes a simultaneous decrease in hardness and electrical conductivity, regardless of whether there is deformation. The higher 0.88 wt.% Mn addition, however, significantly increases the hardness by over 40%, especially in combination with deformation. Possible influencing factors such as grain size, dislocations, intergranular/intragranular precipitation, and solute clusters are comparatively discussed in terms of microstructural features and mechanical/electrical properties that are tuned by Mn addition and/or deformation. It is found that the Mn addition can make remarkable contributions to the hardness and thermal stability of the Al-Zr alloys when coupled with deformation.

Influence of alloying parameters on the structure and properties of AK-6 aluminium alloy

This work is devoted to the study of the effect of zirconium addition and crystallization rate on the structure and properties of industrial aluminium alloys. Experimental alloying of the AK6 alloy was performed. The required amount of Al-Zr-10 alloy (10 wt. % Zr) was added at a temperature of 900 °C until the zirconium content in the target alloy reached 0.1; 0.3; 0.5 wt. %. According to the results of scanning electron microscopy and X-ray diffraction analysis, the main proportion of zirconium in the initial alloy was represented by intermetallic compounds of predominantly Al3Zr composition and sizes from 5 to 50 μm. Values of microhardness measured after direct alloying of high-purity aluminum with zirconium by the electrolysis of oxide-fluoride melts demonstrate that at a zirconium content of 0.4 wt. %, the microhardness of the alloy increases by 1.5 times and continues to grow as the zirconium content increases. Based on the results of structural analysis, it was found that the average grain size of the aluminium alloy decreased by 4–5 times even at a Zr content of 0.1 wt. %. When studying the properties of the obtained samples, it was found that the addition of zirconium to the AK6 alloy does not affect its hardness, in contrast to high-purity aluminium, which is presumably due to the more pronounced influence of other components and the absence of an additive effect of zirconium on the alloy hardness. Accelerated cooling of the alloy to 103 K/s without zirconium additives has a similar effect of grain reduction, and also increases the microhardness of the alloy by 10 HB according to Brinell. A study of the combined effect of zirconium addition and accelerated cooling shows the additive effect of grinding by more than 25 times, while individual grains do not exceed 5 microns in size. The absence of intermetallic compounds in the obtained samples of the AK6 alloy after modification with the Al-Zr alloy indicates that the phase composition of the initial Al-Zr alloy does not affect the properties of the target alloys.

A high strength Al-Zr alloy with good electrical conductivity by combining gas-assisted continuous casting and extrusion with subsequent thermomechanical treatment

A high strength Al-Zr alloy was prepared based on a novel technique called gas-assisted continuous casting and extrusion (GAC). Results show that the solid solubility of Zr in the Al matrix could be increased due to the non-equilibrium solidification during the GAC process. After aging treatment (350 °C/275 h), the alloy has excellent combined properties (tensile strength and electrical conductivity of 200 MPa and 59.6% IACS, respectively); after cold drawing (94% deformation), the alloy can have tensile strength up to 278 MPa and good electrical conductivity (55.2% IACS). The GAC technology can fabricate aluminum alloy rod with higher solid solubility of Zr in a single-step operation, which is expected to be applied to the efficient preparation of high performance Al-Zr alloy wires.

A Molecular Dynamics Simulation to Shed Light on the Mechanical Alloying of an Al-Zr Alloy Induced by Severe Plastic Deformation

In a recent experimental work, as a result of severe plastic deformation, a non-equilibrium solid solution was obtained despite the very limited solubility of zirconium (Zr) in aluminum (Al). This opens up a new path in the development of heat-treatable alloys with improved electrical and mechanical properties, where mechanically dissolved elements can form intermetallic particles that contribute to precipitation strengthening. In the present study, molecular dynamics simulations were performed to better understand the process of mechanical dissolution of Zr within an Al model, with Zr atoms segregated along its grain boundaries. Stress–strain curves, radial distribution functions, and mechanisms of plastic deformation and dissolution of Zr in Al were analyzed. It is revealed that orientation of the grain boundary with segregation normal to the shear direction promotes more efficient mixing of alloy components compared to its parallel arrangement. This happens because in the second case, grain boundary sliding is the main deformation mechanism, and Zr tends to remain within the interfaces. In contrast, the involvement of dislocations in the case of normal orientation of grain boundaries with Zr segregation significantly contributes to deformation and facilitates better dissolution of Zr in the Al matrix. The findings obtained can provide new insights considering the role of texture during mechanical alloying of strongly dissimilar metals.

Diffusion, atomic transport, and ordering in Al-Zr alloys: FCC and liquid phases

Additive manufacturing of materials with controlled microstructure demands knowledge of atomic scale properties near the solid-liquid transition state. Many of these properties are not affordable by experimental techniques and computer modeling is the possible solution to the problem. In this paper, we present the results of an extended atomistic study of intrinsic atomic transport due to vacancy diffusion in FCC and L12 solid phases and diffusion in the liquid phase of Al-Zr alloys. A deceleration of the overall self-diffusion was observed when Zr was added to Al. The effect was stronger in the solid and weaker in the liquid. Additionally, the effect was strongly temperature dependent in the solid phases, but not in the liquid. Atomic transport was chemically biased: transport of Zr atoms was significantly slower than that of Al atoms, and this bias effect was stronger in the solid phases. The overall diffusion and chemical ordering processes in the liquid state were five to six orders in magnitude faster than in the solid. Chemical short-range order parameters in the liquid saturated at values close to those in the ordered L12 structure of Al3Zr. Chemical and structural ordering in the solid phases was negligible over the modeled microsecond time scale. The results are discussed in view of optimizing additive manufacturing parameters for the controlled formation of metastable L12 precipitates.

Electrochemical behavior of Zr(IV) and co-reduction synthesis of Al-Zr alloys in KF-AlF3-Al2O3-ZrO2 molten salt

Electrochemical behavior of Zr(IV) and co-reduction synthesis of Al-Zr alloys in KF-AlF3-Al2O3-ZrO2 molten salt

Diffusion controlled early-stage L12-D023 transitions within Al3Zr

Antiphase boundary (APB) in Al3Zr was regarded to play an important role in the L12-D023 phase transition, the formation of which has long been explained through the shearing/slipping mechanism. Herein, the detailed atomic structures of conservative {100} APBs within L12-Al3Zr particles forming at the early-stage of L12-D023 transition in an Al-Zr alloy were systematically studied by high angle annual dark-field scanning transmission electron microscope (HAADF-STEM). As a strong evidence of diffusion-limited phase transformation process, significant de-ordering of atoms in APBs and the neighboring atomic planes have been found. By analyzing the two possible pathways, it is suggested that L12-D023 phase transition has been achieved through a diffusion mechanism, instead of shearing mechanism while the formation of APB is an intermediate stage of the phase transition process. First principles density functional theory (DFT) reveals that the formation of APBs and subsequent phase transition are energetically favorable, which provide the driving force for diffusion.

Assessing Strain Rate Sensitivity of Nanotwinned Al–Zr Alloys through Nanoindentation

Nanotwinned metals have exhibited many enhanced physical and mechanical properties. Twin boundaries have recently been introduced into sputtered Al alloys in spite of their high stacking fault energy. These twinned Al alloys possess unique microstructures composed of vertically aligned Σ3(112) incoherent twin boundaries (ITBs) and have demonstrated remarkable mechanical strengths and thermal stability. However, their strain rate sensitivity has not been fully assessed. A modified nanoindentation method has been employed here to accurately determine the strain rate sensitivity of nanotwinned Al–Zr alloys. The hardness of these alloys reaches 4.2 GPa while simultaneously exhibiting an improved strain rate sensitivity. The nanotwinned Al–Zr alloys have shown grain size-dependent strain rate sensitivity, consistent with previous findings in the literature. This work provides insight into a previously unstudied aspect of nanotwinned Al alloys.

Effect of Sc, Hf, and Yb Additions on Superplasticity of a Fine-Grained Al-0.4%Zr Alloy

This research was undertaken to study the way deformation behaves in ultrafine-grained (UFG)-conducting Al-Zr alloys doped with Sc, Hf, and Yb. All in all, eight alloys were studied with zirconium partially replaced by Sc, Hf, and/or Yb. Doping elements (X = Zr, Sc, Hf, Yb) in the alloys totaled 0.4 wt.%. The choice of doping elements was conditioned by the possible precipitation of Al3X particles with L12 structure in the course of annealing these alloys. Such particles provide higher thermal stability of a nonequilibrium UFG microstructure. Initial coarse-grained samples were obtained by induction casting. A UFG microstructure in the alloys was formed by equal-channel angular pressing (ECAP) at 225 °C. Superplasticity tests were carried out at temperatures ranging from 300 to 500 °C and strain rates varying between 3.3 × 10−4 and 3.3 × 10−1 s−1. The highest values of elongation to failure are observed in Sc-doped alloys. A UFG Al-0.2%Zr-0.1%Sc-0.1%Hf alloy has maximum ductility: at 450 °C and a strain rate of 3.3 × 10−3 s−1, relative elongation to failure reaches 765%. At the onset of superplasticity, stress (σ)–strain (ε) curves are characterized by a stage of homogeneous (uniform) strain and a long stage of localized plastic flow. The dependence of homogeneous (uniform) strain (εeq) on test temperature in UFG Sc-doped alloys is increasing uniformly, which is not the case for other UFG alloys, with εeq(T) dependence peaking at 350–400 °C. The strain rate sensitivity coefficient of flow stress m is small and does not exceed 0.26–0.3 at 400–500 °C. In UFG alloys containing no Sc, the m coefficient is observed to go down to 0.12–0.18 at 500 °C. It has been suggested that lower m values are driven by intensive grain growth and pore formation in large Al3X particles, which develop specifically at an ingot crystallization stage.

Ternary Diffusion and Thermodynamic Interaction in the β Solid Solutions of Ti–Al–Zr Alloys at 1473 K

Interdiffusion in Ti-rich β solid solutions in Ti–Al–Zr alloys was investigated at 1473 K. In the β Ti–Al–Zr alloys, the main interdiffusion coefficients (i.e., and , respectively) and the cross interdiffusion coefficients, (i.e., and , respectively) have positive values, as well as a slight concentration dependence. The values of are larger than those of . In Ti–Al–X (= V, Cr, Fe, Co, Zr) alloys, the values of the main coefficients are at 1473 K. Repulsive interactions occur between Al and X (= V, Cr, Fe, Co, Zr) atoms in the Ti–Al–X alloys, because the ratio values of the cross coefficients to the main ones are positive in sign. On the other hand, the interactions between Ti (solvent) and X (= V, Cr, Fe, Co, Zr) (or Al) atoms are attractive in the present alloys because the ratio of the converted interdiffusion coefficients is negative values.

Influence of Decreased Temperature of Tensile Testing on the Annealing-Induced Hardening and Deformation-Induced Softening Effects in Ultrafine-Grained Al-0.4Zr Alloy.

The influence of decreased temperature of tensile testing on annealing-induced hardening (AIH) and deformation-induced softening (DIS) effects has been studied in an ultrafine-grained (UFG) Al-Zr alloy produced by high-pressure torsion. We show that the UFG Al-Zr alloy demonstrates a DIS effect accompanied by a substantial increase in the elongation to failure δ (up to δ ≈ 30%) depending on the value of additional straining. Both the AIH and DIS effects weaken with a decrease in the tensile test temperature. The critical deformation temperatures were revealed at which the AIH and DIS effects are suppressed. The activation energy Q of plastic flow has been estimated for the UFG Al-Zr alloy in the as-processed, subsequently annealed and additionally strained states. It was shown that the annealing decreases the Q-value from ~80 kJ/mol to 23-28 kJ/mol, while the subsequent additional straining restores the initial Q-value. Alloying with Zr results in the expansion of the temperature range of the AIH effect manifestation to lower temperatures and results in the change in the Q-value in all of the studied states compared to the HPT-processed Al. The obtained Q-values and underlying flow mechanisms are discussed in correlation with specific microstructural features and in comparison to the UFG Al.

Effect of Sc and Zr on microstructure and chemical milling surface roughness of 2024-T6 alloy sheets

Chemical milling is one of the most widely used processing methods for Al alloys in the aerospace and aircraft industries. The surface roughness significantly impacts the mechanical performance of chemically-milled products. Therefore, it is rational to develop a strategy to control the surface roughness. In this study, the effect of minor Sc and Zr additions on the microstructure and chemical milling surface roughness of a 2024-T6 alloy sheet was investigated. The additions optimized the surface roughness, and values of (0.7377 ± 0.0024) and (0.9053 ± 0.0018) μm in the rolling and transverse directions respectively, were achieved, which were significantly lower than those achieved by the 2024 alloy ((1.0785 ± 0.0026) and (1.2205 ± 0.0021) μm, respectively). The 2024SZ (2024-0.1Sc-0.2Zr Al) alloy exhibited fine and discontinuous grain boundary intermetallic particles (IMPs) in the as-cast state. Thermo-Calc software showed that the 2024 SZ alloy formed L12-Al3(Sc, Zr) phases during solidification, which induced heterogeneous nucleation and refined the grains. The weight fraction of IMPs in the 2024SZ alloy was much considerably smaller than that in the 2024 alloy during solidification. These IMPs affected the density of the IMPs in the T6 state. Finally, the mechanism of Sc and Zr on the chemical milling surface roughness of the 2024-T6 alloy was demonstrated. This study provides a feasible strategy for optimizing the chemically-milled surface roughness of Al alloys.

Exploring the deformation behavior of nanotwinned Al–Zr alloy via in situ compression

Nanotwinned metals have demonstrated the capacity for concomitant high strength and ductility. However, metals with high stacking fault energies, such as aluminum (Al), have a low propensity for twin formation. Here, we show the fabrication of supersaturated solid-solution Al–Zr alloys with a high density of growth twins. Incoherent twin boundaries (ITBs) are strong barriers to dislocation motion, while mobile partial dislocations promote plasticity. These deformable nanotwinned Al–Zr alloys reach a flow stress of ∼1 GPa, as demonstrated using in situ micropillar compression tests. Density functional theory calculations uncover the role Zr solute plays in the formation and deformation of the nanotwinned microstructure. This study features a strategy for incorporating ITBs and 9R phase into Al alloys for simultaneous benefits to strength and deformability.

Zr-Al 16 wt. % and Na2CrO4 composite particles used for Na dispenser and its reaction kinetic

An alkali metal dispenser is the core device for vacuum evaporation in producing multialkali photocathodes. However, the reaction kinetic of alkali metal chromate being reduced by a Zr-Al alloy, which is the most commonly used alkali metal dispenser, has not been reported. In this work, we made composite particles of Zr-Al 16 wt. % powders with Na2CrO4 by a method of liquid precipitation. Through thermal analysis of its reaction, we found that the difference of a Zr-Al particle size would affect the reaction starting temperature but would not make a significant difference on the apparent activation energy. Through the comparison method by Sharp, we found that the 3D Avrami–Erofeev equation fits for this reaction and established a reaction degree-temperature function, and the reaction kinetic was further verified by a vacuum evaporation experiment. Through an in situ XRD measurement, the chemical change during an Na dispenser’s working process is found to be Na2CrO4 → Na2CrO4, Na2CrO3, and Cr2O3 coexist → NaCrO2. This work may serve as a reference for the design of alkali metal dispensers and help to improve the control precision for an evaporation process.

Quasi in-situ analysis of compressive creep behaviors and microstructure evolutions in Al–Zr alloys with Sc and Er additions

Al–Zr series alloy wires are not in a state of constant temperature and stress during service, thus the compressive stress and aging effects on the creep response in a changing state should be clarified. In this study, the quasi in-situ compressive creep behaviors and microstructure evolutions of Al–Zr alloys with Sc and Er additions have been studied. It is found that CCA curves of Al–Zr alloy were severely deformed at 120 °C for 40 h/90 MPa, for Al–Zr–Er alloy, the CCA curves sharply increased at 150 °C for 40 h/90 MPa, and that of Al–Zr-Sc alloy always kept stable at different stages. Moreover, different creep mechanisms were found in these alloys. After different CCA stages, the fibrous grains are always existing in the Al–Zr-Sc alloy, while equiaxed grains appear in the Al–Zr and Al–Zr–Er alloys, indicating the better compressive creep resistance with Sc additions. Discontinuous dynamic recrystallization (DDRX) is the dominant nucleation mechanism in the three alloys, and secondary dynamic recrystallization (SDRX) is the subordinate nucleation mechanism for the Al–Zr and Al–Zr–Er alloys. Additionally, Sc rich precipitation makes the stacking energy and lattice strain field obviously fluctuate and promotes the effective diffusion and storage of dislocations with Lomer–Cottrell locks, therefore, the compressive creep resistance of the material is improved.

Effect of Heat Treatment on the Mechanical Properties of Ti–Nb–Mo–Zr–Al Alloys

Effect of Heat Treatment on the Mechanical Properties of Ti–Nb–Mo–Zr–Al Alloys