Al-Zr Alloys Research Articles

Spherical Al-Zr alloy powders prepared by centrifugal atomization for tunable energetic behavior

To improve the energetic behavior of Al, heterogeneous Al-Zr alloy powders were prepared by high-speed centrifugal atomization in this paper, the phase composition of which is Al and Al3Zr. The thermal analysis results show that the main oxidation process of Al-Zr occurs at 800 °C–1200 °C. The oxidation peak temperature of the alloy is 25 °C lower than that of Al, accompanied with a higher weight gain and faster oxidation rate. Besides, the activation energy (Ek) is significantly reduced by 74 kJ/mol. Compared with Al/CuO, the ignition delay of Al-Zr/CuO is shortened by 0.6 ms, and the reaction temperature is advanced by 29 °C. This is due to the earlier concentrated heat release of Al3Zr and the grain refinement of Al-Zr that aggravates the shell fracture and result in more intense oxidation of the alloy powders. Therefore, Al-Zr alloy powders possess a significantly enhanced combustion performance than Al.

On the devitrification of Cu–Zr–Al alloys: Solving the apparent contradiction between polymorphic liquid-liquid transition and phase separation

In this work, the crystallization pathways and kinetics of the Cu47.5Zr45.1Al7.4 bulk metallic glass (BMG) are studied systematically using a broad collection of laboratory and synchrotron-based techniques, such as differential scanning calorimetry, transmission electron microscopy, in situ high-energy synchrotron X-ray diffraction (HEXRD), simultaneous small- and wide-angle X-ray scattering, and atom probe tomography. The crystallization sequence during heating at conventional slow rates and isothermal annealing near the glass transition temperature was determined to consist in preferential formation of (Cu, Al)10Zr7 followed by the formation of CuZr2 and AlCu2Zr induced by long-range atomic diffusion. In situ HEXRD shows that the formation of the latter two phases is accompanied by the partial dissolution of the primary Cu-rich phase. Microstructural characterizations of annealed samples suggest that a new liquid phase with enhanced local order and obscure compositional changes has formed from the homogeneous supercooled liquid before crystallization. A concept analogous to the disorder-to-order transition in crystalline materials is applied here to describe the observed transition in liquid, resolving the longstanding apparent contradiction between observing a nanoscale phase separation versus a liquid–liquid phase transition during devitrification. Furthermore, we suggest that the formation of an intermediate liquid phase prior to crystallization is the structural origin of the rapid devitrification kinetics during the primary crystallization. On the basis of our combined experimental results, a scheme is proposed to generalize the complex multistep devitrification mechanisms of the Cu47.5Zr45.1Al7.4 BMG during isothermal annealing or slow heating. This work may provide new insights into the crystallization behavior and thermal stability of Cu–Zr–Al BMGs in terms of thermodynamics and kinetics and might lead to deeper understanding of the underlying mechanisms of the often observed rapid crystallization processes of deeply undercooled metallic liquids.

The growth restriction effect of TiCN nanoparticles on Al-Cu-Zr alloys via ultrasonic treatment

Ex situ and in situ synchrotron X-radiography study on Al-Cu-Zr alloys with addition of Al-5Ti-1B and TiCN nanoparticles (TiCNnp) were carried out at different cooling rates. Al-Zr alloy can be effectively refined by TiCNnp via Ultrasonic treatment as compared with Al-5Ti-1B which has Zr poisoning effect. The influence of cooling rate on the nucleation and growth of grains have been studied quantitatively. The results show that the grain size was decreased and the growth rate was increased with the increasing of cooling rate. At the same cooling rate, the grain size with addition of 0.5% TiCNnp was smaller than that with the same addition of Al-5Ti-1B. The blocking factor f of TiCNnp decreases with increasing cooling rate. Based on the free growth model, a new numerical model considering the growth restriction effect of nanoparticles was established. The growth of grain was inhibited by the combining effect of solute and nanoparticles. The growth rate of grain is reduced due to part of the solid/liquid interface coated by nanoparticles. The blocking factor f is linearly decreased with the coverage ratio ω which is proportional to the critical grain radius. The grain size decreases with increasing cooling rate and decreasing f . This study is especially beneficial for Al alloys that have poisoning phenomenon inoculated by traditional refiner.

Investigations of cathodic reactions using cyclic voltammetry and electrochemical behavior of Ti–Al–Zr alloy in nitric acid using electrochemical impedance spectroscopy

Investigations of cathodic reactions using cyclic voltammetry and electrochemical behavior of Ti–Al–Zr alloy in nitric acid using electrochemical impedance spectroscopy

Decrease in Electrical Resistivity below 28 nΩm by Aging in Hyperperitectic Al-Zr Alloys Treated at High Temperatures

High-voltage and alternating current conductors are mainly made up of a steel core and an envelope made of aluminum wires. The alloys commonly used in the shell are of pure aluminum, which provides low electrical resistivity, but also low mechanical resistance. The correlation between resistance and electrical resistivity has become a design limitation, which limits the development of new alloys. Traditional airline conductors limit their service temperature to a maximum of 80 °C. Al-Zr alloys are susceptible to hardening by aging treatment at high temperatures due to the precipitation of the metastable L12-Al3Zr phase, which allows their working temperature to be limited to 300 °C. This work aims to correlate the resistance and electrical resistivity of two alloys with hyperperitectic compositions, subjected to a solution treatment at 640 °C. At the same time, the aging potential at different temperatures is analyzed using aging duration of up to 900 h. Whereas, the ultimate goal is to correlate the results with electrical resistivity, trying to achieve resistivity values lower than 28 nΩm. It is worth mentioning that there is a slow aging process and the inverse correlation between hardness and electrical resistivity. The optimum result is achieved in an alloy with more than 0.4% Zr subjected to aging at 380 °C in a time range between 425 and 900 h. In these cases, electrical resistivity values lower than 26 nΩm were reached. Transmission electron microscopy (TEM) verified the nanometric size of the L12-Al3Zr precipitates and their coherence with the α(Al) matrix. In turn, the size distribution of the precipitates was analyzed, revealing two different families of precipitates with respective averages of 4 and 19 nm. The precipitates associated with the average of 4 nm are the majority when the aging time is 425 h. However, when the aging time increases to 900 h, sizes close to 20 nm are the majority. This confirms the slow growth of the L12-Al3Zr precipitates during aging and the beginning of the over-aging phenomenon after almost 900 h of aging.

Effect of Boronizing Treatment on the Conductivity of a High-Conductivity and Heat-Resisting Al-Zr Alloy Conductor Material

The effect of boronizing treatment on the conductivity of a high-conductivity and heat-resistant Al-Zr alloy conductor material was studied. The results showed that the conductivity of industrial pure Al containing transition element (Ti, V, Cr, Mn)>0.01 wt % (mass fraction, the same below) was improved to a certain extent by using boronizing treatment to remove transition metal elements through the formation of borides. Using the boronizing treatment, B can react with transition elements to form blocky (Ti, V, Fe)B2and flocculent (Ti, V, Fe, Zr)B2. The boronizing treatment makes Ti and V out of the solid solution state, form borides and finally deposit to the bottom of the furnace, thus significantly improving the conductivity of the ingot. In addition, Cr and Mn were not found in the borides at the bottom of the furnace. However, for the high-conductivity and heat-resisting Al-Zr alloy conductor material, B will have poison effects on Zr during boronizing treatment, thus reducing the heat-resistance of the alloy. Therefore, in the preparation process of high-conductivity and heat-resistant Al-Zr alloy conductor material, the converter process should be added after boronizing treatment to ensure that the Al-Zr alloy conductor material has good heat-resistance and conductivity at the same time.

First-principles calculations to investigate pressure effect on mechanical and thermal properties of ZrAl2

The mechanical and thermal properties of ZrAl2 under high pressure are of great significance in the field of science and engineering technology of Zr-Al Alloys, and are studied by first-principles. The stress dependencies of the elastic and thermodynamic properties of the ZrAl2 were investigated in the ranges of 0 ~ 30 GPa. The result shows that with increasing pressure, the computed elastic constants of ZrAl2 compound increase monotonically, and ZrAl2 is weakly anisotropic. Moreover, ZrAl2 initially appears brittle, but its ductility is significantly improved at higher pressures. ZrAl2 is an indirect bandgap semiconductor under pressures of 5 ~ 10 GPa, but under higher pressure, their valence band overlaps with the conduction band on the Fermi surface. With increasing pressure, a strong covalent feature in the Zr-Al bonds occurs. Besides, the thermodynamic properties of ZrAl2 at higher pressures obtained by calculating the phonon spectrum are discussed. Our findings are useful as a reference for basic studies on the properties of ZrAl2 and for future practical applications of this phase.

Synergistic strengthening by nano-sized α-Al(Mn,Fe)Si and Al3Zr dispersoids in a heat-resistant Al–Mn–Fe–Si–Zr alloy

Strengthening by dispersoids in Al alloys has been limited by either low number density or low volume fraction of dispersoids. In the present work, the influence of an addition of 0.28 wt% Zr on precipitation hardening behavior of AA3003 alloy subjected to different heat treatments has been investigated. A superior microstructure simultaneously consisting of nano-sized α-Al(Mn,Fe)Si and Al3Zr dispersoids at peak-aged state was achieved by two different heat treatment regimes, ramp heating with a speed of 50 °C/h and isothermal aging at 400 °C. As a result, a substantial increase in yield strength of 30 MPa (43%) was achieved in comparison to AA3003 alloy. Meanwhile, the AA3003-Zr alloy exhibits excellent heat-resistance with a stable yield strength from 12h (106 MPa) up to 250h (107 MPa) during isothermal aging at 400 °C. This remarkable thermal stability was ascribed to the continuously hardening from Al3Zr precipitation, which compensates the strength loss from α-dispersoid coarsening. Besides, TEM study shows that the precipitation kinetics of Al3Zr is significantly enhanced compared with the reference binary Al–Zr alloy, which is attributed to the Si content in the alloy. This work proposes an effective method to design a low-cost heat-resistant Al alloy in mass production.

Mechanical Properties of Commercial Purity Aluminum Modified by Zirconium Micro-Additives

The mechanical properties and the fractured surfaces of commercial purity aluminum modified by zirconium micro-additives were investigated by means of experimental examination. A commercial purity Al specimen was used as a reference material and seven Al-Zr alloys in the 0.02–0.14 wt.% Zr composition range (with 0.02 wt.% Zr step) were prepared by microalloying methods. Optical microscopy was used to examine the microstructures and to calculate the grain sizes of the prepared specimens. The phase assemblage diagrams were plotted and the relative amounts of solid phases were calculated at room temperature using FactSage thermochemical software and databases. Proof stress, strength coefficient and strain hardening exponent were measured from the stress-strain curves obtained from tensile experiments and Charpy impact energy was calculated for all specimens. The experiments showed that the grain size of commercial purity Al was reduced by adding any Zr concentration in the investigated composition range, which could be due to the nucleation of new grains at Al3Zr particle sites. Accordingly, the microhardness number, tensile properties and Charpy impact energy were improved, owing to the large grain-boundary areas resulted from the refining effect of Zr, which can limit the movement of dislocations in the refined samples. The basic fracture mode in all specimens was ductile, because Al has an FCC structure and remains ductile even at low temperatures. The ductile fractures took place in a transgranular manner as could be concluded from the fractured surface features, which include voids, ridges and cavitation.

Revealing the univariate effect of structural order on the oxidation of ternary alloys: Amorphous vs. crystalline Cu–Zr–Al alloys

A comparative oxidation study of homogeneous amorphous and crystalline Cu28Zr51Al21 alloys is presented to reveal the univariate role of structural order on the oxidation behavior of multi-component alloys. Amorphous Cu–Zr–Al is confirmed much more oxidation-resistant than crystalline Cu–Zr–Al. Preferential oxidation of Zr and Al occurs in both alloys, resulting in an amorphous Zr–Al–O layer and a Cu-enriched region. Cu-enrichment in the crystalline alloy causes Cu9Al4 nanocrystals embedded in the oxide. However, the Cu-enriched region in the amorphous alloy remains amorphous because of its high glass-forming ability. Findings provide design strategies for achieving highly oxidation-resistant alloys.

The Growth Restriction Effect of Ticn Nanoparticles on Al-Zr Alloys: An Integrated Study by in Situ X-Radiography and Numerical Modeling

Ex situ and in situ synchrotron X-radiography study of Al-Zr alloys with addition of Al-5Ti-1B and TiCN nanoparticles (TiCNnp ) were carried out at different cooling rates. Al-Zr alloy can be effectively refined by TiCNnp as compared with Al-5Ti-1B which has Zr poisoning effect. The influence of cooling rate on the nucleation and growth of grains has been studied quantitatively. The results show that the grain size was decreased and the growth rate was increased with the increase of cooling rate. At the same cooling rate, the grain size with addition of 0.5% TiCNnp was smaller than that with the addition of 0.5% Al-5Ti-1B. The blocking factor f of TiCNnp increases with increasing cooling rate. Based on the free growth model, a new numerical model considering the growth restriction effect of nanoparticles was established. The growth of grain was inhibited by the combining effect of solute and nanoparticles. The growth rate of grain is reduced due to part of the solid/liquid interface coated by nanoparticles. The blocking factor f is linearly decreased with the coverage ratio f which is proportional to the critical grain radius. The grain size decreases with increasing cooling rate and decreasing f . This study is especially beneficial for Al alloys that have poisoning phenomenon inoculated by traditional refiner such as Al-Zr, Al-Si and Al-Sc alloys.

Модель растворения пор на границах зерен при отжиге ультрамелкозернистого алюминиевого сплава

A theoretical model which describes the mechanism of pore dissolution at grain boundaries in ultrafine-grained materials during the ageing annealing is suggested. Within the framework of the model, pore dissolution occurs due to the emission of vacancies and the climb of grain-boundary dislocations along the grain boundary towards the pore. It is shown that in this case there is a significant decrease in the total energy of the system. The results of the model are in good agreement with the available experimental observations of pore dissolution during annealing of ultrafine-grained Al-Zr alloy.

Developing age-hardenable Al-Zr alloy by ultra-severe plastic deformation: Significance of supersaturation, segregation and precipitation on hardening and electrical conductivity

The aluminum-zirconium (Al-Zr) alloys are of interest because of their superior thermal stability and good electrical conuctivity, but their main drawback is their rather low hardness (<75 Hv) even after severe plastic deformation (SPD). These alloys, which are actually composites of Al and Al3Zr intermetallics (D023 tetragonal structure), do not show age-hardening behavior due to the immiscibility of Zr in Al. In this study, ultra-SPD with shear strains up to 40,000, realized by high-pressure torsion (HPT), is employed to generate supersaturated solid solution in an Al-Zr alloy. Subsequent aging leads to unusual precipitation of AlZr precipitates at grain boundaries (Bf orthorhombic structure) and of coherent metastable Al3Zr precipitates within grain interiors (L12 cubic structure). It is found that the supersaturation of Zr in Al by ultra-SPD is controlled by an ultrafast dynamic diffusion which is comparable to surface diffusion, while the formation of precipitates by static aging is controlled by lattice and pipe diffusions. These microstructural features provide exceptional increase in hardness up to 148 Hv, great thermal stability up to 523 K and reasonable electrical conductivity up to 35 %IACS. Detailed analysis shows that ~30% of this hardening is caused by precipitation strengthening, while extra hardening is achieved due to nanograin formation, grain-boundary segregation and dislocation accumulation. This study introduces a rational approach to produce novel age-hardenable Al alloys with high thermal stability and reasonable electrical conductivity by application of ultra-SPD.

The Zr alloying effect on microstructure evolution and mechanical properties of nanostructured Al-Zr alloyed films

Al-Zr nanocrystalline alloy films with Zr contents range from 0 to 8.3 at.% were prepared by magnetron sputtering. The microstructure evolution, mechanical behaviors and strengthening mechanism of films were studied. All the films formed a supersaturated solid solution structure of Zr in the Al lattice. With the increasing of Zr contents, the grain size of films decreased rapidly. When the Zr content increases to 8.3 at.%, the grain size was reduced to about 20 nm. The added Zr atoms tended to segregate at grain boundaries in the Al-Zr alloy films. The hardness of the film gradually increased from 2.5 GPa of pure Al to 5.4 GPa of Al-8.3 at.% Zr film. The strengthening of Al-Zr alloy film comes from three aspects, grain refinement strengthening, solid solution strengthening and nanocrystalline solution pinning strengthening. Among the three strengthening factors of the Al-Zr alloy films, the contribution of fine grain strengthening is the largest, about 70%, followed by solid solution strengthening, 15–20%. The contribution of nanocrystalline solution pinning strengthening is the weakest, less than 10%.

Mechanism of ultrasound-induced microstructure modification in Al–Zr alloys

This work probes the effect of ultrasonic melt treatment (UST) on primary intermetallic particles and α-Al using pure Al and Al–Zr alloys (Al–0.3Zr–0.1Ti, Al–0.5Zr, Al–0.5Zr–0.5Mg–0.9Si) solidified at various cooling rates of 0.2–70 K s−1. The application of UST is shown to decrease the size and increase the number density and volume fraction of D023-structured primary Al3Zr and Al3(Zr,Ti) particles with a high nucleation potency for α-Al formation. High-resolution transmission electron microscopy analysis reveals that the cavitation-induced wetting and dispersion of γ-Al2O3 inoculant particles contribute to the refinement of primary intermetallic particles. The grain size of Al–Zr alloys increases with increasing cooling rate because of the concomitantly reduced formation of primary intermetallic inoculant particles. The UST-induced refinement of primary Al3Zr particles and the increased number density lead to grain refinement in Ti-free Al–Zr alloys. For the Ti-containing Al–Zr alloy, UST-induced grain refinement is achieved only at a very low cooling rate of 0.2 K s−1, possibly because of the side effects of UST on the growth-restricting influence of Ti. The fast cooling–induced solidification enables significant age-hardening by L12-Al3Zr nanoprecipitation (~5 nm) and is not affected by UST. Thus, this study shows that UST can be used to reduce the degree of grain coarsening of age-hardenable Al–Zr alloys at high cooling rates.

Preparation and characterisation of aluminium zirconium oxide for metal‐oxide‐semiconductor capacitor

A functional type metal-oxide-semiconductor (MOS) based capacitor was fabricated and studied by using aluminium zirconium oxide (AlxZryOz) as a potential high dielectric constant (k) gate oxide, which was transformed from as-sputtered Al-Zr alloy after undergoing a wet oxidation at 400°C, 600°C, 800°C, and 1000°C in the presence of nitrogen as a carrier gas. A mixture of tetragonal ZrO2-monoclinic AlxZryOz phases were present at 600°C while stablized tetragonal AlxZryOz phases were detected at higher temperatures with a minute micro strain change. The largest k value (21) was obtained by the film oxidised at 600°C, followed by 800°C while the lowest one at 1000°C. The discrepancy was due to the absence of tetragonal ZrO2 in the latter films. The attainment of a k value closer to the reported value for ZrO2 at 600°C suggested that the tetragonal ZrO2 phase was one of the factors yielding a high k value at 600°C. However, further investigation was required for this sample because the slow trap density and total interface trap density was high despite a high k value, mainly attributed to the presence of negatively charged traps as the scattering centre in the film. The film obtained at 1000°C was not encourageable to be deployed as a passivation layer for Si MOS device due to its low k controlled by the thick interfacial layer.

Corrosion Behaviour Between Al–Zr Alloy Conductor and Cu Transition Terminal via Sc Addition

The influence of Sc microalloying on corrosion behaviour between Al–0.2Zr alloys conductor and Cu sheet have been studied in 0.1 M Na2SO4 + 0.05 M NaCl weak acid solution. The observations of corroded morphologies of the Al–0.2Zr alloys conductor were obtained by scanning electron microscopy and transmission electron microscopy. After same short-term service, slight local corrosion and pitting pits occur on the surface of Al–0.2Zr alloy, and corrosion products mainly adhere along grain boundaries of Al–0.2Zr–0.1Sc alloy. After same long-term service, there are many large and saggy corrosion pits on the surface of Al–0.2Zr–0.1Sc alloy, while only some staircase corrosion marks appear on the surface of Al–0.2Zr alloy. Al3Sc and Al3(Zr,Sc) may reduce the electrochemical heterogeneity and the electrochemical reaction of precipitated precipitates on subgrain boundaries and inter-subgrains, thus improving corrosion resistance via Sc addition.

Vacancy mediated alloying strengthening effects on Al/Al3Zr interface and stabilization of L12-Al3Zr: A first-principles study

The presence of L12-Al3Zr, can drastically improve the strength of Al alloys, however, the L12-Al3Zr is a metastable structure and prone to have phase transformation at the Al/Al3Zr (α/β′) interface. Therefore, it is very important to prevent the phase transformation and stabilize the metastable structure. In this work, the first-principles calculations method based on density functional theory was used to explore the intrinsic mechanism of adding solute atoms to effectively control the phase transition proposed in the experimental research. Based on the determination of the optimal doping sites of atoms, the calculation of the diffusion energy barrier proves that the introduction of alloying elements does hinder the diffusion of atoms, thus effectively suppressing the phase transition process at the interface. From the perspective of Griffith work of fracture (G), the effects of alloying element and vacancy on the interfacial bonding strength were considered. There is the best strength effect while the alloying atom replaces the β′-Al site at the interface with VAl or without VAl, and among the four elements studied, the alloying effect of Nb is the best, and Cu is relatively poor. In addition, the calculation results of the Griffith work of fracture were explained by the electronic local function. The introduction of alloying element makes the change of the degree of electron localization of Al atoms nearby is an important reason for the interfacial bonding strength. The obtained results in the present work instructive for the interfacial strengthening mechanisms and it may serve as a design tool for Al–Zr alloys with desired properties.

Effect of structural order on oxidation kinetics and oxide phase evolution of Al–Zr alloys

To reveal the fundamental role of structural order of the parent alloy on the oxidation mechanism, thermal oxidation of amorphous and crystalline Al–Zr alloys with identical compositions were investigated in detail. An (Al0.68Zr0.32)O1.66 amorphous oxide emerged on crystalline Al2Zr, whereas an (Al0.33Zr0.67)O1.83 amorphous oxide formed on amorphous Al68at.%Zr32at.% under the same conditions. Oxidation kinetics was fast and linear for crystalline Al2Zr but slow and parabolic for amorphous Al68at.%Zr32at.%. The underlying mechanisms of such striking differences were disclosed by molecular dynamics simulations. The findings thus offer new prospects in the field of surface engineering.

Al–Zr alloys synthesis: characterization of suitable multicomponent low-temperature melts

Al–Zr alloys as an advanced metal matrix composite material start to be attractive for various special applications. The electrochemical preparation of aluminium–zirconium alloy from cryolite melts seemed to be very perspective. Characterization of low-temperature sodium and potassium cryolite-based systems with the different additions of ZrO2 and Al2O3 (both as an electrochemical active compounds) was realized. The electrical conductivity of NaF–AlF3–Al2O3–ZrO2 and KF–AlF3–Al2O3–ZrO2 systems as a function of the temperature was studied. The addition of AlF3 varied from 33mol% to 42mol% in the sodium cryolite system and from 40.0mol% to 45.5mol% in the potassium cryolite system. Alumina and/or zirconia were added in amounts up to 1.2mol% and 2mol%, respectively (sodium system), and up to 2.8mol% and 3mol%, respectively (potassium system). The behavior of the electrical conductivity in the studied systems was described by the regression equations valid in a large temperature and concentration ranges.