Al3Zr Phase Research Articles

Precipitation behavior of Al2CuLi, Al3Li and Al3Zr in A2060 aluminum-lithium alloys and mechanical behavior of their microinterfaces

The precipitated phase of Al-Li alloy is a major factor determining the properties of Al-Li alloy. Al2CuLi phase(T1 phase), Al3Li phase and Al3Zr phase are all important enhanced precipitated phases. In this paper, the properties of the matrix, the precipitated phase and the interface formed between each phase are calculated. The (111) crystal face of Al, (111) of Al3Li, (111) of Al3Zr, and (210) of Al2CuLi are the surfaces with the lowest surface energy of these phases. Al3Li/Al3Zr has the lowest interfacial energy (0.01961ev), so its thermodynamic stability is the best. The interface with the maximum bonding strength is the interface of Al3Zr/T1, and its adhesion work is 0.61878ev. A2060 aluminum-lithium alloy was thermally insulated at 580 °C for 2h and then hot rolled. After hot rolling, it was cooled to room temperature for cold rolling. Then the samples were treated with solid solution and aging, and different cooling methods were selected to obtain four kinds of samples: non-heat treatment, aging, air cooling and water quenching. It is found that the strength and hardness of Al-Li alloy are determined by the grain thickness of precipitated phase, and the ductility and hardness of Al-Li alloy are determined by the number of precipitated phase and the degree of dislocation density.

Enhancing the dehydrogenation properties of LiAlH4 through the addition of ZrF4 for solid-state hydrogen storage

Hydrogen energy is emerging as an essential alternative to fossil fuels due to its clean energy profile, generating energy without greenhouse gas emissions. Solid-state hydrogen storage, particularly using complex hydrides like LiAlH4, holds promise due to high hydrogen capacities. However, practical applications of LiAlH4 face obstacles due to slow dehydrogenation kinetics and high decomposition temperatures. This study investigates the catalytic effect of ZrF4 on LiAlH4 to improve hydrogen storage properties. Incorporating 10wt.% ZrF4 has significantly lowered the onset desorption temperature from 160 °C to 80 °C. Desoption kinetic result showed that the addition of 10wt.% ZrF4 can enables the release of 5.6wt.% hydrogen in 120min at 100 °C, which is 50 times faster than in undoped samples. X-ray diffraction analysis indicated that ZrF4 facilitated the in-situ formation of Al3Zr and LiF phases during dehydrogenation, thereby enhancing catalytic efficiency. The desorption activation energies for first two reactions decreased significantly by ~ 16kJ/mol and ~24kJ/mol with ZrF4 doping. These findings suggest that ZrF4 effectively improves the hydrogen storage properties of LiAlH4, positioning it as a potential catalyst for solid-state hydrogen storage systems.

Investigation of nanoscale strain fields induced by the L12–Al3Zr phase in Al–Zn–Mg–Cu alloys

Al–Zn–Mg–Cu alloys are widely used in aerospace as an advanced lightweight structural material. The precipitation of the nanoscale L12–Al3Zr phase enhances the mechanical properties of the alloy. This study employs scanning transmission electron microscopy and geometric phase analysis techniques to investigate the strain fields induced by the nanoscale L12–Al3Zr phase. The findings demonstrate that after the precipitation of the L12–Al3Zr phase, the strain within the L12–Al3Zr phase is negligible, and a coherent strain field is developed near the L12–Al3Zr/Al interface. Characterizing the coherent strain fields of the nanoscale L12–Al3Zr phase provides a valuable reference for optimizing the mechanical properties of Al alloys.

EVOLUTION OF THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF AL-B COMPOSITE WITH THE ULTRAFINE-GRAINED ALUMINUM MATRIX

The paper examines the microstructural evolution of alloy 1565ch of the Al-Mg-Mn-Zn-Zr system during thermomechanical treatment, including severe plastic deformation by high-pressure torsion or equal channel angular pressing according to the conform scheme and subsequent isothermal rolling at 200°C. Formation of the nanostructured and ultrafine-grained states in alloy 1565ch with the controlled distribution of Al3Mg2, Al6Mn and Al3Zr phases both inside grains and at their boundaries allows for the superplastic effect at the temperatures 250 and 300°C and strain rates 5 × 10-2, 10-2, and 5 × 10-3 s-1. Microstructural analysis by transmission electron microscopy shows that superplastic deformation at the temperatures 250 and 300°C allows a homogeneous ultrafine-grained state to be preserved. The studied ultrafine-grained aluminum alloy 1565ch has a high strength and the ability to relieve stresses, and therefore it can be favorably used as the matrix material in composites reinforced with continuous boron fibers. In the paper, we use this alloy to study special features of production of a multilayer metal matrix composite according to the foil-fiber-foil scheme by isothermal pressing in the low-temperature superplastic mode. This method has a positive effect on the mechanical properties of the composite, such as ultimate strength at 200°C, impact strength at room temperature, and fracture toughness at room temperature.

“Branched” structural transformation of the L12-Al3Zr phase manipulated by Cu substitution/segregation in the Al-Cu-Zr alloy system

The effect of Cu on the evolution of the Al3Zr phase in an Al-Cu-Zr cast alloy during solution treatment at 500 °C has been thoroughly studied by combining atomic resolution high-angle annular dark-field scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy and first-principles calculations. The heat treatment initially produces a pure L12-Al3Zr microstructure, allowing for about 13 % Cu to be incorporated in the dispersoid. Cu incorporation increases the energy barrier for anti-phase boundary (APB) activation, thus stabilizing the L12 structure. Additional heating leads to a Cu-induced “branched” path for the L12 structural transformation, with the latter process accelerated once the first APB has been created. Cu atoms may either (i) be repelled by the APBs, promoting the transformation to a Cu-poor D023 phase, or (ii) they may segregate at one Al-Zr layer adjacent to the APB, promoting a transformation to a new thermodynamically favored phase, Al4CuZr, formed when these segregation layers are periodically arranged. Theoretical studies suggest that the branching of the L12 transformation path is linked to the speed at which an APB is created, with Cu attraction triggered by a comparatively slow process. This unexpected transformation behavior of the L12-Al3Zr phase opens a new path to understanding, and potentially regulating the Al3Zr dispersoid evolution for high temperature applications.

Precipitation hardening and structure evolution in hypereutectic Al-6 % Fe-Zr alloys subjected to ultrasonic melt processing

The objective of this research was to study the influence of Zr concentration and ultrasonic melt processing (USP) on the microstructure and precipitation hardening of a hypereutectic Al-6% Fe alloy. Such alloys have a good potential in high-temperature, wear-resistant, and conducting applications but suffer from coarse structure and low strength/ductility, which prevents their processing. The microstructure of the studied alloys consisted of primary Al13Fe4 intermetallics and (Al)+Al13Fe4 eutectic colonies, which were successfully refined by adding Zr and performing USP. The mechanisms of USP and Zr were confirmed for the Al-6 % Fe alloys with a range of Zr additions. The structure refinement led to improved hardness and tensile properties of the alloys. All studied alloys demonstrated strong precipitation hardening effect with hardness increasing 4–5 times, reaching 170 HV for the alloy with 0.4 % Zr after annealing at 400 ℃ for 20 hrs. The electrical conductivity increased from 25 % IACS in the as-cast alloy to 40% IACS in the annealed Al-6% Fe-0.4 % Zr alloy. The prime novelty of this work is a considerable increase of hardness upon annealing, i.e. more than 100 HV, in the Al-6 % Fe alloy with only minute traces of Zr (<0.01 %). The precipitation phenomena were investigated by transmission electron microscopy. The precipitation of the semi-coherent Al13Fe4 phase with Zr segregated to its surface was observed for the first time. All studied alloys (with minute and larger Zr additions) showed the precipitation of this phase, while the alloys with the larger amount of Zr also demonstrated the precipitation of the metastable L12 Al3Zr phase. Therefore, the properties improvement was attributed to the structure refinement and the formation of Zr-modified Al13Fe4 and Al3Zr precipitates in the microstructure.

Dynamic precipitation and its effect on microstructure of 2195 Al–Li alloy during medium/high temperature deformation

In this work, the homogenized Al–Li alloys were compressed at different strains (20%–80%) under medium (370 °C) and high temperatures (470 °C), and their microstructures were characterized by SEM, EBSD, and TEM. The evolution of dynamic precipitation (DPN) during thermal deformation and its effect on microstructure and flow behavior were investigated. The results show that obvious flow softening appears with the increase of strain at medium temperature deformation while not at high temperatures, associated with the reduction of solid solution strengthening caused by DPN and the fragmentation of T1 precipitates with large aspect ratios. The T1 precipitates undergo fragmentation, dissolution and re-precipitation to develop two types of T1 bands. Deformation at medium temperatures, DPN inhibits dislocations and (sub)grain boundary movement, and mainly dynamic recovery (DRV) accompanied by little dynamic recrystallization (DRX) occurs. The fine secondary phases at high temperatures are dominated by the pre-existing Al3Zr phase, and some precipitates are observed until 80% strain, however, DPN has little influence on precipitation hardening and DRX and occurs later than DRX. DRX mechanism changes from CDRX (20–60%) to CDRX and GDRX (80%) with strain at high temperatures. Furthermore, the deformed grains tend to develop in <101>//CD (compression direction) fiber texture during deformation, and the texture strength increases with increasing strain and decreasing temperature.

The Influence of Homogenisation Parameters on the Microstructure and Hardness of AlMnFeMgSi(Zr) Wrought Alloys

The purpose of this investigation is to improve the mechanical properties of AlMnFeMgSi wrought alloys by forming a high number density of nano-scaled strengthening dispersoids during homogenisation annealing. The process chain for AlMnFeMgSi wrought alloys includes homogenisation annealing after continuous casting. In this step, inhomogeneities and segregations are dissolved and dispersoids are precipitated. The formed dispersoids hinder grain growth, but usually cannot increase the strength due to their coarse size of some 100 nm. Lower homogenisation temperatures should result in the precipitation of smaller dispersoids during homogenisation. The addition of Zr was investigated to increase this effect. Zr should form further dispersoids from the Al3Zr phase. This requires a fundamental understanding of the temperature-dependent kinetics and the nature of precipitation formation during homogenisation. For this purpose, the as-cast state is first characterised via differential scanning calorimetry. Subsequently, a large number of homogenisation parameters are investigated and quantified via hardness testing. The micro- and nanostructure are investigated for promising parameters and a particle analysis is performed. In the present study, it was possible to precipitate fine dispersoids of few 10 nm by reducing the homogenisation temperature, which resulted in a significant increase in hardness. Alloying with Zr enabled the precipitation of further dispersoids with a size of a few nm in a high number density, which further increased the strength.

First-Principles Study of Atomic Diffusion by Vacancy Defect of the L12-Al3M (M = Sc, Zr, Er, Y) Phase.

Atomic diffusion by the vacancy defect of L12-Al3M (M = Sc, Zr, Er, Y) was investigated based on a first-principles calculation. The point defect formation energies were firstly evaluated. Then, the migration energy for different diffusion paths was obtained by the climbing-image nudged elastic band (CI-NEB) method. The results showed that Al atomic and M atomic diffusions through nearest-neighbor jump (NNJ) mediated by Al vacancy (VAl) were, respectively, the preferred diffusion paths in Al3M phases under both Al-rich and M-rich conditions. The other mechanisms, such as six-jump cycle (6JC) and next-nearest-neighbor jump (NNNJ), were energetically inhibited. The order of activation barriers for NNJ(Al-VAl) was Al3Zr < Al3Y < Al3Er < Al3Sc. The Al3Sc phase had high stability with a high self-diffusion activation barrier, while the Al3Zr and Al3Y phases were relatively unstable with a low self-diffusion activation energy. Moreover, the atomic-diffusion behavior between the core and shell layers of L12-Al3M was also further investigated. Zr atoms were prone to diffusion into the Al3Y core layer, resulting in no stable core-shelled Al3(Y,Zr), which well agreed with experimental observation.

Microstructure, mechanical properties, and damping capacity of high-Zn-content Al–Zn–Mg alloys with Sc and Zr additions

In this study, Al–15Zn–0.5 Mg–Sc–Zr alloys with different Sc and Zr contents were fabricated by casting, rolling, solution treatment, and aging at low and high temperatures. Primary and precipitated Al3(Sc,Zr) and Al3Zr phases could promote grain refinement in the high-Zn-content Al alloys more effectively than the Al3Sc phase, and the composition characteristics of high Zn and low Mg contents led to the Al–15Zn–0.5 Mg–Sc–Zr alloys exhibiting high thermal stability of η′ phases during aging at high temperature and long time. The Al3Sc and Al3(Sc,Zr) phases could promote the formation of fine η phases in the Al–15Zn–0.5 Mg–Sc–Zr alloys, but the Al3Zr phase could not. Finer grains and second phases led to the Al–15Zn–0.5 Mg–Sc–Zr alloys with Zr single addition and Sc, Zr collaborative additions exhibiting better mechanical properties than the alloy with Sc single addition. Meanwhile, the damping capacities of the Al–15Zn–0.5 Mg–Sc–Zr alloys with high-temperature aging were higher than those of the same alloys with aging at a low temperature due to their less numbers of dislocation pinning points and higher interface slipping ability.

Nucleation of L12-Al3M (M = Sc, Er, Y, Zr) Nanophases in Aluminum Alloys: A First-Principles ThermodynamicsStudy

High-performance Sc-containing aluminum alloys are limited in their industrial application due to the high cost of Sc elements. Er, Zr, and Y elements are candidates for replacing Sc elements. Combined with the first-principles thermodynamic calculation and the classical nucleation theory, the nucleation of L12-Al3M (M = Sc, Er, Y, Zr) nanophases in dilutealuminum alloys were investigated to reveal their structural stability. The calculated results showed that the critical radius and nucleation energy of the L12-Al3M phases were as follows: Al3Er &gt; Al3Y &gt; Al3Sc &gt; Al3Zr. The Al3Zr phase was the easiest to nucleate in thermodynamics, while the nucleation of the Al3Y and Al3Er phases were relatively difficult in thermodynamics. Various structures of Al3(Y, Zr) phases with the radius r &lt; 1 nm can coexist in Al-Y-Zr alloys. At a precipitate’s radius of 1–10 nanometers, the core–shelled Al3Zr(Y) phase illustrated the highest nucleation energy, while the separated structure Al3Zr/Al3Y obtained the lowest one, and had thermodynamic advantages in the nucleation process. Moreover, the core–shelled Al3Zr(Y) phase obtained a higher nucleation energy than Al3Zr(Sc) and Al3Zr(Er). Core–doubleshelled Al3Zr/Er(Y) obtained a lower nucleation energy than that of Al3Zr(Y) due to the negative ΔGchem of Al3Er and the negative Al3Er/Al3Y interfacial energy, and was preferentially precipitated in thermodynamics stability.

Study on the Effect of Microstructures and Properties of Al-Mg-Mn-Zr Alloy Welding Wire by Adding Minor Sc

The low strength of welded joints of aluminum alloy welding wire materials has seriously restricted the promotion and application of high-performance aluminum alloys represented by 7A52 and 7B52 aluminum alloy. It is urgent to develop new high-strength aluminum alloy welding wire material to meet the lightweight application demand of 7××× series high-performance aluminum alloy materials in military and civilian vehicles. This paper studied the effect on microstructures, mechanical properties, and welding properties of Al-6Mg-0.3Mn-0.2Zr welding wire alloys by adding minor Sc elements. The result shows that it formed Al3Zr, Al3Sc, and Al3(Sc1-x, Zrx) primary dispersive phases in the matrix, and the Al3(Sc1-x, Zrx) primary phase, which had triple-shell microstructure composed of Al3Zr/α(Al)/Al3Sc three-layer phases enclosing individually with each other from the center to outside. These phases could promote heterogeneous nucleation during solidification and crystallization in the process of welding, resulting in strong refinement and strengthening effects in the weld-zone microstructure. The welding joint mechanical properties of both tensile strength and elongation increased with the increase of Sc contents within the range of 0–0.4%. It was reached at Rm 365 MPa/A 5% without means of heat treatment which are much higher than aluminum alloy welding wires used in current engineering when the 7B52 aluminum alloy laminated plates were welded with the prepared welding wire Al-6Mg-0.3Mn-0.2Zr alloys of 0.385% Sc.

The Effects of Double-Step Homogenization on Precipitation Behavior of Al3Zr Dispersoids and Microstructural Evolution in 2196 Aluminum Alloy

The effects of double-step homogenization processes on the precipitation of Al3Zr dispersoids and the dissolution of the primary phases of 2196 aluminum alloy were studied by optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was revealed that first-step homogenization facilitates the nucleation of Al3Zr, while second-step homogenization results in the dissolution of the primary phases and the growth of Al3Zr dispersoids. The nanosized θ’ precipitates formed in the first-step homogenization are dissolved after the second-step homogenization. The optimum homogenization process was selected as 400 °C/10 h + 520 °C/24 h, which effectively dissolves the primary phases and promotes the formation of refined distribution of Al3Zr dispersoids. This phenomenon is mainly caused by the highest nucleation rate of the Al3Zr phase at 400 °C. While reducing the heating rate of the homogenization process can increase the number density of the Al3Zr dispersoids and reduce the precipitate free zone (PFZ), it does not alleviate the inhomogeneity of the Al3Zr precipitation. These results are expected to be meaningful for tailoring the industrial homogenization processing of as-cast Al-Cu-Li alloy.

Prediction of heat-resistant Al–Fe–Cu–Zr alloy from first-principles calculations: Stoichiometries, electronic structure, and physical properties

To investigate the effect of Zr on the properties of the Al–Fe–Cu system, the structural stability, electronic structure, and thermodynamic properties of the Al3Zr, Al6Fe, Al2Cu, and Al7FeCu2 phases were calculated and analyzed using the plane wave pseudo-potential method based on the first principles calculation. The results show that the addition of Zr can improve the thermal stability and melting point of aluminum alloy cables, but has a limit on the mechanical properties. Compared with Al6Fe, Al2Cu, and Al7FeCu2, Al3Zr exhibits better alloying ability and structural stability at 0 K. By comparing the density of states (DOS) and the number of transferred electrons, it is found that the Al3Zr phase has strong covalent bond characteristics. The elastic constants of Al3Zr, Al6Fe, Al2Cu, and Al7FeCu2 are calculated. It is found that the anisotropy of Al3Zr and Al7FeCu2 is small, and the mechanical properties of Al6Fe and Al2Cu are brittle, while the mechanical properties of Al6Fe and Al2Cu are plastic. According to the empirical formula, Al3Zr has the highest microhardness and melting point. In addition, it is found that the Al3Zr phase has the best thermal stability by thermodynamic analysis. The good thermal stability of Al3Zr was verified. In conclusion, this paper provides a theoretical basis for the thermodynamic optimization of the heat-resistant alloy Al–Fe–Cu–Zr series.

Effect of Cooling Rate and Remelting Temperature on the Solidification Structure of Al-5Zr Master Alloy

Zr is an important element to improve the heat resistance of aluminum alloys, which is usually added to alloys using the Al-Zr master alloys. The microstructure of Al-Zr master alloys has a significant impact on the properties of Zr-bearing aluminum alloys. In this paper, the microstructure of commercial Al-5Zr master alloys was examined, and the effect of the remelting temperature and cooling rate on the solidification structure of the remelted Al-5Zr master alloys was investigated, aiming to develop a feasible way for quality improvement of Al-5Zr master alloys. The results showed that the microstructure of the remelted Al-5Zr master alloy could be regulated effectively by controlling the remelting temperature and cooling rate. When the remelting temperature was 1320 °C, the primary Al3Zr phase in the remelted Al-5Zr master alloy was mainly precipitated as coarse plate-like or fine long needle-like. Higher cooling rate increased nucleation density and refined microstructure. The average length of the primary Al3Zr phase was 178.2, 87.4, and 61.3 μm when the cooling rate was 4.6, 30.8, and 43.9 °C/s, respectively. Lower remelting temperature was generally conducive to refinement of primary Al3Zr phase. When the remelting temperature was 920 °C, the primary Al3Zr phase in the remelted Al-5Zr master alloy was mainly precipitated as block-like, fine needle-like, and petal-like. When the cooling rate was 4.6 °C, coarse plate-like Al3Zr phase precipitated. With increasing cooling rate to 25.3 °C, the coarse plate-like Al3Zr phase disappeared and the block-like and fine needle-like Al3Zr phase precipitated followed by a large number of fine petal-like Al3Zr phase precipitated after cooling rate to 45.6 °C. The optimized remelting process can improve the microstructure of the commercial Al-5Zr master alloy.

Effect of Cr on the Microstructure and Mechanical Properties of the Al-Cu-Y-Zr Alloy

The present investigation aimed at the determination of Cr addition on microstructure, phase composition, and mechanical properties of the Al-Cu-Y-Zr alloy. Quasi-binary alloys of the ternary Al-Cu-Y system with atomic rotation of Cu/Y = 4/1 have a narrow solidification range with high solidus temperature. The addition of 0.3% Cr in the Al-5.1Cu-1.7Y-0.3Zr alloy provides a formation of a novel quaternary Al81–85Cu7–10Y3–4Cr5 phase. L12-Al3(Zr,Y) phase spherical particles with a diameter of 50 nm were nucleated during solution treatment at 600 °C. Al7Cr precipitates were not found in the microstructure. The main strengthening effect of 32.4 MPa and 29.1 MPa was achieved from L12 and θ’(Al2Cu) precipitates, respectively, in accordance with the calculation. The calculated hardness of 61.5HV based on the calculated σy is consistent with the experimental value of hardness. Al3Zr and Al7Cr phases should be in equilibrium with (Al) in accordance with the calculated polythermal section. However, transmission electron microscopy investigation demonstrates the Al3(Zr,Y) precipitates only. As a result, the dissolved Cr atom provides a slightly higher hardness in the rolled and annealed AlCuYZrCr alloy. A suitable combination of strength and ductility was observed both after rolling and after rolling with subsequent annealing at 150 °C for 3 h—the alloy exhibited a yield strength of 308–315 MPa, an ultimate tensile strength of 323–335 MPa, and an elongation to failure of 2.0–3.3%.

Theoretical Prediction of Structural, Mechanical, and Thermophysical Properties of the Precipitates in 2xxx Series Aluminum Alloy

We presented a theoretical study for the structural, mechanical, and thermophysical properties of the precipitates in 2xxx series aluminum alloy by applying the widely used density functional theory of Perdew-Burke-Ernzerhof (PBE). The results indicated that the most thermodynamically stable structure refers to the Al3Zr phase in regardless of its different polymorphs, while the formation enthalpy of Al5Cu2Mg8Si6 is only -0.02 eV (close to zero) indicating its metastable nature. The universal anisotropy index of AU follows the trend of: Al2Cu &gt; Al2CuMg ≈ Al3Zr_D022 ≈ Al20Cu2Mn3 &gt; Al3Fe ≈ Al6Mn &gt; Al3Zr_D023 ≈ Al3Zr_L12 &gt; Al7Cu2Fe &gt; Al3Fe2Si. The thermal expansion coefficients (TECs) were calculated based on Quasi harmonic approximation (QHA); Al2CuMg shows the highest linear thermal expansion coefficient (LTEC), followed by Al3Fe, Al2Cu, Al3Zr_L12 and others, while Al3Zr_D022 is the lowest one. The calculated data of three Al3Zr polymorphs follow the order of L12 &gt; D023 &gt; D022, all of them show much lower LTEC than Al substance. For multi-phase aluminum alloys, when the expansion coefficient of the precipitates is quite different from the matrix, it may cause a relatively large internal stress, or even produce cracks under actual service conditions. Therefore, it is necessary to discuss the heat misfit degree during the material design. The discrepancy between a-Al and Al2CuMg is the smallest, which may decrease the heat misfit degree between them and improve the thermal shock resistant behaviors.

Effect of Aging Treatment on the Precipitation Behavior of a Novel Al-Cu-Zr Cast Alloy.

A novel Al-Cu-Zr alloy is designed in this paper, which provides a method for further improving the strength of Al-Cu alloys. In this paper, the addition of the micro-alloying element Zr in Al-Cu alloy was studied. The effect of aging treatment on the mechanical properties and precipitation behavior of the alloy was studied. With the addition of Zr, Al3Zr phases were formed in the alloy, which acts as obstacles to dislocation motion. In addition, Al3Zr phases can be used as the nucleation site of θ' phases to promote precipitation. All this can improve the strength of Al-Cu alloys. After one-step aging, corresponding to the highest hardness, the largest amount of θ' phases were observed in the alloy matrix. By contrast, after two-step aging, the θ' phases were finer, and a large amount of Guinier-Preston (GP) zones formed during the pre-aging step, which were transformed into denser and finer θ' phases in the secondary aging step. After the same solution treatment (540 °C/12 h), undergoing 120 °C/4 h + 175 °C/10 h two-step aging, the ultimate tensile strength, yield strength, and elongation of the Al-Cu-Zr alloy were 398.7 MPa, 313.3 MPa, and 7.9%, respectively.

True Stress-Strain Behavior of Al-based Cast Automotive Alloy Under Different Ageing Conditions and the Effect of Trace Zr

A thorough investigation has been carried out on the Al-12Si-1Mg-1Cu-1Ni automotive alloy considering different properties, specially mechanical properties associated with true stress and true strain with Zr addition of trace amount. A commercially available piston is melted to produce the alloy, and trace amount of Zr is added to make another. The base alloy along with the Zr added alloy had been applied to homogenization, solution treatment, quenching, and ageing in order to get the age-hardening response. The alloys have been heat-treated at 25 ºC, 200 ºC, and 300 ºC, respectively, for four hours for attaining the under, peak and over-aged states, respectively. During ageing, Al2Cu and Mg2Si phases are formed in the aluminium matrix leading to peak-aged strength, which is reduced at over-aged state because of coarsening of precipitation and recrystallizing, shown by the tensile and hardness properties. When Zr is added to the alloy, Al3Zr phases appear while casting and heat-treatment, resisting the drop of strength at over-aged state. It is visible in the stress-strain diagram that at over-aged conditions, the alloy with trace Zr shows improved strength and ductility. In the micrographs of Zr added alloy, finer distributed grains are visible through the grain refinement of Zr, which also prevents recrystallization at over-aged conditions. The homogeneity of the grains as a result of the Zr addition's microstructural change was further confirmed by fractography. It is clear that adding Zr to such alloys does not greatly increase their strength, but it does restrict the declining of strength by preventing the production of thermally stable Al3Zr precipitates, which coarsens the resisting behavior of various intermetallics in the thermally damaged alloy.

The Effect of Thermomechanical Processing Sequence on the Dispersoid Distribution and Final Mechanical Properties of Spray-Formed Al-Cu-Li Alloy

Controlling the formation of the β′ (Al3Zr) phase is pivotal for regulating the recrystallization and thus the mechanical properties of the spray formed 2195 (Al-Cu-Li) alloy. In a conventional “homogenization-extrusion” process, the precipitation of β′ is severely affected by the presence of the T1(Al2CuLi) phase in the as-deposited alloy, leading to an inhomogeneous distribution of the β′ phase. In the present work, we propose a new thermomechanical processing (TMP)—swapping the order of the homogenization and extrusion processes. The microstructures and properties of the new proposed TMP were systematically studied at various stages of the alloy treatment and compared with the out of the conventional TMP. It was revealed that the introduction of the extrusion process on the as-deposited alloy can break the continuous network of primary phases and dissolve the T1 phase, promoting a uniform distribution of the β′ phase during subsequent two-step homogenization. During solution treatment, the new TMP is more effectively in suppressing the formation of a coarse grain layer at sheet surface, while after final peak aging, the new TMP produces a lower alloy strength but a higher elongation, due mainly to the smaller thickness reduction during deformation. The new proposed TMP technique provides a new insight into regulating the mechanical properties of Al-Cu-Li alloys.