High Performance Aluminum Alloys Research Articles

Relationship between cooling rate, microstructure evolution, and performance improvement of an Al–Cu alloy prepared using different methods

The relationship between the cooling rate and microstructure evolution and the performance improvement of an Al–4.5 wt% Cu alloy prepared using different casting methods was investigated. The microstructure evolution, solute element distribution, and mechanical properties of specimens prepared using different cooling rates were systematically investigated using multi-scale optical microscopy, scanning electron microscopy, transmission electron microscopy, tensile testing, and hardness testing. Upon increasing the cooling rate from 1.65 to 117.3 K s−1, the average grain size, secondary dendrite arm spacing, and width and area fraction of eutectic phases significantly decreased, and the density of the precipitated phase, super-saturation degree of solute elements, and mechanical properties improved. Through a combination of grain-boundary, solid-solution, and precipitation strengthening, the cooling rate indirectly affected the mechanical properties of the heat-treated alloy sheets. The Al−4.5 wt% Cu alloy prepared by twin-roll casting under a cooling rate of 117.3 K s−1 exhibited a strength between 145.33 and 321.79 MPa and an elongation of 11.65%, demonstrating its potential as a high-performance aluminium alloy.

Precipitation hardening and intergranular corrosion behavior of novel Al–Mg–Zn(-Cu) alloys

High-performance aluminum alloys are desired for applications that require lightweight materials, but it is challenging to overcome the tradeoff between their strength and intergranular corrosion resistance. To overcome this tradeoff, we have prepared novel Al–Mg–Zn (-Cu) alloys with highly Zn content combined with Cu addition. The alloys with a (Zn + Cu)/Mg ratio below 1.5 are different from traditional 2000, 5000 and 7000 series aluminium alloys. The results show that the number density and lattice spacing of intragranular precipitates increase, while the precipitate sizes decreases with the increase of (Zn + Cu)/Mg ratio, which is the reason for the increase of the alloy strength. Meanwhile, the intergranular corrosion resistance of the alloys is also enhanced by decreasing the potential between grain boundary precipitates and the Al matrix, especially in alloys with high (Zn + Cu)/Mg ratios. These results provide a new method for obtaining high-strength and corrosion-resistant aluminum alloys.

Zn/Cu regulated critical strain and serrated flow behavior in Al–Mg alloys

Next-generation high performance aluminum alloys are required for lightweight strategies and advanced automotive applications. A current challenge for 5xxx series alloys is their poor strength and dreadful surface appearance caused by serrated yielding behavior during plastic deformation. Here we show that the serrated yielding behavior can be eliminated in Zn/Cu modified novel alloys, while simultaneously achieving above 100 MPa improvement of the strength at a pre-aging temper. The formation of GP zones of the precursor of T-Mg32(AlZnCu)49 phase during pre-aging treatment and the depletion of vacancies are mainly attributed to the elimination of dynamic strain aging. The critical strain shows a transformation from normal to inverse behavior with an increase of Zn content in the high-strength novel alloys. Such inverse behavior is because of the impediment of GP zones and solute atoms to the dislocations at lower strain rates. These results provide insight into the serrated yielding behavior of the aluminum alloys.

Investigation on precision warm hydroforming with independent circumferential pressure of high-performance aluminum alloy parts with special-shaped bottom

High-performance aluminum alloy is light, has high strength, but is very difficult to be formed. In the forming process of aluminum alloy parts with special-shaped bottom, there are defects such as poor fittability accuracy, instability, and cracking at the complex bottom, and the forming accuracy is an important performance index to characterize the forming quality. In this paper, a precision warm hydroforming scheme of pre-bulging and deep drawing is designed, and a method of applying independent circumferential pressure on the periphery of the flange in the later stage of pre-bulging is proposed to maintain the shape of the bottom and improve the fittability accuracy. The effects of temperature difference and independent circumferential pressure on the wall thickness and fittability of the part are studied. At the same time, response surface method is used to study the interaction among pre-bulging pressure, liquid chamber pressure, and circumferential pressure, and the optimal forming conditions are obtained after optimization and compared with the test piece. The results show that independent circumferential pressure can significantly improve the ability of the bottom of the pre-bulged part to maintain the acquired shape, and the temperature difference can effectively improve the plasticity of the sheet, the depth of drawing, and the quality of the part. After optimization by response surface method, the minimum wall thickness of the part is 0.8013 mm and the fittability is 94.2%. The forming quality parameters of the test piece are in good agreement with the numerical simulation parts, which indicates that this simulation can effectively predict forming situation of the part, and provides scientific guidance for precision forming of complex-shaped bottom parts.

Effect of Heterogeneous Lamellar Structure on Mechanical Properties and Electrochemical Corrosion Behavior of Al-Zn-Mg-Cu Alloy Subjected to High-Pressure Torsion

The heterogeneous lamellar structure composed of a mixture of coarse crystal layer and fine crystal layer can improve the mechanical properties and corrosion resistance of the metal. To obtain high-performance aluminum alloy with heterogeneous lamellar structure, high-pressure torsion experiments have been carried out at 360, 380 and 400 °C. The results of tensile test and electrochemical corrosion test show that the strength of the alloy increases from 682.46 to 781.03 MPa and the polarization resistance increases from 42.91 to 81.12 kΩ cm2 with the increase in deformation temperature. It can be inferred from optical microscopy and transmission electron microscope observations that the strength of the alloy increases with increasing temperature. This is because the geometrically necessary dislocations at the interface increase during the stretching process, which in turn increases the back stress. Moreover, the enhancement of chemical corrosion resistance can be attributed to the decreased volume fraction of grain boundaries, which results in an increase in the compactness of the passivation film in the corrosive environment.

Anisotropic behavior of TiB2 nanoparticles reinforced 2024Al composites rolling sheet

The in-plane anisotropy (IPA) of mechanical properties existed in plate products is often undesired since it limits the industrial application and increases the difficulty of material processing. It is thus one of the important factors which requires strict control during the manufacture of high-performance aluminum alloy plates. The anisotropic behavior of TiB2/2024Al composite rolling sheet under different heat treatment is studied in this article. T4 heat treated specimen shows good isotropy of yield strength and its texture components are significantly weakened compared with traditional Al alloys. The evolution of microstructures for T4 specimen was studied. The submicron TiB2 particles increase the driving force of recrystallization during rolling process and static recrystallization (SRX) is stimulated, thus induces texture randomization. Anisotropic behavior of yield strength occurs in specimen after T3 heat treatment. It is supposed that the difference in the activation of slip system under different loading direction gives rise to this anisotropy.

Research on Residual Stress Simulation on High Performance Aluminum Alloy Manufacturing

High-performance manufacturing is an integrated manufacturing of surface integrity and anti-fatigue surface strengthening to improve the service performance of key components. The stress concentration, fatigue failure and poor reliability cause by traditional processing have become technical bottlenecks restricting the development of industry. In order to research the influence of high performance manufacturing on the fatigue performance of workpieces, the residual stress distribution of 7050 aluminum alloy high performance manufacturing was studied by simulation. The stress layer on the surface of the workpiece was mainly tensile stress which was formed during cutting process, and it implied that the fatigue resistance of the workpiece was not effectively improved. The ultrasonic rolling strengthening treatment can effectively eliminate the residual tool marks and stress concentration. It was noted that stress layer of ultrasonic rolling was deeper than the cutting process, and the stress layer was mainly composed of residual compressive stress. The residual stress increased first and then decreased with the increased of depth, which can significantly improve the fatigue performance and service life of the workpiece.

Solid-state additive manufacturing high performance aluminum alloy 6061 enabled by an in-situ micro-forging assisted cold spray

Cold spraying is a competitive additive manufacturing method featuring several unique characteristics and allows large-scale production of metallic components from a wide range of materials. In literature, high performance cold sprayed aluminum deposits produced using high-cost helium gas have been qualified for various applications. In this study, high performance aluminum alloy 6061 (AA6061) deposits were produced through a cold spray method using low-cost nitrogen gas enabled by an in-situ micro-forging effect (MF-CS). Results show that the MF-CS AA6061 deposit presents very low porosity as well as high ultimate tensile strength (UTS) and elastic modulus (E). Moreover, the MF-CS AA6061 deposit consists of superior equiaxed submicron fine Al grains with random orientations. However, the severe work hardening induced by intensive particle plastic deformation during deposition leads to very low ductility of the MF-CS AA6061 deposit. To eliminate this limitation, three strategies of heat treatments (stress relieving, recrystallization annealing and T6) were performed to the MF-CS AA6061 deposit. It was found that heat treatment generated complex effects on both inter-particle bonding and inner-particle microstructure (grain size, dislocation density and precipitation) and different strategies lead to different mechanical properties of AA6061 deposits. Among them, T6 heat-treated AA6061 deposits give the best overall mechanical properties with comparable UTS and E and only slightly inferior ductility to the corresponding T6 bulk.

Development of Aluminum Alloy Materials: Current Status, Trend, and Prospects

This study comprehensively analyzes the application status of aluminum alloy materials in aerospace, transportation, and other fields, and introduces the industry scale and technical level of the aluminum alloy materials in China. Moreover, the main problems of this industry are systematically summarized in view of the shortcomings of some key aluminum alloy materials in China as well as the deficiencies in original technologies such as high-performance aluminum alloy development, processing technology, and intelligent control. And the market demand for the aluminum alloy materials is analyzed based on the development trend of automobile, ship, aerospace, and other fields. According to the current status of the aluminum alloy industry in China, the following countermeasures and suggestions are proposed: enhancing the research and development system to improve the development environment; optimizing the production structure to promote production quality and efficiency and coordinate the development; strengthening policy support; promoting talent team construction; promoting intelligent manufacturing and the Internet Plus initiative; and strengthening international cooperation, particularly along the Belt and Road. This study is expected to help solve some critical problems of the industry and provide a reference for promoting the advanced and green development of aluminum alloy materials.

Experimental and simulation study for rewelding defects during the flow process of Semi-solid die casting

Semi-solid die casting process due to its advantages of compact process, high performance and low cost is widely applied in automobile, communication and other industries for the preparation with high performance aluminum alloy castings. Compared with liquid metal melt, the filling behavior is laminar flow for semi-solid metal melt with higher apparent viscosity. In the process of semi-solid die casting, the semi-solid metal melt from different directions came together, it will lead to “rewelding” defects if with insufficient fusion or uneven slurry state. In this paper, the formation reasons and forms of flow “rewelding” defects are analyzed. By numerical simulation and experimental analysis, the flow state of semi-solid metal melt at the junction of filling frontier is represented, and the state of “rewelding” defect is characterized. The effect of eliminating defects is analyzed by modifying the mold structure, such as redesigning overflow and venting systems at the confluence position. The results show that the microstructure of the “rewelding” defects in the confluence position of the semi-solid metal melts is the segregati12on of solid and liquid phase, gas, oxidation inclusions and other defects. Different semi-solid die casting process will affect the flow state and defect size at the location of different semi-solid metal melt coming together. By means of the process control and the mold structure optimization, “rewelding ” defects can be removed from the product cavity. The aluminum alloy semi-solid die-casting products with high performance are obtained finally.

Cooling Behavior and Microstructure of Semisolid A201 Aluminum Alloy Prepared by the SEED Process

The biggest challenge in semisolid processing of high-performance aluminum alloys is the narrow temperature processing windows of these alloys, and as a result, the preparation of qualified semisolid slurries is very important. High solid fraction slurries of high-strength A201 alloy were prepared by the Swirled Enthalpy Equilibration Device (SEED) process. The cooling behavior and microstructures of the A201 slurries produced by the standard, as well as a modified, SEED process were investigated. The results show that qualified A201 slurry can be produced by decreasing the pouring temperature and controlling the processing time in the SEED process. The modified SEED process significantly reduced the radial temperature gradient of the melt, due to the slow cooling rates involved, with the resulting slurries being more uniform, with more spherical microstructures, as compared to those produced by the standard SEED process. The formation of the nondendritic grain structure in the SEED process is attributed to the uniformly distributed large number of nuclei within the melt and the slow cooling of the melt in the containing crucible.

Effective cluster interactions and pre–precipitate morphology in binary Al-based alloys

The strengthening by coherent, nano-sized particles of metastable phases (pre-precipitates) continues to be the main design principle for new high-performance aluminium alloys. To describe the formation of such pre-precipitates in Al–Cu, Al–Mg, Al–Zn, and Al–Si alloys, we carry out cluster expansions of ab initio calculated energies for supercell models of the dilute binary Al-rich solid solutions. Effective cluster interactions, including many-body terms and strain-induced contributions due to the lattice relaxations around solute atoms, are thus systematically derived. Monte Carlo and statistical kinetic theory simulations, parameterized with the obtained effective cluster interactions, are then performed to study the early stages of decomposition in the binary Al-based solid solutions. We show that this systematic approach to multi-scale modelling is capable of incorporating the essential physical contributions (usually referred to as atomic size and electronic structure factors) to the free energy, and is therefore able to correctly describe the ordering temperatures, atomic structures, and morphologies of pre-precipitates in the four studied alloy systems.

Recent Progress and Development in Extrusion of Rare Earth Free Mg Alloys: A Review

Mg and its alloys are the lightest structural metals available and are extremely attractive for applications as lightweight components, particularly in the automobile, electronic, and aerospace industries. The global market for wrought Mg alloys has steadily expanded over the past decade. And numerous studies have been carried out to meet this increasing demand of high-performance Mg alloys. However, Mg extrusion alloys have had a very limited usage so far. To overcome existing industrial challenges, one desirable approach is the development of low-cost rare earth (RE) free Mg extrusion alloys with superior mechanical properties. This review will introduce the recent research highlights in the extrusion of Mg alloys, specifically focusing on low-cost RE-free Mg alloy. The results from both the literature and our previous study are summarized and critically reviewed. Several aspects of RE-free Mg extrusion alloys are described in detail: (1) novel alloying designs including Mg–Al-, Mg–Zn-, Mg–Ca-, Mg–Sn-, and Mg–Bi-based alloys, (2) advanced extrusion techniques, and (3) extrusion-related severe plastic deformation (SPD) processing. Accordingly, considering the large gap in mechanical properties between the current RE-free Mg alloys and high-performance aluminum alloys, new alloy design, processing route control, and recommendations for future research on RE-free Mg extrusion alloys are also proposed. We hope this review will not only offer insightful information regarding the extrusion of RE-free Mg alloys but also inspire the development of new Mg extrusion technologies.

Microstructure of High-Performance Aluminum Alloy Surface Processed by the Single-Excitation Same-Frequency Longitudinal⁻Torsional Coupled Ultrasonic Vibration Milling.

The high performance of parts is determined by the microstructure of the machined surface to some extent. Different processing methods have been used to construct different microstructures on machined surfaces; the effective improvement of the serviceability of parts has been the focus of research in the field of precision and ultra-precision machining. In the presented work, a microscratch was formed on the machined surface in ultrasonic assisted machining, and the surface microstructure of high-performance aluminum alloy processed by single-excitation rotational longitudinal–torsional coupled ultrasonic vibration (LTCUV) milling was investigated. First, the motion paths model of the cutting edge in the LTCUV milling were established; then, the single-excitation LTCUV milling system has been set up, and the acoustic performance of the LTCUV system was examined. The surface microstructure of aluminum alloy was processed by different machining techniques, and the effect of processing parameters on the surface microstructure and performance were investigated by the orthogonal design of experiment (DOE). The surface roughness was found to be proportional to the ultrasonic cutting speed and feeding rate. The surface roughness was mainly controlled by the ultrasonic amplitude, and the optimal surface quality corresponded to the ultrasonic amplitude of 4 μm. The cutting speed contributes greatly to the surface roughness. The water contact angle of surfaces obtained by ultrasonic processing was larger than that of surfaces achieved by the conventional processing, while the surface water contact angle was negatively related to the ultrasonic amplitude. Once the rotation speed exceeded a critical level, the ultrasonic amplitude exerted a negligible effect on the surface water contact angle. The cutting speed contributes the most to the water contact angle. The friction coefficients of surfaces treated by ultrasonic processing were lower than those obtained by conventional processing at constant processing parameters, while the friction coefficient was minimized at the ultrasonic amplitude of 4 μm. In the case of grease lubrication friction, the surface wear decreased with the ultrasonic amplitude, indicating the improved wear resistance of the processed surfaces. Similarly, the ultrasonic amplitude has the highest contribution rate to friction and wear.

Tightly binding valence electron in aluminum observed through X-ray charge density study

Accurate and high reciprocal resolution experimental structure factors of aluminum were determined from a synchrotron powder X-ray diffraction data measured at 30 K with sin θ/λ < 2.31 Å−1. The structure factors have small deviations from independent atom model in sin θ/λ < 0.83 Å−1. Theoretical structure factors were prepared using density functional theoretical calculations by full potential linearized augmented plane wave method. The deviation between experimental and theoretical data was also observed at around sin θ/λ ≈ 0.4 Å−1. The charge density was determined by an extended Hansen-Coppens multipole modeling using experimental and theoretical structure factors. Charge density maxima at tetrahedral site were observed in both experimental and theoretical deformation density. The charge-density difference peaks indicating directional bonding formation were observed in the difference density between experiment and theory. The present study reveals tight binding like character of valence electron of aluminum. The fact will provide a crucial information for development of high-performance aluminum alloy.

Tailored material properties using textile composites

Lightweighting is essential for the reduction of energy consumption in transportation. The most common approach is through the application of high specific strength and stiffness materials, such as composites and high performance aluminum alloys. One of the challenges associated with the use of advanced materials is the high cost. This paper explores the opportunities of using hybrid composites (glass and carbon, for example) with selective fiber placement to optimize the weight subject to price constraints for given components.Considering the example of a hat-section for hood reinforcement, different material configurations were modeled and developed. The required thickness of the hat section to meet the same bending stiffness as an all carbon composite beam was calculated. It was shown that selective placement of fiber around the highest moments results in a weight savings of around 14% compared to a uniformly blended hybrid with the same total material configuration. From this it is possible to estimate the materials cost of the configurations as well as the weight of the component. To determine which is best it is necessary to find an exchange constant that converts weight into cost – the penalty of carrying the extra weight. The value of this exchange constant will depend on the particular application.

Opportunities for aluminum-based nanocomposites

High performance aluminum alloys are conventionally made by heat treating alloys containing a variety of alloying elements in solid solution. Key performance attributes are controlled at the microstructural level by tailoring sizes and morphology of nano-sized second phases. This enabled the successful development of aluminum alloys having properties optimized in strength, damage tolerance and corrosion resistance. However, this process is naturally limited by the solubility of alloying elements in the aluminum matrix. In real world products, significant effort is deployed to achieve a homogeneous distribution of the alloying elements both at the macro and micro scales. Despite these efforts, heat treatable alloys can exhibit chemical gradients at grain boundaries, resulting in sub-optimized properties. Additionally, due to the very nature of the strengthening mechanisms, the properties of heat-treatable alloys are decreasing when exposed to elevated temperatures. To step outside the boundaries given by the solubility of alloying elements in the aluminum matrix, the extrinsic addition of nano-sized particles to the aluminum matrix is being evaluated.

アルミニウム合金のナノクラスタ制御と高性能化の研究

アルミニウム合金のナノクラスタ制御と高性能化の研究

Effect of Ultrasonic Vibration and Applied Pressure on the Microstructure and Mechanical Property of Al-5.0Cu-0.6Mn-0.6Fe Alloys

Al-5.0Cu-0.6Mn-0.6Fe alloy was obtained for the first time using ultrasonic vibration and squeeze casting simultaneously. The effect of ultrasonic vibration and applied pressure on the microstructures and hardness of Al-5.0Cu-0.6Mn-0.6Fe alloy were studied. The results indicated that the ultrasonic vibration and applied pressure promoted the formation of smaller α-Al globular grains. In particularly, with the treatment of ultrasonic vibration or applied pressure during solidification, the brittle Fe-rich imtermetallic compounds in Al-5.0Cu-0.6Mn-0.6Fe alloy became more refined and changed from Chinese script shape to polyhedral shape, which improved the mechanical property. Furthermore, these effects on the grain refinement and Fe-rich intermetallic compounds became more significant by using ultrasonic vibration and applied pressure concurrently during solidification. This process technology is helpful for the development of high performance aluminum alloys with low cost as well as for green casting.

Design of novel high-performance Al–Cu–Mg alloys containing Zn and Li

To design novel high-performance aluminium alloys, the properties and microstructure of Al–4.2Cu–1.4Mg alloy containing Zn and Li have been investigated by tensile tests, fatigue crack propagation test, slow strain-rate tensile test, Kahn tear test, scanning electron micrography and transmission electron micrography. The stress corrosion cracking resistance and toughness of Al–4.2Cu–1.2Mg alloy can be markedly improved by small Zn addition. Independent Li addition has no significant effect on the corrosion resistance of Al–4.2Cu–1.2Mg alloy, but the tensile strength is improved and the fatigue crack propagation is restrained. Small Zn addition promotes the precipitation of S′ phase during age treatment, and the grain boundary precipitates are scarcer than those of the base alloy. The co-effect of Li and Zn addition promotes the fine and dispersed precipitation of the S′ (non-equilibrium Al2CuMg) phases in Al–4.2Cu–1.2Mg alloy. The comprehensive performance (the fracture toughness, tensile properties, stress corrosion resistance and fatigue crack propagation resistance) of Al–4.2Cu–1.2Mg alloy with 0.25% Zn and 1.0%Li is outstanding. This alloy could lay the foundation for the design of new aluminium alloys.