High Strength Aluminum Alloy Research Articles

Сравнительный анализ химического состава и механических свойств различных участков сварного соединения дюралюмина, полученного сваркой трением с перемешиванием

Friction stir welding is an advanced method of joining various metals and alloys in the aircraft and mechanical engineering industries. This type of welding is used to join materials that are difficult to weld or not weldable by conventional methods. The high-strength D16 aluminum alloy is difficult to weld by fusion, which is associated with the formation of a dendritic structure in the fusion zone leading to a decrease in the mechanical strength of the joint. In the work, the microstructure and microhardness of a welded seam of the D16 aluminum alloy produced by friction stir welding was studied. Using scanning electron microscopy and optical metallography, the authors identified the presence of three zones: the weld core, the thermomechanical impact zone, and the heat effected zone. In the central part of the welded joint (in the core), a laminated onion ring structure was discovered. A change in the chemical composition of the aluminum solid solution was identified in different areas of the weld zones, as well as the presence of a concentration gradient within each zone. In the upper part of the welded seam, the solid solution is silicon-enriched and depleted in copper. Due to the solid solution depletion in alloying elements, the aluminum content in the solid solution in the zone of the welded joint is higher compared to the initial state. The microhardness values in different areas of the welded joint correlate with changes in the chemical composition. In the welded joint zone, a significant decrease in microhardness was found compared to the initial state, and a change in microhardness associated with the chemical composition gradient within each zone was also observed.

Mechanical characteristics of dissimilar friction stir welding processes of aluminium alloy [AA 2024-T351 and AA 7075-T651

Aerospace industries have remained dependent on aluminium alloys for airframe structural components manufacturing due to their superior strength, fracture toughness, and ability to resist corrosion. Especially, AA2024 and AA7075 have been the most prominent and timely tested robust aluminium alloys in these manufacturing sectors. However, joining these aluminium alloys through conventional fusion welding is difficult. The present investigation focused on the mechanical and metallurgical properties of these high-strength dissimilar aluminium alloys 2024-T351 and 7075-T651 using a Friction Stir Welding (FSW) process. The effects of factors such as rotational speed RS (800–1200 rpm), welding speed WS (20–60 mm/min), and tool plunge depth (0.2–0.4 mm) on the ultimate tensile strength (UTS) and yield strength (YS) have been evaluated. The experimental procedure employed is based on RSM. The fractured surface morphology was investigated using SEM. The investigation result showed higher tensile strength (147 MPa) at the combination of welding parameters (1200 rpm, 60 mm/min, and 0.4 mm). The fabrication industries became the great beneficiaries of this emerging technology of the FSW.

Ultrasound-assisted material characterization: An innovative method for the non-destructive in-situ detection of microstructural changes of high-strength aluminum alloys

The use of aluminum alloys in conjunction with thermal-assisted forming techniques permits the production of high-strength and geometrically complicated components without failure. By using innovative, temperature-dependent production techniques, it is possible to manufacture components with tailored properties. So far, however, it is not possible to characterize the microstructural behavior under thermal and mechanical load in real-time. Using a novel characterization method, which is based on the principle of laser ultrasonic testing, it has become possible to record contact-free and non-destructive microstructural changes in-situ during thermo-mechanical treatment. This allows the interaction-free detection of thermal as well as mechanical effects during thermal-supported forming operations. In this research work, the temperature-dependent behavior during the quenching and aging process of the precipitation-hardenable aluminum alloy AA6082 for a tailor-quenched forming process is recorded in real-time using laser ultrasonic techniques. First, the effects of different tool temperatures on quenching rates and material properties were investigated using conventional characterization methods, including temperature measurement, hardness and tensile tests. It was shown that a die temperature of 325 °C leads to the lowest material hardness and strength. Subsequently, the results were compared with the novel, non-destructive in-situ testing method and validated using microstructural analysis. It was proven, that microstructural changes can be identified during varying quench and aging operations. Thus, the influence of different process parameters on the microstructural and mechanical development of aluminum components can be detected in-situ for the first time.

DED Joining Process and Ultrasonic-Assisted Performance Optimization of High-Strength Aluminum Alloys Manufactured by SLM

DED Joining Process and Ultrasonic-Assisted Performance Optimization of High-Strength Aluminum Alloys Manufactured by SLM

Mechanical properties prediction of high-strength aluminium alloy components formed under the PHF process

Pre-strengthening hot/warm forming (PHF) technology can effectively shorten the microstructure evolution process of aluminium alloy deformation and heat treatment, and has a broad application prospect. In this paper, the process parameters in PHF are abstracted into sequence data, which is used as the input of long short-term memory neural network (LSTM) model to predict mechanical properties of aluminium alloy components after PHF process. Besides, the prediction models based on Random Forest (RF), Support Vector Regression (SVR) and Back Propagation Neural Network (BPNN) are established and compared with LSTM model. In addition, a Few-Shot Learning method based on the constitutive model is proposed to predict the properties of aluminium alloys.

Reinforcement of High-Strength Aluminum Alloy Structures by Steel Inserts

Reinforcement of High-Strength Aluminum Alloy Structures by Steel Inserts

Advanced wrought Mg-4.5Al-2.5Ca-0.02Mn (at%) alloys with exceptional balance of high thermal conductivity, yield strength, ductility, nonflammability, and corrosion resistance

Advanced wrought Mg-Al-Ca-Mn alloys were developed, demonstrating an outstanding array of technical advantages due to the remarkably high negative mixing enthalpy of an Al and Ca pair. This was achieved through meticulous optimization of alloy composition, heat treatment procedures, and extrusion parameters. The primary alloy under consideration was designated as Mg-4.5Al-2.5Ca-0.02Mn (at%). While maintaining a low density of 1.76 g/cm3, this alloy exhibited an exceptional properties profile, comprising a high thermal conductivity up to 124 Wm−1K−1 (approximately 79% of pure magnesium), a high tensile yield strength of 397 MPa (surpassing the high-strength aluminum alloy 7075-T6, by 25% in specific tensile yield strength), a notable tensile elongation of 5.5%, and remarkable nonflammability with a high ignition temperature of 1355 K. Finally, its corrosion resistance was twice that of the AZ91D alloy. The microstructure of the developed alloy system comprised α-Mg, eutectic C36 and C14 compounds, and precipitated C15 compound. The enhanced thermal conductivity was attributed primarily to the purification of the α-Mg matrix, facilitated by C15 plate precipitation during the heat treatment process. The superior mechanical properties were associated with the refinement of the α-Mg phase grain structure and the uniform dispersion of fine compounds achieved through extrusion. Based on the findings derived from this experimental study, a novel approach to designing multifunctional magnesium-based alloys has been formulated; that is, high thermal conductivity and high strength are attainable in plastically deformed Mg alloys composed of element pairs with a negatively high mixing enthalpy.

Changes in the structure and mechanical proper-ties of the aluminum alloy of the Al–Mg–Sc system as a result of treatment with a complex nanomodifier

Problem. On the basis of domestic and foreign research and the analysis of physicochemical properties of elements, the choice of scandium as a microalloying element of high-strength aluminium alloys is substantiated. The main criteria for the ability of scandium and its advantages over transition metals are given. Goal. The purpose of the work is to study the influence of a complex nanomodifier on the change in the structure and mechanical properties of aluminium alloy 1545 of the Al–Mg–Sc system. Methodology. For the first time, the treatment of aluminium melt with a complex nanodisperse modifier of the composition Mg2Si+SiС was proposed. The strength properties of aluminium alloys are significantly influenced by the size of the particles of the strengthening phase. Industrial experiments using dispersed particles of Mg2Si+SiС in a wide range of sizes of 50-100 nm. 
 Results. The technology of modifying aluminium melt with a complex modifier has been developed. Originality. A homogeneous structure of the modified alloy 1545 with a grain size 2.7 times smaller than the original state was achieved. Practical value. In the work, the grain size was determined and it was established that the grain size of alloy 1545 was 15.6 mm2 before modification, and 5.7 mm2 after modification. As can be seen from the given data, as a result of the modification, the grain structure of alloy 1545 was crushed by 2.7 times. It was established that the maximum values of σ0.2 and σv correspond to the optimal content of the powder composition: 0.10% with a further increase of the modifier, the strength properties decrease, while the increase in the strength properties of the modified alloy is 12...18% compared to the initial state.

Effect of Zn/Mg ratio on aging precipitates and mechanical property of high Mg content Al-Mg-Zn alloys with Sc and Zr additions

To enhance the strength of traditional 5xxx series alloys, this work designed Al-Mg-Zn alloys with high Mg content and different Zn/Mg ratios (wt%, Zn/Mg ratio<1.0) drawing inspiration from aging precipitation strengthening of 2xxx or 7xxx series aluminum alloys and thermodynamic calculation. Measurement of density, microhardness and tensile property as well as electron backscatter diffraction (EBSD) and high-resolution transmission electron microscopy (HRTEM) were used to investigate the effects of four different Zn/Mg ratios on the aging precipitation behavior and mechanical property of the studied alloys. As Zn/Mg ratio increases, both N3 (Zn/Mg = 0.37) and N4 (Zn/Mg = 0.71) precipitate fine and dispersed distributed nano T-Mg32(Al,Zn)49 precipitates. After a two-step aging treatment process of 90 °C/24 h + 140 °C/8 h, N4 exhibits tensile strength of 595.5 MPa, yield strength of 484 MPa, and elongation of 10.2% in the peak state. N4 features higher specific strength and lower density compared to the popular 7075-T6. The TEM analysis reveals that the addition of trace Sc and Zr leads to the formation of Al3(Sc,Zr) precipitates, which significantly refines grain size thus enhancing strength. The primary strengthening mechanisms of Al-Mg-Zn-Sc-Zr alloy include grain boundary strengthening, solid solution strengthening, and precipitation strengthening. A yield strength model considering multiple strengthening mechanisms and thermodynamic calculation has been adopted to achieve accurate yield strength predictions. This work provides reference for composition design, microstructure and property regulation of lightweight high-strength aluminum alloys.

The Effect of Point Defects on Young’s Modulus of the Off-Stoichiometric Al3X (X = Li, Sc, and Zr) Phases: A First-Principles Study

L12-Al3X (X = Li, Sc, and Zr) precipitates are the main strengthened phases of high-strength aluminum alloys and are critical for aerospace structural materials. Point defects and substitutional ternary elements change the mechanical properties of Al3X. In this paper, the effect of point defects, including vacancy, antisite, and substitutional element addition defects on the elastic modulus of the off-stoichiometric Al3X (X = Li, Sc, and Zr) phase were investigated by using first-principle calculations. The formation enthalpies of the defective Al3X alloy and isolated point defects in Al3X were calculated, and the results showed that the defects have an effect on the structure and elasticity of the off-stoichiometric Al3X phases. The lattice distortion, elastic constants, and elastic moduli were further investigated. It was found that the point defects increased the Young’s modulus for Al3Zr, and the doping of Er improved the Young’s modulus for off-stoichiometric Al3Li and Al3Sc. Adjusting the position of vacancies can improve the elastic modulus. In addition, the doping of substitutional elements (especially Sc, Ti, Zr, Hf, Ta, Mn, Ir, and Cf) can greatly increase the Young’s modulus of off-stoichiometric Al3Li.

Towards high strength and ductility of Al–Cu-Mg alloy via cyclic and monotonic pre-straining followed by ageing

This article presents an investigation of the ageing response of modern high-strength aluminium alloy 2519 (Al–5.64Cu-0.33Mn-0.23Mg-0.01Si (wt%)) after cyclic strengthening (CS). The impact of the pre-straining value on the mechanical properties, microstructure and phase composition was elucidated via hardness and tensile testing, analytical transmission and orientation imaging electron microscopy. The results show that cyclic hardening has a significant impact on the ageing behaviour of the alloy. Applying cyclic pre-straining in conjunction with monotonic enhances strength and ductility at once. This novel high-performance treatment results in superior strength-ductility combination. The improved mechanical properties are attributed to the observed changes in microstructure. The introduction of vacancies and dislocations, by repetitive and elastic straining before artificial ageing, leads to great homogeneous structure and an increase in the number density and volume fraction of the main strengthening phases (θ′ and Ω) and clusters/zones. Therefore, this work should suggest a strategy for developing a novel treatment of aluminium alloys with excellent mechanical properties.

Behaviour of aluminium/steel hybrid RSW joints under high cycle fatigue loading

The lightweight construction of automotive car bodies is the more important to reduce the fuel consumption and costs. High-strength steels and aluminium alloys are suitable for achieving these aims. Recent car bodies contain both materials, therefore necessary to make reliable joints between them. The resistance spot welding (RSW) can be used for joining of car bodies and it is applicable for aluminium/steel hybrid joints, too. High cycle fatigue (HCF) test results can be rarely found in the literature while HCF loading basically determines the lifetime of hybrid joints. 5754-H22, 6082-T6, and DP600 base materials were used for similar and hybrid RSW joints and HCF tests were performed. Number of cycles to failure values, failure modes, furthermore brittle intermetallic compound (IMC) layers were studied and analysed. In both aluminium/steel hybrid joints, the HCF test results showed better endurance limit like concerning aluminium/aluminium similar joints, but worse than steel/steel joints. For 5754-H22 alloy the endurance limit values are 648 N, 939 N, and 1285.5 N, for similar aluminium, hybrid, and similar steel joints, respectively. For 6082-T6 alloy these values are 513 N, 625.5 N, and 1285.5 N, respectively. In case of similar joints only base material fracture happens, but hybrid joint specimens show different failure modes. Base material fracture and shearing after partial base material fracture were typical failure modes in case of 5754-H22/DP600 and 6082-T6/DP600 hybrid joints, respectively. The full and partial plugging as a failure modes appeared for hybrid joints, too. The IMC layer characteristics showed opposite results in cases of hybrid joints, both the layer thicknesses of the shared and plugged joints and the thickness differences between the inner and outer parts of the joints were different.

Research Progress of Aluminum Alloy Welding/Plastic Deformation Composite Forming Technology in Achieving High-Strength Joints.

Fusion welding causes joint deterioration when joining aluminum alloys, which limits the use of aluminum alloy components in high-end equipment. This paper focuses on an overview of how to achieve high-strength aluminum alloy welded joints using welding/plastic deformation composite forming technology. The current technology is summarized into two categories: plastic deformation welding and plastic deformation strengthening. Plastic deformation welding includes friction stir welding, friction welding, diffusion welding, superplastic solid-state welding, explosive welding, and electromagnetic pulse welding. Plastic deformation strengthening refers to the application of plastic deformation to the weld seam or heat-affected zone, or even the whole joint, after welding or during welding, including physical surface modification and large-scale plastic deformation technology. Important processing parameters of plastic deformation welding and their effects on weld quality are discussed, and the microstructure is described. The effect of plastic deformation strengthening technology on the microstructure and performance evolution, including the hardness, tensile strength, fatigue property, residual stress, and hot cracking of aluminum alloy welded joints, and its evolution mechanism are systematically analyzed. Finally, this paper discusses the future development of plastic deformation strengthening technology and anticipates growing interest in this research area.

Coaxial Wire Laser-based Additive Manufacturing of AA7075 with TiC Nanoparticles

AA7075 is a heat treatable aluminium alloy widely used in aerospace and automotive applications due to its outstanding high strength-to-weight ratio. However, the implementation of this alloy in Additive Manufacturing (AM) processes has been limited due to its susceptibility to hot cracking. Moreover, selective evaporation of low boiling point elements Zn and Mg can cause gas porosity and diminish the mechanical properties of AM parts. Recent research revealed the effectiveness of nanoparticles additives to change the solidification behaviour of high-strength aluminium alloys and improve their weldability/printability. In this study, AA7075 enhanced with TiC nanoparticles was utilized as wire feedstock to create single and multi-layer samples with coaxial laser-directed energy deposition (L-DED). The response of the samples to precipitation hardening was studied, evaluating the microstructure and the microhardness before and after T6 heat treatment. Specimens were characterized using optical and electron microscopy and electron backscatter diffraction (EBSD). Crack-free and virtually porosity-free samples were fabricated, which exhibit a refined equiaxed grain structure with grain size <10μm. This confirms the ability of TiC nanoparticles to prevent columnar dendritic growth and promote heterogeneous nucleation. Microhardness values increased by 51 HV after T6 heat treatment and were uniform across the sample. Energy Dispersive Spectroscopy (EDS) analysis showed that there are evaporation losses of Zn and Mg. Considering the boiling temperatures of these elements, it is inferred that the molten pool reaches temperatures above 1090°C, and the partially melted zone temperature is between 907°C and 1090°C.

Integrating reversion ageing and forming of high-strength Al alloys: Principles and theoretical basis

Simultaneously improving the formability and post-formed strength of high-strength aluminum (Al) alloys, such as Al–Zn–Mg–Cu alloys, is essential in manufacturing complex-shaped panel components. The strict requirements on heat-treatment condition and high tooling costs limit the applications of current forming methods. A novel process called integrated reversion ageing and forming (IRAF) is proposed to form naturally aged (NA or T4 tempered) Al alloys. A principle-based concept analysis and systematic thermo-mechanical-metallurgical study of the IRAF process were performed. Additionally, tensile tests were conducted to evaluate the effects of parameters including heating rate, holding time, and forming temperature on formability and baked strength. The deformability of the AA7075-T4 alloy can be significantly enhanced through rapid heating to the reversion ageing temperature (150–300 °C), followed by short-term holding, as evidenced by the reduced yield strength of 200 MPa and increased uniform ductility. An instant strength increase to a value close to that of the T6 state was obtained after a short bake hardening (BH) treatment. Further, temperature-time-property (TTP) diagrams were established based on the correlation between the measured mechanical properties and through-process microstructure evolution to explain the mechanism underlying the optimised processing window of IRAF. The results indicate that fast-heating rate (>300 °C/min) promotes the reversion of NA clusters and inhibits re-precipitation of solutes, thereby improving the warm formability. Reversion ageing above 240 °C could induce the formation of coarse η'/η phases, leading to a considerably declined BH response. To accurately predict the strength evolution and deformation behavior during IRAF, a physical-based unified constitutive model was constructed by considering the reversion of NA clusters and solute re-precipitation. The bending and drawing tests on the AA7075-T4 alloy sheets verified that IRAF in the most-reverted state enabled optimum formability. The findings inspire promoting the reversion of pre-existing metastable particles to improve warm formability and post-formed age hardening.

Processability and Solidification Microstructure of Al-10Si-4.5Mg Alloy Fabricated by Laser Powder Bed Fusion

With the aim of developing a high-strength aluminum alloy for laser powder bed fusion (L-PBF), an Al–10Si–4.5Mg alloy with the a-Al/Si/Mg2Si three-phase microstructure was investigated. The Al–10Si–4.5Mg alloy processed by L-PBF exhibited a fine cellular microstructure including fine granular Mg2Si phases, and therefore exhibited a higher hardness of 187 HV0.1 than those of the conventional Al–Si–Mg alloy. However, cracks were macroscopically propagated between the internal fabrication voids along the melt pool boundaries in the L-PBF processed samples, resulting in a limited relative density below 95.5%. The cracking could be attributed to the relatively coarse Mg2Si particles decorated with the eutectic network. Although the improved strength suggests the advantage of strengthening by the Mg2Si phase, further optimization of the processing conditions will be required to manufacture the intact L-PBF parts.

The Influence of the Deposition Speed during Friction Screw Extrusion Additive Manufacturing of AA6060

Solid-state additive manufacturing may solve critical issues typically arising during fusion-based additive manufacturing of high-strength aluminium alloys. In this work, the recently introduced Friction Screw Extrusion Additive Manufacturing (FSEAM) process was employed to manufacture wall-like rectangular builds of AA6060 T6 deposited with deposition speeds from 300 mm/min to 500 mm/min. All builds were manufactured at a tool rotation rate of 400 rpm with 1 mm layer thickness. The volumetric supply rates were adjusted to maintain constant build width. Solid builds were formed without major defects over the full range of deposition speeds. The process generated sufficient normal force and heat at all deposition speeds which resulted in manufacturing of defect free builds. The resulting average grain size was consistently below 5 micrometer throughout all builds independent of deposition speed or location through the height. Microhardness measurements revealed a decrease in hardness from a feedstock value of 80 HV to around 50 HV in all manufactured builds. Tensile tests in the building direction showed consistent results for all the samples as a result of defect-free parts, demonstrating a tensile strength of approximately 150 MPa, yield strength of 100 MPa, and uniform elongation of 12-15%. The fracture surfaces revealed large amounts of dimples at all deposition speeds in line with the high degree of plastic deformation preceding fracture observed from the tensile tests. The obtained results indicated that FSEAM is a promising process for solid-state additive manufacturing of aluminium alloys.

Crack-free high-strength AA-7075 fabricated by laser powder bed fusion with inoculations of metallic glass powders

High-strength aluminum alloy is widely utilized in aerospace field. The primary thrust of this work was to overcome the issue of hot cracking of AA-7075, which occurs during laser powder bed fusion (LPBF) processing. By employing an innovation inoculation treatment with 5 wt % Zr50.7Cu28Al12.3Ni9 metallic glass (MG) powders, highly dense (relative density >99.2 %) and crack-free composite specimens of AA-7075/MG were successfully fabricated within a broad printing range. The as-printed AA-7075/MG composite specimens exhibited a uniform microstructure with the fine equiaxed grains and the crack mitigation was attributed to the grain refinement, which decreased from 9.9 μm to 0.564 μm after addition of MG powders. The inoculation treatment of MG powders triggered the in-situ formation of Al3Zr particles on the one hand, promoting the formation of fine equiaxed grains with random orientation. On the other hand, in-situ formed nano-sized amorphous particles formed due to the high glass-forming ability of Zr-based MG and rapid cooling rate during LPBF process could strengthen the alloy. The as-printed AA-7075/MG composite specimens exhibited a compressive strength exceeding 1.5 GPa. Meanwhile, it exhibited the highest ultimate tensile stress and yield strength of 513 MPa and 488 MPa, respectively, with an elongation of over 9 %. The excellent mechanical properties are ascribed to a synergistic combination of grain boundary strengthening, precipitation strengthening induced by Al3Zr nanoparticles, solid-solution strengthening, and the effective obstacle of dislocation motion by the nano-sized amorphous particles. The current work presents a novel and cost-effective approach to producing crack-free, high strength aluminum engineering components using LPBF.

Effect of Nickel Addition on Solidification Microstructure and Tensile Properties of Cast 7075 Aluminum Alloy

In order to explore the casting technology of a high–strength aluminum alloy, the effects of nickel on the solidified microstructure and tensile properties of a 7075 aluminum alloy were studied. 7075 aluminum alloys without nickel and with 0.6% and 1.2% nickel were prepared by a casting method. The results showed that the increase of Ni content in the 7075 alloys increased the liquidus temperatures, primary α (Al) grains were refined significantly, and the divorced eutectic structure was gradually formed among α (Al) grains with the preformation of the Al3Ni phase. In comparison, the 7075 alloy with 0.6% nickel content had less intergranular shrinkage porosity, and its elongation and ultimate tensile strength was enhanced 45% and 105% higher than those of the as-cast 7075 aluminum alloy, respectively. When the Ni content was increased to 1.2%, the eutectic phases of the alloy became much coarser compared to the other two alloys, and the mechanical properties obviously reduced too.

Mechanical properties and microscopic mechanisms of 2219-T6 aluminum alloy under dynamic tension with cryogenic temperatures

The 2219-T6 aluminum alloy has poor plastic deformation ability at room temperature, which makes it difficult to satisfy the forming requirements. This study combined high strain rate and cryogenic temperature to improve the formability of aluminum alloys. Dynamic tensile experiments using Split-Hopkinson tensile bar combined with cryogenic temperatures have shown that the ultimate strength and fracture elongation at 2000 s-1 with -160 °C is 482 MPa and 29.0%, respectively, representing a substantial increase of 31% and 125%, respectively, compared to quasi-static tension at 25 °C. By analyzing the microstructure, the results show that more uniform micro-deformation behaviors occurred due to the activation of multi-slip at high strain rates with cryogenic temperature. The high strength is due to the formation of a multitude of dislocations and substructures. Dislocation networks caused by the increasing cross-slip frequency increase the strength and guarantees stable plastic flow. It also leads to local shear fractures due to the increased velocity of dislocations movement and inhibited propagation of voids. This study provides the fundamental researches for understanding the superior mechanical properties of high-strength aluminum alloys at cryogenic temperatures in the area of high-speed forming and for addressing the challenges associated with forming these alloys directly in their service state.