Heat-resistant Aluminum Alloy Research Articles

Enhancing high temperature strength of wire arc directed energy deposition Al Cu heat-resistant aluminum alloy by precipitation of thermally stable phase

Enhancing high temperature strength of wire arc directed energy deposition Al Cu heat-resistant aluminum alloy by precipitation of thermally stable phase

Effect of aging state on microstructure and properties of heat affected zone in Al-Mg-Si-Cu alloy welded joints

The softening of the heat affected zone (HAZ) remains a significant challenge in fusion welding of novel Al-Mg-Si-Cu alloy, and the underlying mechanisms vary across different aging states. However, limited research has been conducted on this topic. Therefore, this study investigates the influence of various aging states on the microstructure and mechanical properties within the HAZ of welded joints by selecting extrusions treated with T4, T5, and T6 heat treatments. The results indicate that the increase in hardness of HAZ I is attributed to solid solution strengthening. In the HAZ I, the precipitated phases are mostly dissolved into the matrix under the influence of a peak temperature of 464.6 °C, and no residual precipitated phase is detected in T4 and T5 alloy joints, while some undissolved Q phase is observed in T6 alloy joint. The decrease in hardness of HAZ Ⅱ is attributed to the limited precipitation of coarse β" and Q' phases for the T4 alloy welded joints, which weakens the solid solution strengthening. However, the softening mechanisms in the HAZ Ⅱ of the T5 and T6 alloy joints are ascribed to the dissolution of β" and subsequent precipitation of Q' and Q phases. HAZ Ⅲ, close to the base metal, exhibits a lesser degree of influence and thus experiences a gradual recovery in hardness. This study can provide theoretical guidance for the exploration of high-strength, heat-resistant aluminum alloys.

Additive manufacturing of heat-resistant aluminum alloys: a review

Abstract The capability for synergistic advancements in both making and shaping afforded by additive manufacturing (AM) enables the flexible production of high-performance components. Boosted by the growing demand for heat-resistant aluminum alloys in the moderate-temperature weight-critical applications, AM of heat-resistant aluminum alloys constitutes a burgeoning field. Although numerous advances have emerged in recent years, there remains a gap in the review literature elucidating the newly-developed alloy systems and critically evaluating the efficacy. This state-of-the-art review presents a detailed overview of recent achievements on the heat-resistant aluminum alloy development. It begins with the introduction of various AM technologies and the pros and cons of each technique are evaluated. The enhancement mechanisms associated with printability and high-temperature properties of AM aluminum alloys are then delineated. Thereafter, the various additively manufactured aluminum alloy systems are discussed with regard to the microstructure, heat resistance and high-temperature performance. An emphasis is put on the powder bed fusion-laser beam (PBF-LB) as it has garnered significant attention for heat-resistant aluminum alloys and the vast majority of the current studies are based on this technique. Finally, perspectives are outlined to provide guidance for future research.

Effect of alloying elements on coexisting phases and microstructure of M174 heat-resistant aluminum alloy

Abstract This article mainly focuses on high-power density diesel engine piston alloys, with the main component system being M174 heat-resistant aluminum alloy. On this basis, the main heat-resistant alloying elements Cu, Ni, and Fe were optimized and designed. This article is based on Thermo-Calc thermodynamic software, and comprehensively calculates and analyzes the multi-component alloy equilibrium phase diagram and Scheil non-equilibrium solidification of Al-(4-6)Cu-(1.5-3)Ni-(0.7-1.1Fe)-12.5Si-0.85Mg (mt.%) heat-resistant aluminum alloy system. Through the orthogonal experimental method of alloy composition, the phase distribution and microstructure composition of different alloy compositions are obtained. Research has found that Fe-rich phases such as Al5FeSi and Al9FeNi, as well as Ni-rich phases such as A13CuNi, A17Cu4Ni, and Al3Ni, are the main heat-resistant phases of the alloy in the temperature range of 350°C-420°C, providing important support for the high-temperature mechanical properties and creep damage resistance of piston aluminum alloy. At the same time, this article further studies the solidification history and microstructure precipitation of alloys. Fe-rich heat-resistant phases such as Al5FeSi and Al9FeNi have a higher solidification sequence. As primary and secondary phases, it is easy to generate coarse solidified structures. The organizational content is sensitive to the alloy composition. A13CuNi and A17Cu4Ni mainly precipitate in a multi-component eutectic structure, with layered and petal-shaped morphologies. The research results of this article have important theoretical significance and application value for the optimization design of high-power density piston aluminum alloy composition and the coordinated control of multi-phase structure.

Achieving high strength of Al-Cu-Li-Sc alloy over wide temperature range from 25 °C to 300 °C

Modern aerospace and transportation sectors have imposed more stringent requirements for high-strength aluminum alloys. Taking into account factors such as processing, assembly, maintenance, and recycling, there is a desire to develop one high strength aluminum alloy over wide temperature range from 25 °C to 300 °C, however, it is an ongoing challenge topic. Here, a novel Al-Cu-Li-Sc alloy with a reduced Cu content (∼2.8 wt%) was designed, exhibiting great yield strength with 482 MPa at 25 °C, 351 MPa at 200 °C, and 186 MPa at 300 °C, better than present commercial Al-Cu-Li alloys, Al-Cu-Sc alloys, due to the promotion of nucleation of T1 precipitates and their improved coarsening resistance. The novel Al-Cu-Li-Sc also overcomes the shortcoming of commercial Al-Cu-Li alloy which is the rapid degradation of mechanical properties after thermal exposure at 200 °C, as well as exhibiting comparable heat resistance to Al-Cu-Sc alloy after thermal exposure at 300 °C. This study offers a valuable engineering insight to develop light-weight, high-strength and heat-resistant aluminum alloys.

Analysis of the Phase Composition of the Al–Cu–Mn–Ca System as the Base for Heat-Resistant Aluminum Alloys

Analysis of the Phase Composition of the Al–Cu–Mn–Ca System as the Base for Heat-Resistant Aluminum Alloys

Revealing the coarsening behavior of precipitates and its effect on the thermal stability in Tʹ and ηʹ dual-phase strengthened Al-Zn-Mg-Cu alloys

High-strength Al-Zn-Mg-Cu alloys are widely utilized, but their strength deteriorates as strengthening precipitates coarsen rapidly at elevated temperatures, limiting their applications above 150°C. This study systematically investigates the microstructure evolution and its impact on the properties of peak-aged Al-Zn-Mg-Cu alloys with varying Zn/Mg ratios during thermal exposure at a series of temperatures from 150 to 300°C for 500 h. The results reveal that alloys A1 and A2 with an optimal Zn/Mg ratio (1.50−2.14) and relatively lower (Zn + Mg) content (7.0−8.8 wt.%), exhibit superior heat resistance properties compared to the other three alloys. Despite having lower strength relative to alloys with higher solute content, peak-aged alloys A1 and A2 retain the highest strength after thermal exposure. This performance is attributed to the high proportion (over 80%) of T′/T phases in the precipitates for alloys A1 and A2, which demonstrate better thermal stability in comparison to η′/η phases. Additionally, the lower solute content reduces the driving force for diffusion of Zn and Mg atoms, thus inhibiting the coarsening of precipitates. Moreover, the study elucidates that the coarsening mechanism of precipitates transitions from interfacial diffusion control at 150°C to matrix diffusion control at 200−300°C. These insights into the composition-dependent coarsening behavior of precipitates in dual-phase strengthened Al-Zn-Mg-Cu alloys offer valuable guidance for designing heat-resistant aluminum alloys with enhanced performance at elevated temperatures.

Analysis of compression response and coordinated deformation mechanism of bi-crystal Al-Cu-Mg-Ag alloy using CPFEM

In this paper, the compression behavior of Al-Cu-Mg-Ag bi-crystal samples at room temperature under different orientation combinations was studied. The stress-strain distribution of bi-crystal samples during the compression process was studied based on the crystal plastic finite element method (CPFEM). The deformation mismatch and slip transfer caused by the orientation combination of bi-crystal are discussed. The results show that the Al-Cu-Mg-Ag alloy bi-crystal samples with different orientations exhibit an anisotropic hardening response under compression. The combination of soft and hard orientation can coordinate the dislocation drive of the yield point, delay the elastoplastic transition of the yield point, and greatly improve the strength of the alloy. The mechanism of high strength of heterogeneous structure is proposed in this paper, which provides an important reference for the design of high strength heat resistant aluminum alloy for automobiles.

Розроблення жароміцних ливарних сплавів на основі системи Al-Fe-Mn-Ni

Development of new creep-resistant materials is a constantly existing task for modern materials science. At the same time, the creation of creep-resistant aluminum alloys plays an important role due to the combination of low density and the potential to achieve high resistance to properties degradation unter elevated temperatures. Increasing the level of operating temperatures for aluminum alloys makes it possible to replace some of the parts made of iron-based materials in cars, airplanes and various machinery. This will allow to reduce the weight of machines and mechanisms, increase their energy efficiency and environmental friendliness due to the reduction of carbon dioxide emissions. Most of the widely used creep-resistant aluminum alloys belong to the Al-Si-Cu, Al-Cu and Al-Si-Cu-Fe-Ni systems. Such alloys have a relatively low level of mechanical properties, which is insufficient for modern requirements. Their significant advantage is the ease of obtaining finished products by using casting processes. Among the alternative systems of heat-resistant aluminum alloys, those containing Fe, Ni, Cr and Mn are often considered. Iron and nickel are able to form fibrous nano-sized components of eutectics with aluminum, which are stable at high temperatures. They are effective barriers for the movement of dislocations and they also do not eliminate alloys plasticity. The disadvantage of such alloys is the zero alloying of the matrix metal, which means potentially low strength. Alloying of heat-resistant aluminum alloys should be carried out with elements that have a low diffusion coefficient in aluminum. The best option for this is manganese, which can dissolve in Al-matrix in a large quantities and forms a stable strengthening intermetallic Al6Mn with aluminum. Al-Fe-Mn-Ni alloys, because of their structural and phase features, can be subjected to plastic deformation, which, in combination with heat treatment, significantly increases the level of mechanical properties of alloys in a wide temperature range due to grain refinement and inhibition of recrystallization by stable ultradispersed intermetallic particles. Keywords: сasting aluminum alloys, creep-resistant alloys, new materials, Al-Fe-Mn-Ni.

Grain size control method for enhancing high-temperature durability of Al–Cu–Mg–Ag alloy

Reducing the grain boundary density (obtaining larger grain size) is beneficial for improving high-temperature durability of the heat-resistant aluminum alloys, and thus for extending their service life. In this paper, a grain size control method was proposed to enhance high-temperature durability of an Al–Cu–Mg–Ag alloy. A relationship formula between grain size, holding time, and annealing temperature was obtained through theoretical analysis. The recrystallization curve of a deformed Al–Cu–Mg–Ag alloy under different heating rates was determined through three-point bending thermal relaxation experiments. Based on the above relationship formula, the recrystallization kinetics parameters were obtained. Subsequently, based on actual processing conditions, the annealing temperature with the maximum grain size under a given annealing time was calculated. After the annealed sample underwent solution-aging (T6) treatment, the grain size increased by more than 60% compared with that of the directly solution-aging treated sample. This method can increase the duration by more than 60% at conditions of 210 °C/190 MPa without significantly reducing the room-temperature mechanical properties.

Enhanced high-temperature strength and ductility of wire arc additive manufactured Al–Ce–Mg alloys with fine α-Al/Al11Ce3 eutectics

Here, wire-arc additive manufacturing (WAAM) is employed to fabricate Al–Ce–Mg heat-resistant aluminum alloy, considering its capability to manufacture large complex structures more efficiently. Large-sized faceted Al11Ce3 intermetallic compounds are formed in the as-cast alloy with a hypereutectic microstructure. The microstructure is transformed to a eutectic microstructure by non-equilibrium solidification of WAAM, consisting lamellar α-Al/A111Ce3 eutectics. The WAAM alloy shows enhanced mechanical strength and ductility at 200 °C, compared with the as-cast alloy. The significant improvements of ultimate tensile strength and elongation for the WAAM alloy are correlated with its higher strain hardening rate, along with the transition from cleavage fracture to dimple fracture. The cracking of All1Ce3 particles occurs preferentially during the elastic deformation stage, as revealed by in-situ testing, and the strain hardening capability of the as-cast alloy is reduced. Pore defects, 0.15 % in volume fraction, are produced via WAAM processing, and the plastic deformation promotes the pore growth and mergence, increases the pore volume fraction, and decreases the pore sphericity. Our results demonstrate that WAAM is strongly attractive for the fabrication of Al–Ce–Mg alloys, due to the enhanced high-temperature strength-ductility synergy.

Research progress on microstructure tuning of heat-resistant cast aluminum alloys

AbstractWith development of present energy-saving society, lightweight and green development in the automotive and aerospace industries have put forward urgent demands for heat-resistant cast aluminum alloys. Present cast aluminum alloys are of lightweight and have excellent mechanical properties when serving in ambient environment. However, when serving at temperatures of 200–300 ℃ or even higher, the alloys inevitably soften and the high-temperature mechanical properties decline rapidly, hardly meeting the requirements for high-performance equipments. This paper summarizes the development process of classic heat-resistant aluminum alloys, especially the microstructural characteristics of heat-resistant cast aluminum alloys in the past decade, and reviews the current microstructure tuning strategies of heat-resistant aluminum alloys from the aspects of intrinsic heat resistance of the second phases, phase interface modification, diffusion-controlled phase transition, grain boundary stabilization and composite material design. Finally, we propose the prospects for the future development of heat-resistant aluminum alloys. Graphical abstract

Phase transformation and thermal stability of the laser powder bed fused high-strength and heat-resistant Al–Ce–Mg alloy

The coarsening of strengthening phases, phase transformations, and interface stability between these phases and the matrix play a crucial role in determining the strength, ductility, and heat resistance of aluminum alloys fabricated through additive manufacturing (AM). In this study, a heat exposure experiment at 400 °C for 1 h was conducted on the laser powder bed fused Al–Ce–Mg alloy. A comprehensive analysis of the microstructural evolution, phase composition, interfacial bonding strength, and mechanical properties before and after heat exposure was performed using synchrotron X-ray diffraction techniques, first-principles calculations, transmission electron microscopy, and mechanical testing. For the first time, a phase transformation from Al11Ce3 to Al4Ce was discovered. Some semi-coherent relationships of [301]Al11Ce3//[011]Al, (060)Al11Ce3//(00)Al were transformed into coherent relationships of [001]Al4Ce//[001]Al, (200)Al4Ce//(00)Al, and the interfacial energy was reduced by 4.385 J m−2. In-situ Al11Ce3 nano-networks after heat exposure were retained and Al4Ce nanoparticles contribute to the thermal stability of the alloy by hindering dislocation motion and grain coarsening. The strength of the heat exposure alloy reached up to 416 MPa, which is about 95 % of the strength of the as-fabricated state and the elongation increased from 9.3 % to 13.8 %. These results provide a new approach for the design of high strength-ductility synergy and heat-resistant aluminum alloys via AM.

A Study on the Influence of Zr on the Strengthening of the Al-10% Al2O3 Composite Obtained by Mechanical Alloying

Al2O3 is a traditional strengthening phase in aluminum matrix composites due to its high hardness and melting point. At the same time, zirconium is an important alloying element for heat-resistant aluminum alloys. However, its effect on the structure and properties of Al-Al2O3 composites remains unexplored at present. In this work, the effect of the addition of Zr (5 wt%) on the microstructure and strengthening of the Al-10 vol% Al2O3 composite was investigated for the first time. Composite materials with and without Zr addition were obtained through mechanical alloying as a result of ball milling for 20 h followed by multi-directional forging (MDF) at a temperature of 400 °C. OM, SEM and XRD were used to study the microstructure and its parameters. The work showed that the use of mechanical alloying and MDF contributes to the formation of dense composite samples with a nanocrystalline microstructure and a uniform distribution of alumina particles. The addition of Zr contributes to a 1.4-fold increase in the microhardness and yield strength of a compact sample at room temperature due to the formation of Al3Zr (L12) dispersoids. It was been shown that the largest contribution to the strength of both materials comes from grain boundary strengthening, which is at least 50% of the yield strength. The resulting composites exhibit high heat resistance. For example, their compressive yield strength at 350 °C is approximately 220 MPa.

Precipitating thermally reinforcement phase in aluminum alloys for enhanced strength at 400 °C

Heat-resistant aluminum alloys are widely used in aerospace and automotive fields for manufacturing hot components due to their advantages in lightweight design and energy conservation. However, the high-temperature strength of existing cast aluminum alloys is always limited to about 100 MPa at 350 °C due to coarsening and transformation of strengthening phases. Here, we reveal that the yield strength and ultimate tensile strength of the T6 state Al–8.4Cu–2.3Ce–1.0Mn–0.5Ni–0.2Zr alloy at 400 ℃ increase by 34% and 44% after re-aging at 300 °C for 100 h, and its thermal strength exhibits distinguished advantage over traditional heat-resistant aluminum alloys. The enhanced elevated-temperature strength is attributed to the reprecipitation of the Ni-bearing T-Al20Cu2Mn3 phase, whose number density increases over one time. The significant segregation of Ni, Ce, and Zr elements at the interfaces helps improve the thermal stability of the T phase. The thermostable T phase effectively strengthens the matrix by inhibiting dislocation motion. Meanwhile, a highly interconnected 3D intermetallic network along the grain boundaries can still remain after long-term re-aging at 300 °C, which is conducive to imposing a drag on the grain boundaries at high temperatures. This finding offers a viable route for enhancing the elevated-temperature strength of heat-resistant aluminum alloys, which could provide expanded opportunities for higher-temperature applications.

Microstructure and mechanical properties of Al–18Si–10Cu–10Ni–5Mn(-5Mg) heat-resistant aluminum alloys prepared by laser-directed energy deposition

The application of aluminum alloys in high-performance engines is challenging because they soften severely at high temperatures (above 300°C). In this paper, a new aluminum alloy composition design is proposed to fabricate Al–18Si–10Cu–10Ni–5Mn(-5Mg) alloys by a laser-directed energy deposition process (L-DED), which aims to form Mn-rich and Ni-rich phases with good high-temperature stability. The addition of Mg not only suppresses the tendency of selective growth of α-Al grains along the building direction but also induces the precipitation of the δ-Al3CuNi phase and Al15Mn3Si2 phase. In the L-DED-prepared Al–18Si–10Cu–10Ni–5Mn–5Mg alloy, the higher number of high-temperature strengthening phases and finer grains lead to higher microhardness compared with the forged 4032 aluminum alloy, which exhibits excellent high-temperature wear resistance. In addition, the tensile strength of Al–18Si–10Cu–10Ni–5Mn–5Mg alloy still reaches about 240 MPa at 350°C. This excellent high-temperature mechanical property is attributed to the rapid solidification producing ultra-high supersaturated solid solution and the formation of high-temperature strengthening phases such as Mn-rich and Ni-rich phases with uniform dimensions.

Improved stress relaxation stability of a heat-resistant Al-Cu-Mg-Ag alloy with good mechanical properties by a pre-annealing/solution-aging treatment

Good stress relaxation stability enables heat-resistant aluminum alloys to serve well at high temperatures. From the viewpoint of simultaneous regulation of microstructure and precipitates, a deliberate pre-annealing (200–400 ℃) followed by solution-aging (T6) treatment was proposed to improve the stress relaxation stability of an Al-Cu-Mg-Ag heat-resistant aluminum alloy in this work. A peak effect on the stress relaxation stability was found with a pre-annealing temperature of 325 ℃, which is associated with larger-sized grains and finer-sized precipitates of the alloy. This interesting peak phenomenon is attributed to a good balance of recrystallization and precipitation. Moreover, the regulated microstructure surprisingly assisted the 325 ℃ pre-annealing+T6 treated alloy with good tensile properties. The proposed heat treatment method provides a route for developing high-performance heat-resistant aluminum alloys.

First-Principles Study of the Structural, Mechanical and Thermodynamic Properties of Al11RE3 in Aluminum Alloys

The stability and mechanical and thermodynamic properties of Al11RE3 intermetallics (RE = Sc, Y and lanthanide La-Lu) have been investigated by combining first-principles and Debye model calculations. It was found that the formation enthalpies of the Al11RE3 intermetallics are all negative, indicating that they are stable; moreover, the experimental values of Al11La3 and Al11Ce3 are in good agreement with the predicted values, which are −0.40 kJ/mol and −0.38 kJ/mol, respectively. The calculated results of the mechanical properties reveal that the Young’s modulus E and shear modulus G of Al11RE3 (RE = La, Ce, Pr, Nd and Sm) intermetallics are obviously greater than that of Al, implying that the stiffness, toughness, and tensile strength of them are significantly greater than those of aluminum, and that they, as strengthen phases, can effectively improve the mechanical property of aluminum alloys. The Poisson’s ratio v of Al11Sc3 (0.37) is the largest, and the heterogeneity is obvious. All the Al11RE3 intermetallics can enhance the thermostability of the aluminum because of their lower Gibbs free energy F in the range of −5.002~−4.137 eV/atom and thermal expansion coefficient α of Al in the range of 2.34~2.89 × 10−5/K at 300K, as well as higher entropy and constant volume-specific heat than aluminum at finite temperatures. With an increase in the atomic number, different change trends were observed for the formation enthalpy ΔHf, bulk modulus B, Young’s modulus E, and shear modulus G. This paper can provide ideas and help for designing a high-performance, heat-resistant aluminum alloy.

Microstructural Characterization of the As-Cast and Homogenized Al-Cu-Mg-Ag Alloy

In this study, the as-cast microstructure and the evolution of the homogenized microstructure of large-scale industrialized Al-Cu-Mg-Ag heat-resistant aluminum alloy ingots were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive analysis (EDS), and differential scanning calorimetry (DSC). The results indicate that the dendritic segregation is evident in the ingot along the radial direction, and the grain boundaries are decorated with lots of net-shaped continuous eutectic structures. With the homogenization time extension and the homogenization temperature increase, the eutectic phases (i.e., the primary Al2Cu phase, the Al2CuMg phase, and the AlCuMgAg quaternary phase) at the grain boundaries gradually dissolve back into the matrix. Meanwhile, most of the dendritic grain boundaries gradually become sparse and thinner. Finally, it is found that the optimal homogenization regime of the Al-Cu-Mg-Ag alloy is 420 °C/5 h+480 °C/8 h+515 °C/24 h.

Study on optimization of heat-resistant conductor in line capacity expansion

Due to the low transmission capacity margin of overhead conductors of ACSR type in the existing grid structure, the large-scale grid connection of new energy is greatly limited. However, 60% of IACS heat-resistant conductors have low conductivity and high power loss in the transmission process. Therefore, 61.5% of IACS heat-resistant aluminum alloy conductors with high conductivity are developed for line capacity expansion and reconstruction. The feasibility of 61.5% IACS high conductivity heat-resistant aluminum alloy stranded conductor is analyzed in combination with the example of urban power line capacity expansion and transformation. Under the condition that the call height margin of the original line tower is sufficient, the use of this type of conductor can achieve obvious energy saving effect and effectively improve the transmission capacity and energy utilization rate of the line have been increased. Under the condition that the sag of the conductor and the bearing capacity of the tower do not increase compared with the original line, the capacity of the original line can be increased by at least 1.4 times by using this type of conductor. At the same time, because the conductor uses aluminum clad steel core as the reinforcing core, the corrosion resistance of the conductor is effectively improved to ensure the overhead transmission in coastal areas or heavily polluted areas safe operation reliability of electric lines.