Conventional Al Alloys Research Articles

Synergistic crack inhibition by lamellar structure and graphene nanoplatelets in 2024 Al-GNPs/TC4 laminated metal composites

Al/Ti laminated metal composites (LMCs) benefit from a bionic laminate structure that allows for simultaneous strength and plasticity enhancement. However, the Al layer with lower strength is always the first to crack under stress, resulting in declining mechanical properties of the Al/Ti LMCs. In this study, 2024 Al-GNPs/TC4 LMCs were prepared by replacing the conventional Al or Al alloy layers with 2024 Al-GNPs composites. Its ultimate tensile strength of 757 MPa surpasses that of almost all other Al/Ti LMCs. The lamellar structure and GNPs were found to have a synergistic effect in enhancing the mechanical properties by inhibiting crack extension across and within the layers, respectively. The hindrance of crack extension by the lamellar structure is primarily due to strain delocalization in TC4, as confirmed by phase-field-crystal simulation. On the other hand, GNPs impede crack extension through passivation and deflection, which was revealed by molecular dynamics to be attributed to dislocation hindrance and load transfer. Furthermore, it was confirmed that the main factors affecting the formation of intermetallic compounds are diffusion coefficient and solid solubility. This work provides new insights for breaking the performance limits of LMCs.

Advances in Synthesis and Characterization of Aluminum‐Based Amorphous Alloys: A Review

Aluminum‐based glassy alloys and composites exhibit more than two times higher tensile and compressive strength and superior corrosion resistance compared to the conventional Al alloys. However, the low glass‐forming ability (GFA) of Al‐based glass‐forming compositions restricts the synthesis of large dimension Al‐based amorphous alloys. In contrast, powder metallurgy route leads to synthesis of higher‐dimension Al‐based metallic glasses and composites. A detailed review on the efforts made to improve the dimension and mechanical properties of the Al‐based glassy alloys and composites is essential to further develop these materials for industrial applications. Researchers aspiring to develop high‐strength light‐weight materials can be benefited from such a detailed review on Al‐based amorphous alloys and composites. In this review article, a holistic approach is made to understand the GFA, crystallization behavior, corrosion resistance, and mechanical and electronic properties of Al‐based glassy alloys and composites. The effects of various alloying elements on GFA and criteria to optimize Al‐based glass‐forming alloy composition are discussed. The crystallization behavior is discussed with phase‐separation and quenched‐in nuclei models. The effects of various crystalline phases in the amorphous matrix on corrosion resistance and mechanical and electronic properties are discussed in detail.

Characterization and constitutive analysis-based crystal plasticity of warm flow and fracture behaviours of 2060 Al–Cu–Li alloy

AA2060-T8 is a relatively new Al–Cu–Li alloy developed in the last few years as a lightweight alternative to conventional Al alloys. Thus, it is essential to characterize the warm flow, fracture, and anisotropic behaviours of this alloy and propose constitutive analysis-based crystal plasticity (CP) modelling to link its mechanical behaviour with the microstructural state. Therefore, in this study, isothermal warm tensile tests were conducted using a Gleeble-3800 thermomechanical simulator and different sample orientations at temperatures and strain rates varying from 373 to 573 K and 0.001–0.1 s−1, respectively. The tensile behaviour of the 2060 Al–Cu–Li alloy sheet depends on the sample orientations, which results in significant anisotropy. The anisotropic degree of the tensile properties of this alloy was significantly reduced by increasing the forming temperature above 473 K. In addition, the fracture behaviours of 2060 Al–Cu–Li sheets were transformed from mixed ductile-brittle fracture mode to ductile fracture mode by decreasing strain rates and increasing the temperatures, respectively. Afterward, a novel crystal plasticity model was proposed to describe the grain behaviour and the deformation mechanism of 2060 Al–Cu–Li alloy under warm forming conditions. The developed constitutive model was implemented using the monolithic time-integration algorithm-based backward Euler method. The results acquired from the proposed constitutive analysis agree well with those obtained from experimentation in all testing conditions. This indicates its ability to accurately predict the warm flow behaviour of 2060 Al–Cu–Li alloy under different strain rates and loading directions.

Direct ageing of LPBF Al-1Fe-1Zr for high conductivity and mechanical performance

The novel Al-1Fe-1Zr alloy leverages the non-equilibrium solidification conditions characteristic of the laser powder bed fusion (LPBF) process, namely a high thermal gradient (G) and solidification front velocity (R). The multiscale characterization of its microstructure in as-built and peak-aged conditions by SEM, TEM with EDS and automated crystal orientation mapping (ACOM), brings new insights on alloy design for LPBF. The solidification conditions permit the solute supersaturation of Fe and Zr, with the latter precipitating as L12-Al3Zr nanoparticles following ageing, bringing a high strengthening contribution. In conventional Al alloy ingots, Fe tends to create coarse particles which are detrimental to ductility. Here the Fe particles show a fine globular morphology in the as-built condition, and fine faceted Fe-rich intermetallics are obtained upon ageing. Nanoindentation and in situ tensile tests in the SEM coupled with microscale strain measurements shed light on the relation between microstructural and strain heterogeneities in the as-built condition. Our characterization results for this new Al-1Fe-1Zr grade are synthesized into a simple model for its solidification upon LPBF. In particular, the origin of melt pool boundaries is revealed. These are associated with Fe depletion caused by an early planar growth front, and the evolution of these zones upon ageing is presented. With a high potential for industrial applications, the novel alloy with the two elements Zr and Fe exhibiting low solubility at equilibrium and diffusivity in the Al matrix permit to achieve high conductivity (27 MS/m) and yield strength (330MPa) after a simple direct ageing step at 400°C/4h.

Microstructure, mechanical properties and fracture mechanisms in a 7017 aluminium alloy tailored for powder bed fusion – laser beam

This study addressed a 7017 Al-alloy tailored for powder bed fusion – laser beam (PBF-LB) process. The alloy was prepared by mixing 3 wt% Zr and 0.5 wt% TiC powder to standard pre-alloyed 7017 grade aluminium powder. This made printing of the alloys possible avoiding solidification cracking in the bulk and achieving high relative density (99.8 %). Such advanced alloys have significantly higher Young’s modulus (>80 GPa) than conventional Al-alloys (70–75 GPa), thus making them attractive for applications requiring high stiffness. The resulting microstructure in as-printed condition was rich in particles originating from admixed powders and primary precipitates/inclusions originating from the PBF-LB process. After performing a T6-like heat treatment designed for the PBF-LB process, the microstructure changed: Zr-nanoparticles and Fe- or Mg/Zn- containing precipitates formed thus providing 75 % increase in yield strength (from 254 MPa to 444 MPa) at the cost of decreasing ductility (∼20 % to ∼9 %). In-situ tensile testing combined with SXCT, and ex-situ tensile testing combined with fracture analysis confirmed that the fracture initiation in both conditions is highly dependent on defects originated during printing. However, cracks are deflected from decohesion around Zr-containing inclusions/precipitates embedded in the Al-matrix. This deflection is seen to improve the ductility of the material.

A Brief Review on the Electrical Resistivity Of Aluminium Alloy and its Nanoparticles at Low Temperature

The objective of this review article is to study the resistivity of aluminium alloy at low temperatures. Various articles have been thoroughly studied for this review. Alloys that contain Al as dominant metal are termed as Al alloys. The first conventional Al alloy was prepared A6160 whose major constituents are Si and Mg. Al metal in its pure form has very high electrical conductivity but it is soft. Foils and conductor cables are made of Al. For advanced applications, Al is alloyed. The review has briefly explained the physical background of electrical resistivity and analysis of chosen material, aluminium alloy. Furthermore it has also discussed the resistivity of nanoparticles of Aluminium alloy.Keywords: Aluminium alloys, electrical resistivity, temperature, impurity.

Corrosion Analysis of Al-Ce-X Cast Alloys in Dilute Boric Acid and 3.5 Wt.% NaCl Solutions

New compositions of Al-Ce-X cast alloys have been developed to offer higher material performances than the conventional Al alloys for nuclear and other industrial applications. To assess the corrosion behavior of these new Al-Ce-X alloys, mass change measurements and electrochemical analysis were conducted using 0.23 wt.% boric acid solution, relevant to the water chemistry for the storage pool of spent nuclear fuels, and a 3.5 wt.% NaCl solution approximating sea water. Pre- and Post-corrosion Al alloy specimens were characterized by electron microscope systems including SEM, TEM and EDS. The initial electrochemical and mass change results suggest that Al-Ce-X alloys are resistant to corrosion in 0.23 wt.% boric acid but can be susceptible to corrosion in 3.5 wt.% NaCl solution. The initial characterization of post-corrosion samples indicated that one Al-Ce-X alloy type experiences uniform corrosion without any preferential or local attacks. Further corrosion analysis and characterization are underway for comprehensive understanding of corrosion phenomenon in these new alloys.

Design of heat-resistant Al–Mg –Zn–Cu–Ni quinary alloy: Controlling intermetallic phases and mechanical performance at elevated temperature

Owing to good formability, wrought Al alloys are used in a wide range of industries, including turbochargers in automobile engines. The development of Al alloys with increased high-temperature strength is necessary to improve the fuel efficiency of engines. In this study, a modified heat-resistant Al–Mg–Zn–Cu–Ni quinary alloy with superior high-temperature strength and creep rupture life at 200 °C (potential temperature in service for compressor radial impellers) was designed. The thermodynamic assessments provided a modified alloy composition of Al–5Mg–3.5Zn–2Cu–2Ni (at %) exhibiting α-Al phase in equilibrium with T-Al6Mg11Zn11 and Al3(Ni, Cu)2 phases at elevated temperatures. The experimental alloy showed granular T and Al3(Ni, Cu)2 phases often located on grain boundaries in the α-Al matrix, although the undissolved Al3Ni phase (formed in solidification) locally remained. Apart from the T phase, the η-Zn2Mg phase containing Cu element preferentially precipitated on grain boundaries. A large number of fine precipitates were dispersed homogeneously in the grain interior after the aging at 200 °C or 300 °C. Compared to the base alloy with a ternary composition of Al–5Mg–3.5Zn (at %) and conventional Al alloys, the designed quinary alloy (pre-aged at 200 °C for 10 h) showed a high strength at elevated temperatures above 200 °C. The creep-rupture life at 200 °C/105 MPa was remarkably extended to 665 h by the addition of Cu and Ni elements into the base ternary alloy. The rupture life was more than ten times longer than one (57 h) of the ternary alloys. The alloy modification based on the thermodynamic calculations provides an effective approach for designing lightweight Al alloys with superior high-temperature strength and creep rupture life.

Shock compression, melting and impedance mismatch studies in [formula omitted] based on first principles

Al-Li alloys have several advantages over conventional Al alloys on account of their properties such as low mass density and high strength. δ′−Al3Li phase is considered to be the most important strengthening phase in Al-Li alloys. In the present study, we predicted the shock induced compression of δ′−Al3Li for the first time. Our simulations indicated that shock induced melting was expected to occur in δ′−Al3Li at ∼80GPa. Hence, structural and mechanical stability of δ′−Al3Li were established up to 80GPa using ab-initio methods. First-principles calculations were done to obtain the parameters required for modelling equation-of-state of Al3Li. Further, impedance mismatch (IM) simulations were performed on bilayer targets (Al3Li-Au and Al-Au). It was observed from the simulations that use of Al3Li instead of Al led to ∼9% higher shock pressure amplification in Au. The ultimate tensile strength at which Al3Li ruptures was estimated and found to be ∼10.57GPa. It was also observed that, Al3Li becomes ductile at high pressures beyond 60GPa. Our study corroborates the use of Al-Li alloys which contain a huge volume fraction of Al3Li phase, as a structural material in place of Al in shock studies.

Industrially fabricated in-situ Al-AlN metal matrix composites (part B): The mechanical, creep, and thermal properties

The present study (part B) is a direct continuation of the leading study (part A), in which we had introduced extruded aluminum (Al) + 8.8 and 14.7 vol% aluminum nitride (AlN) metal matrix composites (MMC) manufactured at a cost-effective industrial scale and targeted for structural load-bearing applications with an expected service at elevated temperatures. In the leading study the processing, microstructure of nitrided and extruded Al-AlN MMC and the thermal stability of the extruded Al-AlN MMC as reflected in changes to their tensile mechanical properties induced by annealing up to 600 °C were elaborated. In the present ensuing study we discussed in details the mechanical, thermal and creep properties, active strengthening mechanisms, and microstructure-property relations of Al-AlN MMC annealed at 500 °C for 24 h, which were examined in a broad temperature range of 22–500 °C. In addition to increased Young`s modulus Al-AlN MMC showed high tensile strengths determined at 300 °C, which were superior to any conventional Al alloy, accompanied with reasonably high ductility. At the same time Al-AlN MMC preserved excellent creep performance, which was superior to the heat resistant reference alloys, reduced coefficient of thermal expansion and reasonable thermal conductivity. The results confirmed that reported thermally stable Al-AlN MMC may be considered a promising material with an appealing set of the properties directed for load-bearing structural applications with an expected service at elevated temperatures.

Investigation on mechanical properties of aluminium 8090 alloy through room temperature rolling

Al-Li alloys are attractive for military and aerospace applications because their properties are superior to those of conventional Al alloys. Their exceptional properties are attributed to the addition of Li into the Al matrix. To develop an improved approach in achieving an excellent combination of high strength and ductility, the solutionized Al-Cu-Li plates were subjected to rolling at room temperatures to a reduction of 60%, 75% and amp; 85%. Rolling at room temperature produces a high density of dislocations because of the suppression of dynamic recovery, such high density of T1 precipitates enable effective dislocation pinning, leading to an increase in strength and ductility. The tensile properties of the age hardening Al 8090 alloy subjected to room temperature rolling (RTR) were investigated. The rolled and aged alloys were analyzed by using TEM, Vickers hardness analysis and tensile test as per ASTM standards. The strength and ductility of Al 8090 alloy of rolled samples are compared to unrolled samples.

Tunable and Robust Nanostructuring for Multifunctional Metal Additively Manufactured Interfaces.

Novel processing phenomena coupled with various alloying materials used in metal additive manufacturing (AM) have opened opportunities for the development of previously unexplored micro-/nanostructures. A rationally devised structure nanofabrication strategy of AM surfaces that can tailor the interface morphology and chemistry has the potential for many applications. Here, through an understanding of grain formation mechanisms during AM, we develop a facile method for tuning micro-/nanostructures of one of the most used AM alloys and rationally optimize the morphology for applications requiring low surface adhesion. We demonstrate that optimized AM structures reduce the adhesion of impaling water droplets and significantly delay icing time. The structure can also be altered and optimized for antiflooding jumping-droplet condensation that exhibits significant enhancement in heat transfer performance in comparison to nanostructures formed on conventional Al alloys. In addition to demonstrating the potential of functionalized AM surfaces, this work also provides guidelines for surface-structuring optimization applicable to other AM metals.

Laser Powder Bed Fusion of an Al-Mg-Sc-Zr Alloy: Manufacturing, Peak Hardening Response and Thermal Stability at Peak Hardness

This study shows a rapid and systematic approach towards identifying full density and peak hardness for an Al-Mg-Sc-Zr alloy commonly known as Scalmalloy®. The alloy is tailored for the laser powder bed fusion process and has been shown to be printable with >99.8% relative density. The microstructure suggests Al grain refinement in melt pool boundaries, associated with formation of primary Al3(Sc,Zr) particles during solidification. Peak hardening response was identified by heat treatment tests at 573,598 and 623 K between 0 and 10 h. A peak hardness of 172 HV0.3 at 598 K for 4 h was identified. The mechanical properties were also tested with yield and ultimate strengths of 287 MPa and 364 MPa in as-printed and 468 MPa and 517 MPa in peak hardened conditions, respectively, which is consistent with the literature. Such an approach is considered apt when qualifying new materials in industrial laser powder bed fusion systems. The second part of the study discusses the thermal stability of such alloys post-peak-hardening. One set of samples was peak hardened at the conditions identified before and underwent secondary ageing at three different temperatures of 423,473 and 523 K between 0 and 120 h to understand thermal stability and benchmark against conventional Al alloys. The secondary heat treatments performed at lower temperatures revealed lower deterioration of hardness over ageing times as compared to the datasheets for conventional Al alloys and Scalmalloy®, thus suggesting that longer ageing times are needed.

Development and characterization of a metastable Al-Mn-Ce alloy produced by laser powder bed fusion

• Al 92 Mn 6 Ce 2 alloy was processed crack-free by laser powder bed fusion (LPBF). • The high cooling rate leads to a high amount and a strong refinement of metastable Al 20 Mn 2 Ce. • The compressive behavior overcomes as-cast Al 92 Mn 6 Ce 2 and many conventional Al alloys. Laser powder bed fusion (LPBF) can help to overcome two challenges occurring by casting of metastable Al alloys: (1) the high amount of casting defects and (2) the limited part size while maintaining rapid solidification of the whole cross-section. In this study, an Al 92 Mn 6 Ce 2 alloy was processed crack-free without baseplate heating by LPBF. The high cooling rate during fabrication has a significant impact on the microstructure, which was characterized by SEM, TEM and XRD. The processing through LPBF causes a high amount and a strong refinement of the intermetallic Al 20 Mn 2 Ce precipitates. This leads, compared to suction-cast specimens, to a higher hardness (180 HV 5) and a higher tolerable compressive stress (>1200 MPa) associated with a pronounced plasticity without failure up to a strain of 40%. The extraordinary mechanical properties of additively manufactured Al 92 Mn 6 Ce 2 can extend the possibilities of producing novel LPBF lightweight structures for potential applications under harsh conditions.

Enhanced thermal coarsening resistance in a nanostructured aluminum-cerium alloy produced by additive manufacturing

Decreasing microstructural length scales to the nanoscale is a proven way of increasing strength, but the intrinsic metastability of such structures typically makes them susceptible to thermally activated coarsening. Recent advances in additive manufacturing permit bulk-nanostructured materials to be produced through rapid solidification, but like other metastable materials the as-built structures typically coarsen rapidly with even modest thermal exposure. Here, selective laser melting is employed to produce an Al-Ce-based alloy with high mechanical strength arising from the as-built microstructure, which can be controlled by build conditions. In addition, the alloy exhibits extreme resistance to thermal coarsening up to 400 °C and superior strength retention compared to conventional Al alloys after extended thermal exposure. The near-zero solubility of Ce in Al and potent solid solution strengthening of Mg enable this behavior without requiring heat treatment. This result demonstrates that combining insoluble alloying elements with additive manufacturing is a viable method of producing exceptionally stable bulk nanoscale alloys.

Strength-conductivity synergy in cold-drawn reduced graphene oxide (RGO)-aluminum composite wires for electrical applications

We present a breakthrough of the strength-conductivity trade-off in cold wire drawn reduced graphene oxide (RGO)-aluminum (Al) composite. The composite was fabricated by a full glovebox powder metallurgy process, followed by hot rolling and wire drawing down to 0.5 mm wire diameter. Compared to the unreinforced Al fabricated by the same methodology, the incorporation of RGO in the 0.5 mm wire sample gave rise to approximately 20.7% improvement in mechanical strength, with only ~3.6% sacrifice in electrical conductivity. Furthermore, the 331.6 ± 6.8 MPa compressive strength and ~54.1%International Annealed Copper Standard (IACS) of the 0.5 mm wire RGO-Al composite exhibited a strength-conductivity combination comparable or even superior to conventional Al alloy conductors that go through complex thermal-mechanical treatments. Such a property synergy was interpreted by the ultra-fine Al grain structure and the elongated grain morphology rendered by the deformation processing steps, and an Orowan-typed strengthening mechanism owing to the homogenously dispersed natural amorphous alumina and RGO nanosheets in the composite.

Reversion of natural ageing and restoration of quick bake-hardening response in Al-Zn-Mg-Cu alloy

The high-strength Al-Zn-Mg-Cu alloy provides much better dent resistance and weight-reduction potential compared to the conventional Al alloys used for the automobile body panels. However, natural ageing (NA) significantly reduces the formability of Al-Zn-Mg-Cu alloy. The reversion of natural ageing has been systematically investigated by hardness test, tensile test, differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). Substantial reversion of natural ageing and thus hardness decrease occurs immediately upon thermal treatment at 120–210 °C in an Al-Zn-Mg-Cu alloy. Although the hardness of the most reverted state decreases with increasing temperature, the lowest hardness is still higher than the as-quenched state by 30HV. As revealed by the complementary DSC and TEM observations, this is ascribed to the synchronization of the dissolution and the re-precipitation of the solutes in the NA clusters during reversion ageing. Reversion at 180–210 °C for less than 30 s leads to a hardness decline of 40HV. The hardening kinetics during NA after reversion is slower than that during first-time NA due to the reduced vacancy concentration. Artificial ageing at 180 °C for 30 min after secondary NA of less than 24 h induces intensive precipitation of plate-like pre-η phases and a giant strength increase of 188–204 MPa. Potential use of high strength Al-Zn-Mg-Cu alloy in automobile body panels could be realized by appropriate reversion treatment improving the formability and the quick bake hardening response.

A review of the design of high-entropy aluminum alloys: a pathway for novel Al alloys

Aluminum (Al) alloys are of great importance and interest because of their extensive applications in various engineering fields. Lightweighting of our infrastructure has been a driver for more than the last two decades as our need to reduce carbon footprint on a global scale has become an inevitable reality. As a result, we have witnessed much progress in alloy development in Al alloys, especially with the advent of Integrated Computational Materials Engineering (ICME) and other computational tools. However, the limitations of the properties one may attain through alloy development to date have relied on the traditional solvent/solute model, where the matrix is Al with additions of elements (solute) to the matrix. Despite making much progress, we are still locked-in to the strength-ductility curve without any appreciable increase in modulus (stiffness) of the alloy. High Entropy Alloys (HEAs) provide a new paradigm as they differ from conventional alloys in entropy-based mixing logic of various elements, which is different from the solvent/solute model. HEAs offer the opportunity to move out of the strength-ductility curve as well as the opportunity to increase the alloy’s modulus. In this paper, we present a retrospective view of Al alloys, followed with an understanding of the principles of HEAs, and lastly, with the idea of applying high entropy concept to conventional Al alloys to develop a novel Al alloy category, which we have coined HEAl. Preliminary results with a commentary on potential future opportunities are also given.

Experimental study on the cutting responses and surface integrity of side milled in situ TiB2/Al composites

Research on the machinability of particle-reinforced Al matrix composites (PRAMCs) is significant to their industrial applications. In the present article, the side milling process of two in situ TiB2/Al composites (in situ 6% TiB2/2024 Al composite and in situ 4% TiB2/7075 Al composite) and the corresponding Al alloys (2024 Al alloy and 7075 Al alloy) were investigated. Cutting responses, including milling force and temperature, were monitored and analyzed. Surface integrity, including roughness, topology, morphology, microstructure, and residual stress of the machined samples, was comprehensively characterized and analyzed. Results showed that, by adjusting the process parameters in appropriate ranges, the milling force and temperature of in situ TiB2/Al composites can be controlled at almost the same level of those of conventional Al alloys. Besides, in situ TiB2/Al composites showed better surface finish and larger process window than conventional Al alloys, which can be helpful for the side milling of precision parts, especially for ensuring the high surface quality of the workpiece without special setting of the process parameters. It is worthy to be noticed that side milling can make the TiB2 particles distribute more evenly on the sample surface, which can be beneficial to the comprehensive surface mechanical properties of the in situ TiB2/Al composites.

Review: Synthesis and characterization of silicon nitride and graphite reinforced aluminium hybrid metal matrix composites

Abstract In the last decade, as demand for high quality materials are increased, the development of lightweight aluminum (Al) also increased especially in aerospace and automotive industries. It has been well known that Al based metal matrix composites (MMCs) offers a very low thermal expansion coefficient, high specific strengths, wear and heat resistance as compared to conventional Al alloys. In order to combine all these properties, MMCs have become a very attractive method for various industrial applications. The interest in Silicon Nitride (Si3N4) and Graphene as reinforcements for aluminum (Al7475) has been growing considerably. Efforts have been largely focused on investigating their contribution to the enhancement of the mechanical performance of the composites. In this present research paper emphasis, the effect of Silicon Nitride (Si3N4) and Graphene content on the Physical properties of the composites like Wear Test, Hardness Test & Microstructure Testing was investigated.