Nanostructured Aluminum Alloy Research Articles

Comparative analysis of experimental techniques for microstructural characterization of novel nanostructured aluminium alloys

Precipitation holds a pivotal role in comprehending the intrinsic behavior of materials. In the design of nanostructured metallic alloys, precipitates have found to increase the alloys' stability and response under extreme environmental conditions. Studies on precipitation often rely on conventional and ex situ electron-microscopy methods, but a systematic investigation that compares different sample conditions during heat treatment and its microstructural implications are rarely available. In this context, we employed a novel ultrafine-grained AlMgZnCuAg crossover alloy to compare three distinct conditions for investigating the precipitation sequence: (i) ex situ transmission electron microscopy (TEM) from bulk heating, (ii) ex situ TEM from TEM foil heating, and (iii) in situ TEM with microelectromechanical-system (MEMS) heating. Although the heat treatment procedure was consistent across all cases studied, the application of these three different experimental conditions in the same alloy system resulted in significant and non-negligible differences in the final precipitation behavior. Ultimately, it resulted in observable microstructural variations and precipitates with distinctively different shape and sizes and, as a result, we outline herein the major similarities and differences among these techniques to achieve comparable results. This knowledge will help to compare and assess results of precipitation sequences obtained in different conditions.

Achieving strength-ductility synergy in Al-4.5 wt%Cu binary alloy through semisolid isothermal treatment coupled with ECAP

Bulk nanostructured (NS) aluminum alloys typically have high strength but with extremely limited ductility. An advanced two-step thermomechanical processing, i.e. semisolid isothermal treatment coupled with equal-channel angular pressing (ECAP), was adopted to achieve high strength (413±2.5 MPa) and high elongation (12.0±0.6 %) in bulk NS Al-4.5 wt%Cu binary alloy. The broken nanoscale Al2Cu particles (∼50–80 nm) from lamellar eutectic, dynamic precipitations Al2Cu (∼30–60 nm), refined grains, and high-density dislocations are believed to be key contributors for the high strength. The bimodal grain structure, which caused a well-balanced work hardening and a good deformation compatibility, is critical for the enhanced strength-ductility synergy. This work demonstrates a new approach for improving strength-ductility synergy in interdendritic-eutectic type aluminum alloys.

Enhancing Fuel Efficiency of Internal Combustion Engine through the Application of Nanostructured Aluminium Alloy in Pistons

‌The automobile and motorsport industires are under immense pressure due to emission laws to reduce fuel consumption and alleviate the effects of global warming. This experimental study compared the performance of internal combustion engine pistons made of a newly developed nanostructured aluminium alloy (RSA-612) and conventional aluminium alloy 2618. The new alloy is expected to reduce piston mass which will reduce piston assembly frictional losses and lead to reduced fuel consumption. The new alloy has lower density and higher strength at elevated temperatures than conventional aluminum alloys, and the final machined piston was 13.5% lighter than the original piston. The limited engine testing carried out in this study showed that the new piston produced enhanced performance in certain engine operating conditions, whilst performing similarly or slightly worse in others. Further testing with the new piston is advised to assess engine performance across wider engine running envelope.

Examination of inverse Hall-Petch relation in nanostructured aluminum alloys by ultra-severe plastic deformation

To have an insight into the occurrence of inverse Hall-Petch relationship in ultrafine-grained (UFG) aluminum alloys produced by severe plastic deformation (SPD), ultra-SPD (i.e. inducing several ten thousand shear strains via high-pressure torsion, HPT) followed by aging is applied to an Al-La-Ce alloy. Average nanograin sizes of 40 and 80 nm are successfully achieved together with strain-induced Lomer-Cottrell dislocation lock formation and aging-induced semi-coherent Al11(La,Ce)3 precipitation. Analysis of hardening mechanisms in this alloy compared to SPD-processed pure aluminum with micrometer grain sizes, SPD-processed Al-based alloys with submicrometer grain sizes and ultra-SPD-processed Al-Ca alloy with nanograin sizes reveals the presence of two breaks in the Hall-Petch relationship. First, a positive up-break appears when the grain sizes decrease from micrometer to submicrometer which is due to extra hardening by solute-dislocation interactions. Second, a negative down-break and softening occur by decreasing the grain sizes from submicrometer to nanometer which is caused by weakening the dislocation hardening mechanism with minor contribution of the inverse Hall-Petch mechanism. Detailed analyses confirm that nanograin formation is not necessarily a solution for extra hardening of Al-based alloys and other accompanying strategies such as grain-boundary segregation and precipitation are required to overcome such a down-break and softening.

Inhibition Effectiveness of Laser-Cleaned Nanostructured Aluminum Alloys to Sulfate-reducing Bacteria Based on Superwetting and Ultraslippery Surfaces.

This paper is a continued study on laser cleaning removal of marine microbiofouling from Al alloy surfaces. According to our previous study, it is noted that the antifouling functions of the generated laser-cleaned metallic surfaces must be highlighted. In this work, the inhibition effectiveness of the laser-cleaned Al alloy surfaces was evaluated using a type of vital marine microorganism, sulfate-reducing bacteria (SRB) Desulfovibrio desulfuricans subsp. desulfuricans, in a dynamic bacterial solution. Before the immersion tests, the laser-cleaned surfaces with nanostructures were chemically processed into superhydrophilic, superhydrophobic, and ultraslippery surfaces. SRB attachment behaviors as well as inhibition mechanisms of the three surfaces to the SRB settlement were characterized and revealed. The SRB adhering to the above surfaces presented three different morphologies, i.e., broken, dented, and plump cells. Superhydrophilic surfaces unexpectedly showed a not inferior antibacterial ability. A piercing effect of the nanostructures caused nontoxic mechanical damage to the cell membranes. The antiadhesion property of superhydrophobic solid-air hybrid surfaces was unreliable due to the loss of air bubbles. The morphology of the last surviving SRB cells left on the ultraslippery surfaces was basically plump. The stable repellent function of the surfaces was responsible for the vigorous prevention of the adhesion of the SRB. The research results offer an insight into the antibacterial/antiadhesion properties of the laser-cleaned surfaces and a practical value for the periodic service of marine high-end equipment.

Microstructural Changes with Annealing of a Nanostructured Al Alloy Severely Plastic Deformed by Four-Layer Stack Accumulative Roll-Bonding Process.

Microstructural changes with annealing of a nanostructured complex aluminum alloy fabricated by 3 cycles of four-layer stack ARB process using different Al alloys were investigated in detail. The four-layer stack ARB process using AA1050, AA5052 and AA6061 alloy sheets was performed up to 3 cycles without a lubricant at room temperature. The sample fabricated by the ARB is a multi-layer aluminum alloy sheet in which the AA1050, AA5052 and AA6061 aluminum alloys are alternately stacked to each other. The layer thickness of each alloy became thinner and elongated to the rolling direction with the number of ARB cycles. The grain size decreased with increasing of the number of ARB cycles, and became about 160 nm in thickness after 3 cycles. The complex Al alloy still showed ultrafine grained microstructure to annealing temperature of 300 °C, but it had a heterogeneous structure containing both the ultrafine grains and the coarse grains due to an occurrence of discontinuous recrystallization after 350 °C.

Hierarchical nanostructured aluminum alloy with ultrahigh strength and large plasticity

High strength and high ductility are often mutually exclusive properties for structural metallic materials. This is particularly important for aluminum (Al)-based alloys which are widely commercially employed. Here, we introduce a hierarchical nanostructured Al alloy with a structure of Al nanograins surrounded by nano-sized metallic glass (MG) shells. It achieves an ultrahigh yield strength of 1.2 GPa in tension (1.7 GPa in compression) along with 15% plasticity in tension (over 70% in compression). The nano-sized MG phase facilitates such ultrahigh strength by impeding dislocation gliding from one nanograin to another, while continuous generation-movement-annihilation of dislocations in the Al nanograins and the flow behavior of the nano-sized MG phase result in increased plasticity. This plastic deformation mechanism is also an efficient way to decrease grain size to sub-10 nm size for low melting temperature metals like Al, making this structural design one solution to the strength-plasticity trade-off.

Tribological and mechanical behaviours of nanostructured aluminium alloys and nanocomposites at elevated temperatures: A short review

Aluminium alloys demonstrate exceptional properties such as high strength-weight ratio and corrosion resistance are used for general engineering applications, automobile, automotives and in aerospace industries. However, they suffer some limitations as wear and creep at high temperatures. With the trending developments from nanometallurgy, diverse nano-particle compounds of mono and heterogeneous compositions have been used in reinforcing aluminium and its alloys as widely reported in the public domains. This paper reviews some of the vast literature on the enhancement of nanostructured aluminium alloys and reinforced aluminium nanocomposites. Importance is laid on the tribological and mechanical behaviours of the manufactured composites and nano-composites with respect to their production methods and applications at elevated (high) and cryogenic (low) temperatures. Keywords— Tribology; mechanical behaviours; nanostructure; aluminium alloys; nano-composites; elevated temperatures

The effect of ARB process on corrosion behavior of nanostructured aluminum alloys in Na2HPO4·12H2O and Zn(NO3)2·6H2O PCMs

Phase change materials (PCMs), have high thermal energy storage due to hidden heat. One of the PCMs is hydrate salts. The insufficient long term stability of the storage materials, as containers, are the main concern in the energy storage systems which were investigated in this study. In this order, various common metals (Fine-grained Al1100 and Al6061 alloys by six cycles of accumulative roll bonding (ARB)) process were selected, and their corrosion resistance in contact with two different hydrate salts of (Na2HPO4·12H2O and Zn(NO3)2·6H2O) were tested. The immersion test method was utilized. In this way, samples were placed in the test tubes containing molten hydrate salts into a thermo-static water bath in three different periods of six, twelve and eighteen days at the temperature range of 55 to 60 °C. After each period, the sample weight loss rate was measured, and then the corrosion rate was calculated. The corrosion rate of ARBed Al 1100 and ARBed Al 6061 alloys in the Na2HPO4·12H2O at the end of eighteen days were 103.07 and 78.82 mpy, respectively. Furthermore, the corrosion rate of ARBed Al 1100 and ARBed Al6061 alloys in the Zn(NO3)2·6H2O was reported 88.67 and 68.71 mpy, respectively. The results indicated that the corrosion rate for Al1100 alloy is less and more than Al6061 alloy in the molten Na2HPO4·12H2O and molten AZn(NO3) 2·6H2O, respectively.

Removing the oxide layer in a nanostructured aluminum alloy by local shear deformation between nanoscale phases

The presence of oxide layers on the surface of the particles hinder solid-state sintering and significantly deteriorate the mechanical properties of high strength Al-based alloys fabricated by powder metallurgy via sintering, hot pressing, spark plasma sintering, etc. Here we report a synthesis route, which can completely break down the oxide layer in a nanostructured Al-based alloy. The nanostructured aluminum alloy was fabricated by hot pressing of nanostructured powders, which were synthesized by crystallization of amorphous powders. The nanostructured powders contain a high volume fraction of intermetallics embedded in a nanocrystalline Al-matrix. It was found that the oxide layers were broken down as a result of the local shear deformation between the nanoscale intermetallic phases and nanocrystalline fccAl. Consequently, the consolidated powders achieve an oxide layer-free bonding, which avoids crack initiation and propagation along the boundary between the initial powder particles, thus helping to obtain high-performance properties.

Advanced composite alloys for constructional parts of robots

In recent years all over the world special attention has been paid to the development and implementation of nanostructured materials possessing unique properties and opening fascinating prospects for the development of technical progress in various fields of human activities. A special place can be given to the development of service robots, the market of which is actively developing. There is problem associated mainly with the lack of heat-strengthened alloys which consists in low thermal stability of the alloy properties under the conditions of elevated variable temperatures and loads. The article presents studies to assess the effect of composition, the amounts of refractory nanoscale particles and methods for their introduction into the melt on the structure and properties in nanostructured composite aluminum alloys. The powders of metals, alloys, as well as silicon carbide and aluminum oxide were used to produce the nanostructured powder composite materials. As a result of the research, NPCM compositions containing micro-size particles of transition metals that are carriers of nanosized reinforcing particles and initiators of the formation of an intermetallide of endogenous origin in a melt.

Transition from poor ductility to room-temperature superplasticity in a nanostructured aluminum alloy

Recent developments of nanostructured materials with grain sizes in the nanometer to submicrometer range have provided ground for numerous functional properties and new applications. However, in terms of mechanical properties, bulk nanostructured materials typically show poor ductility despite their high strength, which limits their use for structural applications. The present article shows that the poor ductility of nanostructured alloys can be changed to room-temperature superplastisity by a transition in the deformation mechanism from dislocation activity to grain-boundary sliding. We report the first observation of room-temperature superplasticity (over 400% tensile elongations) in a nanostructured Al alloy by enhanced grain-boundary sliding. The room-temperature grain-boundary sliding and superplasticity was realized by engineering the Zn segregation along the Al/Al boundaries through severe plastic deformation. This work introduces a new boundary-based strategy to improve the mechanical properties of nanostructured materials for structural applications, where high deformability is a requirement.

Effects of Degassing on the Microstructure, Chemistry, and Estimated Mechanical Properties of a Cryomilled Al-Mg Alloy

Nanostructured aluminum alloys produced through cryomilling have generated interest due to their potential to create consolidated parts with high strength and low density. Degassing prior to consolidation minimizes adsorbed and absorbed volatiles, but is accompanied by microstructural changes such as grain growth, dislocation annihilation, and formation of dispersoids. These changes can influence the mechanical behavior of consolidated components. Cryomilled AA5083 was degassed at temperatures from 473 K to 773 K (200 °C to 500 °C) with a vacuum at or below 2.7 × 10−3 Pa. Grain size in the as-cryomilled powder (ranging from 21 to 34 nm) increased with higher degassing temperature and reached a maximum size of up to 70 to 80 nm. The dislocation density of 1.11 × 1015 m−2 in as-cryomilled powder decreased to 1.56 × 1014 m−2 for powder degassed at 773 K (500 °C). The Al6(MnFeCr) dispersoid formed when powders were degassed at or above 573 K (300 °C). Oxygen and nitrogen concentrations were unaffected by degassing; however, hydrogen concentration decreased with increasing degassing temperature to a minimum of 45 ± 3.16 ppm. Evolutions in composition and microstructure in cryomilled AA5083 were correlated to the strengthening mechanisms of grain size reduction (i.e., Hall–Petch), dislocation forest, and Orowan. However, strengthening by grain size reduction was the dominant strengthening mechanism.

Investigation into the corrosion rate and features of the samples made of nanostructured aluminum alloy in the H2S-containing medium

The corrosion rate was determined and corrosion damage features of the samples made of AK4-1 aluminum alloy were investigated in the NACE solution containing hydrogen sulfide (H2S). The alloy was investigated in the ultra-fine-grain state compared with the coarse-grain state formed after standard treatment T6 (quenching + ageing). The alloy was nanostructured by equichannel angular pressing (ECAP). It is shown that the alloy corrosion rate after ECAP is higher than after T6 treatment by a factor of 1.9. Herewith, the total corrosion takes place in alloy after ECAP, while pitting corrosion is also observed after T6 treatment in addition to the total corrosion. The corrosion effect strongly affects surface-roughness parameters of the samples made of AK4-1 alloy after ECAP compared with the samples after T6 treatment.

Hybrid nanostructured aluminum alloy with super-high strength

Methods to strengthen aluminum alloys have been employed since the discovery of the age-hardening phenomenon in 1901. The upper strength limit of bulk Al alloys is ~0.7 GPa by conventional precipitation strengthening and increases to >1 GPa through grain refinement and amorphization. Here we report a bulk hybrid nanostructured Al alloy with high strength at both room temperature and elevated temperatures. In addition, based on high-resolution transmission electron microscopic observations and theoretical analysis, we attribute the strengthening mechanism to the composite effect of the high-strength nanocrystalline fcc-Al and nano-sized intermetallics as well as to the confinement effect between these nano phases. We also report the plastic deformation of nano-sized intermetallics and the occurrence of a high density of stacking faults and twins in fcc-Al after low-strain-rate deformation at room and high temperatures. Our findings may be beneficial for designing high-strength materials for advanced structural applications. An international team of scientists create an aluminum alloy that is twice as strong as those made by conventional techniques. Zhi Wang from IFW Dresden in Germany and Tohoku University in Japan and co-workers from China, Germany, Japan and Austria have developed a technique that allows the microstructure of aluminum alloys to be carefully controlled, enabling them to create hybrid structures consisting of nanoscale intermetallic compounds in an aluminum matrix. Previous attempts to create strong alloys included making an aluminum-based material that is non-crystalline, like glass, or one that is made up of crystalline nanograins. But these approaches lead to materials that are unsuitable for use at high temperatures. In contrast, the aluminum alloy created by the researchers exhibits high strength at both ambient and elevated temperatures. We report a bulk hybrid nanostructured Al alloy with super-high strength at both room and elevated temperatures. The strengthening mechanisms were clearly elucidated, which are mainly attributed to the composite structure and confinement effect between the nano phases. The confining effect can effectively suppress the premature brittle fracture of the nano-intermetallic phases. The microstructural strategy and strengthening mechanisms in this work may be beneficial for the scientific community in understanding and designing high-strength materials.

Comparative Studies of Nanostructured Aluminum Alloys by Destructive and Nondestructive Testing

This work provides a comparative study of the mechanical properties of composite materials based on aluminum reinforced with carbon nanostructures. The study involved the tensile strength testing, as well as sclerometry and indentation in the submicron range. We determined the correlation of the values obtained for yield strength and hardness, and the tensile strength and morphology of the residual scratches.

Tailoring a gradient nanostructured age-hardened aluminum alloy using high-gradient strain and strain rate

Microstructural evolution of Al2024 alloy, consisting of precipitates, subjected to surface mechanical grinding treatment (SMGT) was investigated to reveal the role of strain and strain rate in structural refinement. Following SMGT, a gradient nanostructure was formed on the coarse-grained substrate, with a significant increase in nanohardness to over 1 GPa at the top surface. At low strains, the presence of particles and increasing strain rate stimulated the rapid transformation of dislocation configurations. However, at larger strains, increasing strain rate effectively stabilized the fine nanoscale structure. Strain gradient from the deformed layers and near the particles significantly promoted the development of microstructure by increasing the boundary misorientations, which was more significant at high strain rates. In particular, at very high rates and large strain gradients, extreme grain sizes may be induced. The presence of minority grains with size below 10 nm in the top 20-μm layers revealed that dislocation processes still operated at sub-nanoscale level. The dislocation-governed ductility was expected to be improved in the nanostructured materials.

Stress-enhanced grain growth in a nanostructured aluminium alloy during spark plasma sintering

In this study, we report on the influence of high pressure on the microstructure evolution of cryomilled nanostructured Al alloy powders during spark plasma sintering (SPS). Our experimental results suggest that the particular mechanism that governs grain growth during SPS depends on the magnitude of the applied pressure. In the case of material consolidated at a high pressure (e.g. 500 MPa), grain coarsening occurs via a combination of thermally activated grain boundary (GB) migration, stress-coupled GB migration and grain rotation-induced grain coalescence. In contrast, in the case of the material consolidated at a low pressure (50 MPa), grain growth occurs primarily via thermally activated GB migration.

Microstructural Analysis of Nanostructured Aluminum Alloy Strips Created from Machining Based Deformation Process

Aim of present research endeavour is to fabricate nanostructured strips of aluminium alloy by a machining based deformation process. Aluminium 6061 was used as a test material. Furthermore, X-Ray diffraction (XRD) is used for deformation analysis of strips to check the level of deformation along their thickness. Microhardness testing was done using Vickers microhardness testing machine. Microstructure characterization of bulk aluminium and chips (as strips) was done by electron back scatter diffraction (EBSD). For in-depth deformation analysis thickness of strips was reduced in steps up to 100μm by abrasive papers. After each step of reducing thickness of strips by 100μm, X- ray scan and microhardness testing of strips were performed. The results show that microstrain in strips was increased and crystallite size was decreased. Moreover, hardness of the strips was ∼ 40-44% more than the bulk material. Higher hardness in strips may be attributed to their ultrafine microstructure resulted from high deformation observed in strips. Furthermore, variation in deformation level along the thickness of sheets was also observed.

Finite element modelling and experimental analysis of the processing conditions for obtaining straight blades by isothermal forging of a nanostructured aluminium-magnesium alloy

In this present study, both the design and the optimal manufacturing conditions for processing a straight blade by isothermal forging are shown. The starting material has been previously deformed by a severe plastic deformation (SPD) process known as equal channel angular extrusion (ECAE). As is well-known, the ECAE process is a technology which allows us to obtain materials with sub-micrometric grain size. These nanostructured materials can be employed afterwards as initial materials for other manufacturing processes. The use of these ultra fine grain sized materials (UFG) provides improved mechanical properties such as: greater hardness and mechanical strength, among others. In this present study, FEM simulations of the isothermal forging of an AA5083 previously deformed by ECAE will be carried out. The total equivalent plastic strain, the damage and the forces required to carry out the isothermal forging of this nanostructured aluminium alloy will be determined.