In recent years, much progress has been made in the studies of nanostructured Al alloys for advanced structural and functional use associated both with the development of novel routes for the ...fabrication of bulk nanostructured materials using severe plastic deformation (SPD) techniques and with investigation of fundamental mechanisms leading to improved properties. This review paper discusses new concepts and principles in application of SPD processing to fabricate bulk nanostructured Al alloys with advanced properties. Special emphasis is placed on the relationship between microstructural features, mechanical, chemical, and physical properties, as well as the innovation potential of the SPD-produced nanostructured Al alloys.
Wrought aluminium alloys popular for automotive and aerospace applications are susceptible to solidification cracking when fabricated via laser powder bed fusion (LPBF). Another long-standing and ...common issue for these alloys is microstructure coarsening and corresponding strength loss caused by elevated temperature exposure. To tackle these challenges, this study designs and develops a class of 1–4 wt% Ce modified Al6061 alloys. The best alloy, with 3 wt% Ce, achieves crack-free fabrication via LPBF due to a reduction in the solidification temperature range and a new solidification pathway that achieved 0.9 solid mass fraction at just 14 °C below the solidification onset. Furthermore, a fine microstructure consisting of coarsening-resistant τ1-CeAlSi eutectic forms, and after hot isostatic pressing, the tensile strength and elongation of the 3 wt% Ce alloy can reach 153 ± 6 MPa and 18.3% at room temperature and 89 ± 6 MPa and 32.5% at 200 °C, respectively. The observed ductility is attributed to nanoscale dispersion of discrete, coarsening resistant τ1-CeAlSi particles within grains and to the presence of large columnar α-Al grains. Meanwhile, solidification cracking was inhibited by continuous grain boundary τ1-CeAlSi eutectic accumulation, which converted to discrete nanoscale τ1-CeAlSi after hot isostatic pressing. This research uncovers a simple and effective approach of designing Al-alloys for LPBF with great potential for both room temperature and high temperature applications in automotive and aerospace industries.
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In the aviation industry, fretting fatigue represents a significantly hazardous form of fatigue failure, thus warranting substantial research attention. A key area of focus lies in enhancing the ...fretting fatigue resistance of aluminium alloys. This study investigates the feasibility of using Friction Stir Processing (FSP) to enhance fretting fatigue lifetime. After FSP, large-size inclusions in the Base Material (BM) are shattered, clustered inclusions are dispersed, and the preferred orientation of inclusions is disrupted. Consequently, areas of stress concentration, damage concentration and merging of hazardous zones become less, and the peak values of stress, stress triaxiality, and damage are decreased with 6–10 %. Compared to BM, the results show that the fretting fatigue lifetime of Friction Stir Processed (FSPed) material is increased by 50.1 %. Hence, FSP could emerges as a highly promising surface treatment technique for enhancing fretting fatigue performance.
► The hot deformation behaviour of the Al 2024 alloy was analyzed by torsion testing, constitutive equations and processing maps. ► EBSD was employed to characterize the microstructure and its ...correlation with processing maps. ► A forming temperature range of 360–410°C and strain rates of 2.1–4.5s−1 is recommended. ► Extended dynamic recovery (DRV) under the most favourable conditions leads to uniform and fine grain size. ► The behaviour of precipitates at processing temperature determines the mechanical properties.
The forming behaviour of an Al–Cu–Mg alloy (Al 2024-T351) has been studied by processing maps and microstructural characterization. Torsion tests were conducted in the range 278–467°C, between 2.1 and 25.6s−1. Stress–strain curves obtained from the experiment data were fitted using the Garofalo equation to obtain the constitutive parameters, obtaining a stress exponent of 6.1 and an activation energy of 180kJ/mol. Electron backscatter diffraction (EBSD) was employed to characterize the microtexture and microstructure, before and after torsion testing, to evaluate the microstructural changes and instability phenomena. A peak ductility of the Al 2024 alloy was found at about 400°C at all strain rates considered. According to the processing maps and microstructure observation, the optimum hot deformation condition for the Al 2024 alloy is in the range 360–410°C and 2.1–4.5s−1. Under these favourable conditions a uniform and fine grain size is obtained by extended dynamic recovery (DRV), which leads to the formation of subgrain boundaries that progressively transform at large strains into new high angle grain boundaries.
► The Sc effect on the microstructure and ageing behaviour of Al–Sc alloys is studied. ► Cast into copper mould allows the elimination of solution heat treatment. ► Directly aged as cast alloys ...exhibits higher hardness and precipitation kinetics. ► Sc addition and optimised ageing result in an increase in Al–Sc mechanical properties.
The grain refinement effect and the ageing behaviour of Al–0.5wt.% Sc, Al–0.7wt.% Sc, and Al–1wt.% Sc alloys are studied on the basis of optic microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) observations and hardness measurements. In Al–Sc alloys the higher grain refinement is observed for Sc contents greater than 0.5wt.% accompanied by a notorious morphology modification, from coarse columnar grains to a fine perfect equiaxed structure. The as cast structures are characterised by a rich supersaturated solid solution in Sc, that promotes a great age hardening response at 250°C and 300°C. The age hardening curves also demonstrate a low overageing kinetics for all the alloys. Although the higher Sc content in solid solution for the alloys with 0.7 and 1wt.% Sc, the age hardening response of all the Al–Sc alloys remains similar. The direct age hardening response of the as cast Al–0.5wt.% Sc is shown to be greater than the solutionised and age hardened alloy.
Selective laser melting of aluminium components Louvis, Eleftherios; Fox, Peter; Sutcliffe, Christopher J.
Journal of materials processing technology,
02/2011, Letnik:
211, Številka:
2
Journal Article
Recenzirano
Previous work has shown that the processing of aluminium alloys by selective laser melting (SLM) is difficult, with reasonable components only being produced with high laser powers (minimum 150
W) ...and slow laser scanning speeds. The high laser power is a significant problem as it is higher than that used in many SLM machines. Also, the combination of high power and low speed creates a large melt pool that is difficult to control, leading to balling of the melt and possible damage to the powder distribution system. Even when processing is carried out successfully, the high power and slow scan speed significantly increase build time and the manufacturing costs.
This paper considers the changes that can be made to the SLM process so as to reduce the laser power required and increase the laser scanning rates, while still producing components with a high relative density. It also considers why aluminium and its alloys are much more difficult to process than stainless steels and commercially pure titanium. Two MCP Realizer machines were used to process 6061 and AlSi12 alloys, one processing at 50
W and the other 100
W laser power. Even with an optimum combination of process parameters a maximum relative density of only 89.5% was possible (achieved with 100
W). The major confounding factor for processing aluminium and its alloys was found to be oxidation due to the presence of oxygen within the build chamber. This formed thin oxide films on both the solid and molten materials. It was observed that the oxide on the top of the melt pool vaporised under the laser creating a fume of oxide particles, while melt pool stirring, probably due to Marangoni forces, tended to break the oxide at the base of the melt pool allowing fusion to the underlying tracks. However, the oxides at the sides of the melt pool remained intact creating regions of weakness and porosity, as the melt pool failed to wet the surrounding material. Therefore, if 100% dense aluminium components are to be produced by SLM, using low laser powers, methods need to be developed that can either disrupt these oxide films or avoid their formation.
Pronounced crystallographic texture, characteristic for the parts manufactured by selective laser melting, is eliminated upon addition of TiB2 microparticles to Al-12Si powder. Due to the wetting of ...TiB2 ceramic by Al-12Si melt and a high inoculation efficiency, a homogeneous microstructure consisting of fine equiaxed grains with random crystallographic orientation is formed by SLM processing of the Al-12Si/TiB2 powder mixture. The Al-12Si/TiB2 samples exhibit enhanced yield strength and microhardness, compared to the TiB2-free Al-12Si samples produced at the same SLM conditions.
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•Good wettability and high work of adhesion for liquid Al-12Si and TiB2 ceramic.•TiB2 efficient in texture elimination and grain refinement by SLM of Al-12Si.•Enhanced mechanical properties for Al-12Si/TiB2 samples fabricated by SLM.
Voids can be detrimental to the mechanical and electrical properties of materials but may also find applications in catalysis and plasmonics. Key to the performance of materials containing voids are ...the sizes and morphologies of the voids, which can be tuned by heat treatment. The present work investigates the morphological evolution of voids, with solute segregation at their surfaces, in an aluminium‑copper‑tin alloy during in situ heating in a transmission electron microscope (TEM). These voids exhibited complex morphological changes that included growth or shrinkage, in contrast to voids in pure Al, which all shrank and disappeared (as reported in an earlier study). Without electron irradiation, the voids never grew. Nearly one fourth of the voids grew under certain heating and electron irradiation conditions, showing distinct growth stages. Growth and shrinkage of the voids both occurred primarily along the surface of the Sn particles to which they were attached. The voids exhibited faceting as they grew and gained morphological isotropy while they shrank. The growth and shrinkage fronts were both found to be primarily the curved surfaces and not the facets at the void surfaces. Growth followed by shrinkage led to a well-defined rounded triangular shape, in projection, with smooth boundaries. This work is, to the best of our knowledge, the first to characterise the growth of nanoscale voids in aluminium using in situ heating TEM. The dual effect of heating and electron irradiation could be utilised to switch the voids between growth and shrinkage to manipulate the void size and shape. This work provides useful insights into tuning void morphologies in the development of advanced materials such as for applications in engineering, catalysis and plasmonics.
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•In situ heating TEM revealed void growth stages which are more complex than a model simply controlled by interfacial energy.•During in situ heating TEM, electron irradiation is as crucial as heating to the void growth.•The dual effects of heating and electron irradiation could be utilised to manipulate the void size and shape.
Aluminium alloys are crucial in lightweighting equipment. However, their limited wear resistance hinders their further utilization. Herein, a gradient nanostructure layer incorporating α-Al2O3 ...particles is successfully fabricated on aluminium alloy 2024 using a novel method called strengthening grinding treatment (SGT). The tribological properties were investigated by a ball-on-disc tribometer. The results show that SGT effectively enhances the anti-wear performance. Compared to the untreated sample, the average friction coefficient and the wear rate of the SGT-treated sample decreased by 34.7 % and 90.1 %, respectively. The wear surface analysis demonstrates that the presence of α-Al2O3 in the gradient nanostructure effectively restricts shear deformation and crack generation. Additionally, the formation of a wear-resistant tribofilm composed of 'glaze' during friction contributes to further wear reduction.
Room temperature solute clustering in aluminium alloys, or natural ageing, despite its industrial relevance, is still subject to debate, mostly due to its experimentally challenging nature. To better ...understand the complex multi-constituents’ interactions at play, we have studied ternary and quaternary subsystems based on the Al-Cu alloys, namely Al-Cu-Mg, Al-Cu-Li and Al-Cu-Li-Mg. We used a recently introduced correlative technique using small-angle neutrons and X-ray scattering (SANS and SAXS) to extract the chemically resolved kinetics of room temperature clustering in these alloys, which we completed with DSC and micro-hardness measurements. The comparison of the clustering behaviours of each subsystem allowed us to highlight the paramount role of Mg as a trigger for diffusion and clustering. Indeed, while a strong natural ageing was observed in the Al-Cu-Mg alloy, virtually none was shown for Al-Cu-Li. A very slight addition of Mg (0.4%) to this system, however, drastically changed the situation to a rapid formation of essentially Cu-rich hardening clusters, Mg only joining them later in the reaction. This diffusion enabling effect of Mg is discussed in terms of diffusion mechanism and complex interactions with the quenched-in vacancies.
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