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Reinforcement of aluminum and aluminum alloys with graphene has been intensively practiced by researchers in the past dozen years. The role of Al4C3, which could be produced unintentionally or purposefully during the composite production, was controversial until it was found that nano-sized carbides were beneficial for strengthening the composites. aluminum-graphene-nano-sized Al4C3 composites were produced by us using the powder metallurgical method and subsequent annealing. The microstructure was investigated using light microscopy (LM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and high resolution transmission electron microscopy HRTEM. Nano-sized carbides were found at the interface aluminum-graphene. The formation of a chemical bond between aluminum and graphene during annealing was proved. Lower values of the microhardness and strength characteristics of the composites after extrusion and subsequent annealing during which nano-sized carbides are formed were found in comparison with those obtained after extrusion. It could be supposed that the annealing processes contribute more to the reduction in microhardness and strength characteristics than nano-sized carbides contribute to its increase. The presence of a strong chemical bond between the graphene and the aluminum is manifested in the failure pattern, which is characterized by graphene nano-platelets and nano-sized carbides fracture and semi-pulled out or semi-slipped Al4C3 from the matrix. [ABSTRACT FROM AUTHOR]

The morphology and crystallography of E -(Al 18 Cr 2 Mg 3) nano dispersoids in 7475 Al alloy have been studied by using transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and electron tomography (ET). Seven distinct morphologies have been three-dimensionally distinguished at the nanoscale: (i) triangular plates on {111} Al , (ii) hexagonal plates on {111} Al , (iii) rods parallel to <110> Al , (iv) small tetrahedra with {111} Al facets, (v) small octahedra, (vi) spheres and (vii) irregular shapes. Twinning can contribute to the diverse morphologies of E nano dispersoids. The orientation relationships (ORs) between E nano dispersoids and Al matrix have been systematically investigated by selected area electron diffraction (SAED) patterns, HRTEM and matrix calculation. The results from the matrix calculation indicate the absence of clear ORs between E nano dispersoids and Al matrix in 7475 Al alloy. • The morphology of E -(Al 18 Cr 2 Mg 3) nano dispersoids in 7475 Al alloy have been studied by using electron tomography. • Seven distinct morphologies have been three-dimensionally distinguished at the nanoscale. • Twinning can contribute to the diverse morphologies of E nano dispersoids. • Based on matrix calculation, there are no clear orientation relationships between E dispersoids and Al matrix. [ABSTRACT FROM AUTHOR]

Pre-stretched strains, 2%, 4%, and 6%, were conducted on the friction-stir-welded dissimilar 2024-to-7075 aluminum alloy joints for strengthening purpose. Tensile tests and microhardness measurements were performed to evaluate the strengthening effect. Transmission electron microscopy and high resolution transmission electron microscopy examinations were employed to characterize precipitates and dislocation structures of the as-welded and pre-stretched joints to elucidate the intrinsic strengthening mechanisms. Results showed that the yield and tensile strengths of the pre-stretched 6% joint respectively increased 147.9 MPa and 31.1 MPa when compared with the as-welded joint. The strain hardening rates of 2024 lower hardness zone (LHZ)-II and 7075 LHZ were higher at the pre-stretched strain rate of 1 mm/min than those of 2 mm/min based on the microhardness area evolution. The yield sequence of the as-welded joint was 2024 LHZ-II, 2024 LHZ-I, 7075 LHZ, stir zone (SZ), and 2024 base material. The appearance of dislocation tangles, dislocation walls, dislocation cells, dislocation pile-ups in the 2024 LHZ-II and 7075 SZ combined with the severe interactions between dislocation structures and precipitates were the dominant strengthening factors. It was very interesting that dislocations provided a diffusion path for Mg atoms and Cu atoms in 2024 LHZ-II during the pre-stretching process. • Pre-stretching was used to strengthen the FSWed dissimilar aluminum alloys joints. • Yield sequence of the FSWed dissimilar aluminum alloys joints was identified. • The strengthened lower hardness zone contributed to the reinforced global joint. • Several kinds of dislocations structures induced by the pre-stretching process. • Dislocations provided a diffusion path for Mg and Cu atoms in 2024 aluminum alloy. [ABSTRACT FROM AUTHOR]

Hydrogen trapping is one of the factors leading to hydrogen embrittlement in heat-treatable high-strength aluminum alloys. The effect of coherency of precipitates on the corrosion-induced hydrogen trapping in aluminum alloy 2024 was investigated by performing artificial aging treatments before corrosion exposure. Two aging temperatures were employed, 170 and 210 °C, for aging times spanning the underaged, peak-aged and overaged conditions. Hydrogen uptake was induced by exfoliation corrosion. Hydrogen evolution from trapping sites was followed by thermal desorption spectroscopy. High resolution transmission electron microscopy combined with geometric phase analysis was performed to analyze the coherency of the precipitates. The results indicated that the coherency state between precipitates and the matrix plays an important role in hydrogen trapping. Hydrogen evolving at 300 °C (T2 state) corresponds to hydrogen trapped by the stress fields of coherent GPB zones and S΄΄ (Al 10 Cu 3 Mg 3) phases, which form at aging temperatures, below the corresponding solvus temperature. • Corrosion-induced hydrogen trapping in Al alloy 2024 has been elucidated. • The coherency state between precipitates and the matrix plays an important role in hydrogen trapping. • Hydrogen desorbed at 300 °C (T2 state) is trapped by stress fields of coherent GPB/S″ phases. [ABSTRACT FROM AUTHOR]

Dissimilar material (Al and steel) tubes have been successfully joined together using magnetic pulse welding technique by setting optimized parameters i.e., discharge voltage and standoff distance. The welded interface has revealed an irregular wavy morphology with melt pockets (max. width ∼20 μm) consisting of intermetallic compound embedded in elemental mixture. High resolution electron microscopy and compositional analysis through energy dispersive x-ray spectroscopy (EDXS) have revealed the formation of 2–3 μm long rod-shaped Fe-Al intermetallic compound. Non-destructive ultrasonic C-scans of the sample welded at 15.5 kV discharge voltage and 1.25 mm air gap have indicated sound welds between the two materials depicting 80% joint integrity while considering the backwall reflection threshold at 50%. The corrosion behaviour at the weld interfaces has been investigated in aqueous solution of 3.5 wt. % NaCl using both potentiodynamic and immersion tests revealing the influence of the intermetallic compound layer on corrosion. [Display omitted] • Non-destructive ultrasonic C-Scan characterization of magnetic pulse welded Al-Steel tubes. • Weld interface consists of 10–20 μm thick melt pockets of Al-Fe intermetallic. • The IMC layer thickness at the interface is directly proportional to the heat input that accelerates the corrosion rate. [ABSTRACT FROM AUTHOR]

The effects of a minor addition (0.4 wt%) of Ag to Al-5.1Cu-1.0 Mg aluminum alloy on the microstructural evolution and mechanical properties have been investigated. The under-ageing, peak ageing, over-ageing, and prolonged ageing at 185 °C were studied for the alloys with and without Ag additions to further correlate the microstructure with mechanical properties. The faster increment of hardness during the early stage (1–5 h) and much higher ultimate tensile strength (530 Mpa) at peak ageing condition in Ag-containing specimen were attributed to the formation of the Ω phase triggered by the Ag addition. In over-aged specimens, the S phase in the Ag-free specimen coarsened significantly, whereas the S phase in the Ag-containing specimen remained nearly the same size as that in its peak-ageing treated specimen. The formation of the Ω phase in the Ag-containing specimen presumably consumed the same solute atoms as the S phase, i.e., Cu and Mg, leading to the depleted zones of Cu–Mg in the aluminum matrix and thus suppressing the coarsening of the S phase during the ageing time from 11 h (peak ageing) to 18 h (over ageing). After ageing for 100 h (prolonged ageing), the S phase coalesced in both alloys. However, the Ω phase in the Ag-containing specimen still maintained a thickness of ∼3 nm with a high level of volume percent (2.74 vol %), which contributed significantly to the UTS (449 MPa). [Display omitted] • Microstructural evolutions and mechanical properties of Ag-free and Ag-containing AA2024 alloys have been investigated. • T6 UTS in Ag-containing alloy is 16 % higher than that of the Ag-free alloy, associating with its possession of Ω phase. • TEM results provide evidence that the coarsening of the S phase is suppressed by the Ω phase during a longer holding time. • HR-STEM studies show that after ageing at 185 °C for 100 h, the thermally stable Ω phase maintains a thickness of ∼3 nm. • Morphologies of non-edge-on Ω phase and S phase have also been investigated. [ABSTRACT FROM AUTHOR]

In this paper, we report that a selective laser melted (SLM) AlSi10Mg alloy has unique hierarchical microstructures. There are micro-sized Al grains and transgranular ultrafine cellular structures around primary Al, and the cell boundary is made up of alternate eutectic Si and eutectic Al phases. The SLM AlSi10Mg alloy has both high tensile strength and high strain-hardening capability, which are superior to Al-Si alloys fabricated by conventional powder metallurgy and cast methods. Post-tensile high-resolution microscopy analyses provide further evidence supporting Orowan looping as a strengthening mechanism of the SLM Al-Si alloy. [ABSTRACT FROM AUTHOR]

The effect of induced electro-pulsing of 7075 aluminum alloy in solid solution and pre-deformation was studied. The tensile test results show that material plasticity is recovered and strength is increased by induced electro-pulsing treatment (IEPT). As the discharge time increases, the increase in elongation becomes more obvious. Yield strength, tensile strength, and elongation of once-treated samples increased by 3.7%, 1.3%, and 9.7%, respectively, compared with the untreated sample; Those of twice-treated samples increased by 6.4%, 6.4%, and 27.8%. Microstructure characterization showed that the induced current reduces the dislocation density of the material and promotes advanced precipitation of Guinier-Preston (GP) zones. In addition, the strength of treated samples and untreated samples was almost the same after peak aging treatment, while the elongation increased by 12.15%. High resolution transmission electron microscopy (HRTEM) images show that the size of the η' phase in the treated alloy is smaller and the alloy exhibits better ductility. • Induced electro-pulsing treatment (IEPT) is used to improve the properties of 7075 aluminum alloy. • After IEPT, the plasticity of the alloy is significantly improved and the strength is slightly increased. • Induced current can promote the advance precipitation of GP region, which results in smaller η' phase after aging. [ABSTRACT FROM AUTHOR]

Abstract: High-resolution scanning transmission electron microscopy was used to investigate the core structure of a metadislocation in a plastically deformed sample of the complex metallic alloy ε 6-Al–Pd–Mn. The atomic-level characterization of a metadislocation with 16 associated phason planes showed dissociation into metadislocations with 6 and 10 phason planes. A structural model of the dissociated core region was developed. The Burgers vector of the dislocation = −0.07 nm [001] splits up into = −0.183 nm [001] and = 0.113 nm [001] increasing the strain at the metadislocation cores. Although unfavourable with respect to an increasing elastic strain energy the dissociation is realized due to a decrease in fault-plane energy. The latter arises from a size reduction of the ξ-phase area that is required to accommodate the metadislocation in the structure. A careful inspection of several exemplary metadislocations with 16 phason planes using electron microscopy indicates their dissociated structure which casts doubt on the stability of elementary metadislocations with 16 phason planes. The study includes a detailed analysis of the structure of a metadislocation core with 6 associated phason planes. [Copyright &y& Elsevier]

The link between microstructure, crystallographic texture and mechanical properties is of substantial importance to the understanding of materials behaviour of aluminium alloys. The favoured approach to determine these relations has been electron backscatter diffraction (EBSD) and has received extensive prior attention. However, compared to conventional optical microscopy, EBSD is both cost and potentially time intensive limiting its viability as a widespread method in industrial quality assurance. Following early successes by the authors and other investigators with optically birefringent metals, this investigation assesses the suitability of reflected circular polarized light microscopy (CPLM) as a rapid low-cost alternative to EBSD for cubic systems. Direct comparisons between EBSD crystal orientation maps (COMs) and a quantitative determination of the character of reflected polarized light images is presented to demonstrate that this technique can provide quantitative texture information for aluminium. Further, the inherently surface sensitive nature of the technique allowed further verification of orientation relationships between the substrate and surface oxide only previously made possible by high resolution transmission electron microscopy. • A novel approach that links polarized light microscopy with electron backscattered crystallographic analysis. • A new rapid crystallographic analysis method suitable for routine quality control. • Crystallographic analysis of anodized Aluminium using polarized light. • Insights into the symmetry and data recording of crystallographic data using commercially available software. [ABSTRACT FROM AUTHOR]

The microstructural evolution of Al-2.24 Cu-1.42 Mg-0.9 Fe-0.9 Ni (AA2618) alloy after 195 °C/18 h aging, as well as after 180 and 240 °C/100 h creep, has been studied by transmission electron microscopy and high resolution electron microscopy (HREM). The Guinier-Preston-Bagaryatsky (GPB) zones/co-clusters, S″, S, and AlFeNi phases co-exist in the alloys after the 195 °C/18 h aging. After creep, precipitates become coarser and the transformation of GPB zones/co-clusters and S″ to S phase take place. A large number of GPB zones/co-clusters as those in aging state exist after 180 °C/100 h creep which possibly dynamically precipitates during the creep process. After the 240 °C/100 h creep, most of the precipitates are S variants with a few GPB zones and S″ phase. More dislocations appear upon which precipitate colonies form after creep. HREM images show that most of the early precipitates less than about 5 nm cannot exhibit perfect lattice image for the existence of stress. However, certain GPB/co-clusters possessing coherent relationship with the matrix can also be observed. HREM demonstrates that certain S particles viewed along [100] and [013] have classic orientation relationship with the matrix, and that those upon the dislocations depart from the standard orientation. [ABSTRACT FROM AUTHOR]

Abstract: In this investigation the Al64Cu24Fe12 alloy was melted in an induction furnace and solidified under normal casting conditions. In order to obtain the icosahedral phase (i-phase) in a single-phase region, the as-cast sample was subject to a heat treatment at 700°C under argon atmosphere. Subsequently, the i-phase was milled for different times in order to evaluate phase stability under heavy deformation. X-ray diffraction (XRD) and high-resolution electron microscopy (HREM) analysis were conducted to the structural characterization of ball-milled powders. XRD results indicated a reduction in quasicrystal size during mechanical ball milling to about 30h. HREM analysis revealed the presence of aperiodic nano-domains, for example, with apparent fivefold symmetry axis. Therefore, the i-phase remains stable over the first 30h of ball-milling time. However, among 30–50h of mechanical milling the i-phase transforms progressively into β-cubic phase. [Copyright &y& Elsevier]

Abstract: We investigate dislocations in the complex metallic alloys T–Al–Mn–Pd and T–Al–Mn–Fe using high-resolution aberration-corrected scanning transmission electron microscopy. The dislocations consist of a large core and separated escort defects . Upon movement, dislocations and escort defects locally transform the material and introduce stacks of planar faults which represent a slab of a different but related structure. Deformation modes involving glide and climb are observed. We find different types of dislocations with Burgers vectors , with n =2, 3, 4. They are associated to two, four and six planar faults, respectively, and are identified as metadislocations. The structural connection between metadislocations in the present phase and those in R-, ε6-, and ξ-phases is discussed. [Copyright &y& Elsevier]

Extended twins, up to 100nm in length and occupying the length of an entire grain, are observed in an Al–4%Mg alloys/B4C nanocomposite material processed via high-temperature, high-strain-rate forging. High-resolution electron microscopy, used to identify the extended twins and to formulate the mechanism for their formation, indicates that they are created by the emission of 1/6〈112〉 twinning partial dislocations. The macroscopic origin is attributed to the local high stress field present during the forging process. [Copyright &y& Elsevier]

Abstract: Precise measurements of strain fields around precipitates embedded in a crystalline matrix were performed, and simple but accurate models were deduced from the observations. The measurements were carried out in an aged aluminum alloy containing needle-shaped particles. The displacement and strain fields around rod-shaped and lath-shaped particles were obtained from high-resolution electron micrographs using geometric phase analysis. The measurements reveal that strain field of a rod-shaped particle is well described by the classical Eshelby analytical elastic solution. For the more complex case of lath precipitates, it is shown that the strain field in the matrix can be simply approximated by a dislocations dipole. The methods developed are generally applicable to the characterization of strain in nano-structured materials, including those with complex or unknown structures. [ABSTRACT FROM AUTHOR]

Various orientations and diffraction patterns of metastable β″ precipitates during artificial aging are investigated by means of high-resolution electron microscopy and electron diffraction in Al–Mg–Si alloys. Twelve orientations of β″ precipitates with C-centered monoclinic crystal structure are analyzed systematically. The orientation relationships can be expressed as: (010)β″//{100}Al; [001]β″//<310>Al; [100]β″//<230>Al. In addition, a new diffraction patterns model from β″ precipitates in 12 orientations is established under the [001]Al zone axis. [Copyright &y& Elsevier]

Abstract: The formation of S-phase with a modified orientation relationship (OR) has been previously observed in several Al–Cu–Mg alloys. In this paper, high-resolution transmission electron microscopy and Z-contrast imaging have been used to study the origin of the modified OR in an alloy with low Cu/Mg ratio and small Si addition. Based on the observations, and supported by ab initio simulations, the formation is governed by coherency at the (021)S//(014)Al S-phase/matrix interface, which is shown to coexist with the more commonly reported (001)S//(021)Al interface. This new (021)S//(014)Al S-phase/matrix interface explanation is compared with previously published explanations based on the invariant line concept and establishment of a different S-phase/matrix interface. Energy dispersive X-ray spectroscopy and atom probe tomography indicate that the S-phase is slightly enriched in Si. The role of Si as well as the overall alloy composition is discussed. Because of the similarities between our results and the early work of Bagaryatsky, the S″-phase notation is adopted for this early-forming, strained version of the S-phase. [Copyright &y& Elsevier]

The effect of trace Ag on the early precipitation and the resistance to stress corrosion cracking (SCC) of peak-aged 7N01 alloy (Al-4.5Zn-1.55Mg-0.12Cu) were investigated. A characterization method known as three-dimensional atom probe (3DAP) was used in this research to investigate the precipitation behaviors of the alloy. When 0.12 wt % Ag is present in the alloy, the solid solubility of the alloy increases after the solid-solution treatment at 485 °C and quenching in water. In the early stage when the alloy is aged at 120 °C, Ag atoms will enrich around the clusters (GPI zones and GPII zones) giving rise to more nucleation sites for them. As the ageing time goes on, these clusters will transform into high-density η′ phase and then the hardness and mechanical strength of the alloy will increase. Three kinds of precipitates with different sizes in the alloy after peaking ageing were found by high resolution transmission electron microscopy (HRTEM). The results obtained from the high angle annular dark field of scanning transmission electron microscope (HAADF-STEM) show that Ag atoms are distributed around η′ phase in the matrix and η phase in the grain boundaries, which significantly increases the corrosion resistance of the alloy in NaCl solution after peak ageing. The results from the slow strain rate test (SSRT) and the observation of fracture morphologies show that for the alloy with trace Ag addition and after peak ageing, the resistance to SCC is improved, as well as the size and the distribution distance of the precipitate (MgZn 2) in the grain boundaries increase. • The formation of two kinds of GP zones was observed by 3DAP test directly. • Adding trace Ag significantly increases the density and size of GP zones. • Adding trace Ag is beneficial to the stress corrosion resistance of the alloy in NaCl solution. [ABSTRACT FROM AUTHOR]

The structure of Al3Zr precipitates in Al-1.0Mg-0.6Si-0.5Zr (in wt.%) alloy was investigated using conventional transmission electron microscopy (TEM) and high-resolution TEM (HREM). After annealing of the alloy in the temperature range 450–540 °C, spherical precipitates of metastable L12-Al3Zr phase appeared nearly homogeneously within the matrix, and elongated particles were found at grain boundaries. L12-structured Al3Zr were about 20–30 nm in diameter and coherent with the matrix. Inside some of them, planar faults parallel to {100} planes were revealed by use of HREM. Most probably, these faults are an indication of the transition stage of transformation to the stable D023-type Al3Zr phase. The elongated precipitates (about 100 nm) were identified as D022-type Al3Zr. Energy-dispersive X-ray analysis showed that they contain, apart from Al, mainly Zr with small amounts of Si. The substitution of Al by Si increased the stability of the D022-Al3Zr as compared with D023-Al3Zr. [ABSTRACT FROM AUTHOR]