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High salt content is one of the major problems for stewed products. To help address this issue, the effect of salt reduction on water migration in stewed ducks was investigated through diverse approaches, including water activity (Aw) and water-holding capacity (WHC) assay, as well as low-field nuclear magnetic resonance (LF-NMR) and scanning electron microscopy (SEM) observation. Our results showed that Aw value remained stable, while centrifugal loss decreased, and cooking loss increased significantly (p 0.05). The analysis of NMR indicated that, during the marinating stage, the proportion of immobilized water increased from 86.86%-89.66% (sodium chloride group) and 90.51% (salt-reduced group), respectively. After 2 h, the free water content became 0, and then became stable until the end of marinating. In the stewing stage, at the beginning 20 min, relaxation time of immobilized water decreased to about 35 ms and the ratio of immobilized water significantly reduced (p 0.05) by 5.38% (sodium chloride group) and 5.95% (salt-reduced group), respectively. Free water peak was detected upon stewing of 10 min, and 20 min later, there was no significant difference in the proportion of free water (p 0.05). In general, no significance was observed in water behavior and microstructure of stewed duck meat between the salt reduction group and sodium chloride group. In addition, SEM analysis revealed that marinating could expand the muscle fiber gap to accommodate more immobilized water. However, the fiber was looser at the initial stage of stewing and then became more compact. PRACTICAL APPLICATION: This work demonstrates potentially feasible to produce salt-reduced duck products.

Electrolysis of water is an effective way to produce high-purity hydrogen. Also, it is of great significance to develop an efficient electrocatalyst for hydrogen evolution reaction (HER), which is ...

A combination of X-ray computed tomography (CT) and focused ion beam - scanning electron microscopy (FIB-SEM) has been employed to investigate substrate and related surface defects in a niobium coated superconducting radio frequency (SRF) copper cavity. The cavity was manufactured by spinning, with subsequent application of a sputtering-deposited niobium coating (≈40 μm thick) on the internal surface. Before coating, the copper surface was pre-treated in several stages, ending with chemical polishing. CT and FIB-SEM identified furrow defects (≈20 μm deep) in the copper beneath the coating, which originated from the spinning process. The furrows were filled with niobium and contained voids at the Nb/Cu interface that extended a few microns into the niobium coating. The presence of the defects led to similar furrows at the niobium surface. The study revealed the importance of pre-treatment of the cavity internal surface and control of the spinning process to avoid defects that may have deleterious influence on the Q slope and durability of the niobium coating.

Nickel coating was obtained by potentiostatic electrodeposition in 1-butyl-3-methylimidazolium diethylphosphate ionic liquid without any additive. Further, cyclic voltammetry (CV) tests were used to investigate the electrochemical behaviour of Ni2+ in the ionic liquid, revealing that the electrodeposition of nickel in this ionic liquid is an irreversible process. It was revealed that the diffusion of Ni2+ is a rate-determining step in the electrodeposition process. Further, the influence of dissolved water and applied voltage on electrodeposition were also studied using scanning electron microscopy (SEM).

Active anti-corrosion pigments, such as strontium chromate, are essential components of many corrosion protective organic coatings, since these leach out to provide active inhibition to the metallic substrate at the defective areas of the coatings arising during service from mechanical and/or environmental damages. Currently, formulators use empirical tests to determine effective inhibitor concentration, because the factors that determine leaching behaviour are poorly understood. In this study, we present insights into leaching mechanisms by correlating the microstructure of model coatings pigmented with strontium aluminium polyphosphate hydrate (SAPH) to the transport of different species. It is found that diffusion and transport of active species through the polymeric matrix does not significantly contribute to the leaching kinetics. Thus, leaching starts when inhibitor pigments are in direct contact with the environment via surface-breaking defects in the coating, and continues as long as the cluster of connected inhibitor pigments is in direct contact with the environment, until 3-dimensional connectivity is lost. Therefore, the extent, shape and size of the clusters of connected inhibitor pigments, as well as the solubility and dissolution rates of individual pigments, play important roles in the leaching process. Additionally, the 3-dimensional percolation threshold (Pc) for pigment connectivity is proposed as a critical parameter that has significant influence on the leaching rate as well as the barrier properties of corrosion protective coatings.

High-spatial-resolution secondary ion mass spectrometry offers a method for mapping lithium at nanoscale lateral resolution. Practical implementation of this technique offers significant potential for revealing the distribution of Li-containing nanoscale precipitates in Al-Li alloys with exceptional lateral resolution and elemental sensitivity. Here, two state-of-the-art methods are demonstrated on an aluminium-lithium alloy to visualise nanoscale Li-rich phases by mapping the 7Li+ secondary ion. NanoSIMS 50L analysis with a radio frequency O− plasma ion source enabled visualisation of needle-shaped T1 (Al2CuLi) phases as small as 75 nm in width. A compact time-of-flight secondary ion mass spectrometry detector added to a focused ion beam scanning electron microscope facilitated mapping of the T1 phases down to 45 nm in width using a Ga+ ion beam. Correlation with high resolution electron microscopy confirms the identification of T1 precipitates, their sizes and distribution observed during SIMS mapping.

Recently, the dual beam Xe+ plasma focused ion beam (Xe+pFIB) instrument has attracted increasing interest for site‐specific transmission electron microscopy (TEM) sample preparation for a local region of interest as it shows several potential benefits compared to conventional Ga+FIB milling. Nevertheless, challenges and questions remain especially in terms of FIB‐induced artefacts, which hinder reliable S/TEM microstructural and compositional analysis. Here we examine the efficacy of using Xe+ pFIB as compared with conventional Ga+ FIB for TEM sample preparation of Al alloys. Three potential source of specimen preparation artefacts were examined, namely: (1) implantation‐induced defects such as amophisation, dislocations, or ‘bubble’ formation in the near‐surface region resulting from ion bombardment of the sample by the incident beam; (2) compositional artefacts due to implantation of the source ions and (3) material redeposition due to the milling process. It is shown that Xe+pFIB milling is able to produce improved STEM/TEM samples compared to those produced by Ga+ milling, and is therefore the preferred specimen preparation route. Strategies for minimising the artefacts induced by Xe+pFIB and Ga+FIB are also proposed. Lay Description FIB (focused ion beam) instruments have become one of the most important systems in the preparation of site‐specific TEM specimens, which are typically 50‐100 nm in thickness. TEM specimen preparation of Al alloys is particularly challenging, as convention Ga‐ion FIB produces artefacts in these materials that make microstructural analysis difficult or impossible. Recently, the use of noble gas ion sources, such as Xe, has markedly improved milling speeds and is being used for the preparation of various materials. Hence, it is necessary to investigate the structural defects formed during FIB milling and assess the ion‐induced chemical contamination in these TEM samples. Here we explore the feasibility and efficiency of using Xe+PFIB as a TEM sample preparation route for Al alloys in comparison with the conventional Ga+FIB.

The presence of alloying elements in aluminium alloys has a significant impact on the anodizing behaviour and results in the formation of porous anodic films with different chemical composition and morphology compared with those generated on pure aluminium. In this work, the effect of alloy element enrichment at the alloy/film interface and of cell diameter on the incorporation and distribution of alloying element species in porous anodic films is considered. It is proposed that above a critical cell diameter, Dcrit, the critical alloy enrichment sufficient for oxidation of the alloying element and its incorporation into the film can be maintained across the alloy/film interface. Below Dcrit, only a sub-critical enrichment can be maintained and the alloying element is then incorporated into the film at the cell boundaries. Dcrit depends on the concentration of the alloying element in solid solution and on the critical enrichment. The proposed role of Dcrit is supported by alloying element distributions from literature data for model Al-Au and Al-W alloys and new results for anodic films on AA 2024-T3 alloy.

In the present study, the impact of machining on the microstructure of AA7150-T651 aluminium alloy is investigated. It is found that a near-surface deformed layer is formed on the alloy due to severe shear strain during machining operation. The near-surface deformed layer of approximately 500 nm thickness distributes uniformly across the machined alloy surface. Ultrafine equiaxed grains with the dimensions of 50–100 nm are formed within the near-surface deformed layer. Further, the strengthening precipitates (MgZn2) that are initially present in the alloy in T651 temper are dissolved into the alloy matrix within the near-surface region. Subsequently, the dissolved alloying elements segregate at the grain boundaries of the newly formed fine grains in the near-surface deformed layer.

The present work investigates the corrosion behaviour of magnesium with different Fe contents. It is found that the micro-galvanic coupling between Fe-rich particles and magnesium matrix results in surface film formation and decrease in anodic reaction rate, consequently, increase of corrosion potential. Depending on the population density of Fe-rich particle, if the corrosion potential increases to the breakdown potential of surface film, localized corrosion initiates at the sites of breakdown. It is observed that Mg with different Fe contents exhibit the same critical potential value for corrosion initiation. Thus, corrosion potential is a critical factor for the corrosion tolerance limit of Fe in Mg.

An epoxy amine-based seawater ballast tank coating was characterized after 18 years of exposure to service environment. Coating flake specimens were taken from a flat region of the ballast tank, which appeared intact and well attached to the steel substrate. The flakes were examined using analytical electron microscopy and Fourier transform infrared (FTIR) spectroscopy. Significant morphological changes in the pigments and binder in the near surface region were observed. These were related to the hygrothermal cycles due to filling and discharge of sea water in the ballast tank, accompanied by cyclic temperature variations, generating expansion and contraction stresses within the coating. The analyses also reveal for the first time differences in the damage to barrier pigments (i.e. talc and kaolin) compared to the degradation of aluminium flake metal pigment. The former were fractured internally while the latter showed failure at the pigment/binder interface. Since pigments play a significant role on the degradation of the coating, their orientation towards the surface was also found to be of high importance. Regions of coating with pigments orientated nearly vertically to the surface showed a more severe degradation than regions with pigments orientated nearly parallel to the surface.

Manganese-catalyzed C2–H enaminylation of 1-(pyrimidin-2-yl)-1H-indoles with ketenimines is reported. The reaction provided 2-enaminylated indole derivatives in moderate to excellent yields with a broad substrate scope. A migration of the directing group pyrimidinyl occurred during this process. The synthesized 2-enaminyl indoles could be conveniently converted into 5-aryl-7H-benzo[c]carbazol-6-amines.

An experimental protocol (workflow) has been developed for time-lapse x-ray nanotomography (nano-CT) imaging of environmentally driven morphological changes to materials. Two case studies are presented. First, the leaching of nanoparticle corrosion inhibitor pigment from a polymer coating was followed over 14 days, while in the second case the corrosion damage to an AA2099 aluminium alloy was imaged over 12 hours. The protocol includes several novel aspects relevant to nano-CT with the use of a combination of x-ray absorption and phase contrast data to provide enhanced morphological and composition information, and hence reveal the best information to provide new insights into the changes of different phases over time. For the pigmented polymer coating containing nominally strontium aluminium polyphosphate, the strontium-rich components within the materials are observed to leach extensively whereas the aluminium-rich components are more resistant to dissolution. In the case of AA2099 it is found that the initial grain boundary corrosion is driven by the presence of copper-rich phases and is then followed by the corrosion of grains of specific orientation.

It is known that typical porous-type anodic films formed on aluminum and its alloys consist of two layers, i.e. a thick porous layer and thin barrier layer. However, the effect of the two layers on corrosion resistance of the anodic film is still not clear, which prevents a thorough understanding of the protection mechanism of the anodic film, thereby limiting the potential to further optimize the anodizing treatment. Herein, an electrochemical barrier layer thinning (EBLT) process was employed to reduce the thickness of the barrier layer of the porous-type anodic films formed on an AA2055 Al–Cu–Li alloy and pure aluminum. Then the structure and composition of the anodic films before and after immersion in a NaCl solution were studied in a comparison manner. It was found that the EBLT process evidently decreased the corrosion resistance of the anodic films formed on AA2055 alloy and pure aluminum. Thus, it was conclusively validated that the barrier layer of the porous-type anodic film played a decisive role in controlling the corrosion resistance of anodized aluminum and aluminum alloys prior to post sealing.

Joining of dissimilar light metals by friction stir welding (FSW) is of interest to reduce weight and fuel consumption in the transport sector. Such coupled metals may need protective surface treatments, e.g. against wear or corrosion, for some applications. In this work, the formation of plasma electrolytic oxidation (PEO) coatings in a silicate-based electrolyte for corrosion protection of FSW AZ31B magnesium alloy-titanium joints has been studied. The joints, if unprotected, may be susceptible to severe galvanic corrosion in chloride-containing environments. The coatings were characterized by scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction. Mg2SiO4 and MgO were identified in the coating on the AZ31B alloy and rutile and anatase on the titanium. Immersion of the joints in 3.5 wt% sodium chloride solution for 24 h resulted in severe corrosion of the AZ31B alloy in an uncoated joint; in contrast, corrosion of the AZ31B alloy was localized following PEO owing to the barrier protection provided by the coating. Corrosion of the titanium was negligible. The severe corrosion of the unprotected AZ31B alloy led to precipitation of a large amount of Mg(OH)2 from the sodium chloride solution by the end of the test. The weight of precipitate was reduced by a factor of ≈8 by the application of the PEO coating.

An organic primer pigmented with strontium aluminium polyphosphate for the corrosion protection of zinc alloy coated steel was investigated by electron microscopy and electrochemical impedance spectroscopy after exposure to sodium chloride solution. The development of defects within the organic coating was found to be related to the solubility of the pigment, which resulted in two conflicting effects. On the one hand, the inhibitive species released from the solid pigment reduced the corrosion rate of the metal substrate by formation of precipitated products containing zinc, strontium, aluminium, phosphorus and oxygen. On the other hand, the dissolution of the inhibitive pigment resulted in porosity in the coating that created easy pathways not only for the inhibitors to reach the substrate but also for the aggressive species to migrate inwards to the metal surface and, importantly, for the transport of corrosion products outwards.

A comparison has been made of the influence of two alloy pre-treatments and two coating post-treatments on the formation, composition and corrosion protection of a trivalent chromium conversion coating on AA2024-T351 alloy. The investigation employed analytical electron microscopies, ion beam analysis, X-ray photoelectron spectroscopy (XPS) and electrochemical tests. The pre-treatments used alkaline etching followed by de-oxidizing in either nitric acid or a commercial de-oxidizer. The conversion coatings were formed in SurTec 650 chromitAL and revealed two-layers, comprising an inner aluminium-rich layer and an outer chromium- and zirconium-rich layer, with a Cr:Zr atomic ratio in the range ~ 0.73–0.93. XPS indicated a chromium-enriched near-surface region that contained ~ 2 at.% of Cr(VI) species. Potentiodynamic polarization and electrochemical impedance spectroscopy revealed an improved corrosion protection for a pre-treatment that left copper-rich sponges, probably de-alloyed S phase, and fewer residues of other intermetallic particles on the alloy surface. Post-coating immersion treatments in deionized water at 20 °C or 40 °C resulted in a significant difference in the zirconium species in the region adjacent to the coating surface that is accessible to XPS, with oxide and hydroxide dominating at the respective temperatures.

The behaviour of Fe-containing particles during alkaline etching and desmutting of AA5052 aluminium alloy is investigated by quasi in situ monitoring of the compositional and morphological evolution of the particles. In alkaline solution, multi-layered oxide/hydroxide films are rapidly formed on the particles, rendering them electrochemically inactive. The particles are inactive in nitric acid due to formation of thin alumina layer. The treatment doesn’t significantly change the total population of Fe-containing particles with the population of Al3Fe being reduced and that of Al(Fe,Mn,Cr)Si remaining almost unchanged. Further, relevance of the observed behaviour to localized corrosion of aluminium alloys is also discussed.

In the present study, the behaviour of AA5754 and AA5052 alloys in alkaline solution is investigated using analytical electron microscopy. Significant differences in dissolution rate, change of intermetallic particle population density, compositional and morphological change of various intermetallic particles of the two alloys are observed. The dissolution rate of AA5754 alloy is approximately 1.3 μm/min., which is significantly lower than the dissolution rate of 2.3 μm/min. For AA5052 alloy. After alkaline etching, the population density of coarse intermetallic particles (mainly Mn-rich) on AA5754 alloy surface is significantly reduced whereas the population density of coarse intermetallic particles (mainly Fe-rich) on AA5052 alloy surface remains almost unchanged. Further, the root cause for the different behaviour of the two alloys in alkaline solution is discussed.

High strength Al-Zn-Mg-Cu (7xxx) aluminium alloys obtain the required balance of mechanical and corrosion properties through complex heat treatments developed through empirical experiment. Understanding the influence of these heat treatments on the composition of the strengthening precipitates (η′ and η-phase) is critical to obtain a better mechanistic understanding of their effect. In this work, the composition of strengthening precipitates has been studied at the atomic scale in microstructures of commercially processed AA7010 alloy in the standard overaged temper state. Copper enrichment in the precipitates on over-aging is confirmed for both small (η′) and large (η) particles. It is demonstrated that in addition to entering the precipitates, a copper enriched layer forms at the particle/matrix interface on the broad faces of the precipitate plates. The implications of this structure for the mechanical and environmentally assisted cracking performance of the alloy are discussed.

The recently reported superconductivity 9-15 K in Nd0.8Sr0.2NiO2/SrTiO3 heterostructures that were fabricated by a soft-chemical topotactic reduction approach based on precursor Nd0.8Sr0.2NiO3 thin films deposited on SrTiO3 substrates, has excited an immediate surge of research interest. To explore an alternative physical path instead of chemical reduction for realizing superconductivity in this compound, using pulsed laser deposition, we systematically fabricated 63 Nd0.8Sr0.2NiOx (NSNO) thin films at a wide range of oxygen partial pressures on various different oxide substrates. Transport measurements did not find any signature of superconductivity in all the 63 thin-film samples. With reducing the oxygen content in the NSNO films by lowering the deposition oxygen pressure, the NSNO films are getting more resistive and finally become insulating. Furthermore, we tried to cap a 20-nm-thick amorphous LaAlO3 layer on a Nd0.8Sr0.2NiO3 thin film deposited at a high oxygen pressure of 150 mTorr to create oxygen vacancies on its surface and did not succeed in higher conductivity either. Our experimental results together with the recent report on the absence of superconductivity in synthesized bulk Nd0.8Sr0.2NiO2 crystals suggest that the chemical reduction approach could be unique for yielding superconductivity in NSNO/SrTiO3 heterostructures. However, SrTiO3 substrates could be reduced to generate oxygen vacancies during the chemical reduction process as well, which may thus partially contribute to conductivity., Comment: 8 pages, 5 figures; Accepted in Rare Metals

Pigment distributions have a critical role in the corrosion protection properties of organic paint coatings, but they are difficult to image in 3D over statistically significant volumes and at sufficiently high spatial resolutions required for detailed analysis. Here we report, for the first time, large volume analytical serial sectioning tomography of an organic composite coating using a xenon Plasma Focused Ion Beam (PFIB) combined with secondary electron imaging, energy dispersive X-ray (EDX) spectrum imaging (SI) and electron backscattered diffraction (EBSD). Together these techniques provide a comprehensive quantitative description of the physical orientation and distribution of the pigments within a model marine ballast tank coating, as well as their crystallographic and elemental characterisation. Polymers and organic materials are challenging because of their propensity for ion beam damage and possible beam heating effects. Our novel, optimised block preparation technique permits automated data acquisition with minimal operator intervention, and can have significant applications for the structural and chemical characterisation of a wide range of organic materials. Our results revealed that the paint contained 7.5 vol% aluminium flakes and 25 vol% quartz particles. The aluminium flakes were oriented parallel to the substrate surface, which is beneficial in terms of the corrosion protection capability of the coating.

Electrolyzed oxidizing water (EOW) can be divided into acidic electrolyzed oxidizing water (AEOW) and slightly acidic electrolyzed water (SAEW). AEOW has the characteristics of low pH (pH2.7) and high oxidation-reduction potential (ORP1100 mV). SAEW is slightly acidic (pH = 5-6) and has an ORP of 700-900 mV. AEOW and SAEW both have a certain amount of active chlorine content (ACC), so they have the characteristics of broad spectrum, rapidity and high efficiency of sterilization. At present, there is little systematic research on AEOW and SAEW preparation. However, it is very important to study the preparation process, including electrode material and electrolytic process. First, the effects of Pt electrodes with different thermal decomposition temperatures on AEOW's pH, ORP and ACC values were investigated in detail. Next, for the SAEW preparation, the process is based on the preparation of AEOW by ion-exchange membrane electrolysis, reasonably mixing the electrolyzed cathode and anode solution. The effects of technological conditions such as electrolysis time, current density and electrolyte concentration have been systematically studied, and it is expected to get SAEW with a pH value slightly less than 7, a higher ORP value and a certain amount of ACC.

Corrosion behaviors of recently developed 2A97-T6 aluminum-copper-lithium alloy in sodium chloride solution are investigated using scanning electron and transmission electron microscopies in conjunction with electron backscatter diffraction. It has been found that corrosion product rings were established on the alloy surface as early as 5 min during immersion in sodium chloride solution. Meanwhile, hydrogen continuously evolved from within the rings. Pitting corrosion is evident with crystallographic dependant corrosion channel facets mainly parallel to {100} planes. Non-uniform distribution of misorientation in the 2A97 aluminum alloy results in a portion of grains of relatively high stored energy. Such grains were preferentially attacked, serving as local anodes, during the development of crystallographic pitting.

The protective film formed in a defect by leaching of lithium oxalate from model organic coatings during neutral salt spray exposure has been investigated. A scribed area of about 1 mm width was introduced on the coated AA2024-T3 aluminium alloy. The scribed area was examined before and after exposure in neutral salt spray environment for 4, 8, 24 and 168 h by scanning and transmission electron microscopies. It was found that the lithium oxalate was able to leach from the organic coating during neutral salt spray exposure and it promoted the formation of a film that provided effective corrosion protection to the alloy. The typical film morphology consists of three different layers, including a relatively compact layer near the alloy substrate, a porous middle layer and a columnar outer layer. Variation of the film morphology was also observed at different locations of the scribed alloy surface, which may be related to the difference of local concentration of lithium species. Electron energy loss spectroscopy detected lithium, aluminium and oxygen in the film. Although the film showed the varied morphologies in different regions of the scribed area, the alloy substrate was protected from corrosion when the film was formed. Copyright © 2016 John Wiley & Sons, Ltd.

A heterogeneous microstructure is intentionally developed in 2A97-T3 aluminium–copper–lithium alloy during solidification and thermomechanical processes to obtain good mechanical properties. As a consequence, the alloy is susceptible to localized corrosion. Electron microscopy was employed to observe intermetallic particles and their periphery and the initiation and development of intermetallic particle induced localized corrosion in 2A97-T3 aluminium–copper–lithium alloy. In-situ optical microscopy monitoring, energy dispersive X-ray spectroscopy and electron backscatter diffraction were also used to provide supportive evidence. Compared with the small number of continuous localized corrosion events, discontinuous localized corrosion event is relatively common. They are associated with corroded Al 2 Cu IM particles and Al–Cu–Fe–Mn-(Si) IM particles, as well as corrosion pits that are formed by particle fall-out due to dissolution of surrounding aluminium matrix. Discontinuous localized corrosion is confined within the shallow near-surface region of aluminium matrix. Triggered immediately after immersion, hydrogen gas evolution developed in form of bubbling at a continuous localized corrosion site which is associated with severe surface etching and sub-surface attack. Intergranular corrosion initiated from the corrosion pit bottom, connects to the corrosion pit via small openings, and developed into the large network buried underneath the alloy surface. T1 phase precipitate remnant and corroded IM particles at grain boundary induced dissolution in the periphery of the particle, drive intergranular corrosion to propagate. Copper is much less oxidized than aluminium and lithium during grain boundary attack, and therefore accumulated at the corrosion product – aluminium matrix interface in the intergranular corrosion filament. Then, the copper enrichment band acts as further local cathode to support reduction reactions.

The effect of anodization temperature and tartaric acid concentration on the morphology and corrosion resistance of the anodic film formed on AA2099-T8 alloy in tartaric-sulfuric acid was investigated. It was found that the dissolution of the anodic film during anodizing led to increased pore size, rod-shaped cavities and grain boundary grooves in the anodic films. The rod-shaped cavities and grain boundary grooves are associated with selective dissolution of the anodic film formed from fine T1 (Al2CuLi) phase precipitates due to the difference in the reactivity of the films formed from different phases. The increased porosity due to dissolution degraded the corrosion resistance of the anodic film. In the temperature range of 22–47°C, with 0.53 M tartaric acid addition, anodizing at 42°C provided the best corrosion performance and a relatively high anodizing efficiency; in the tartaric acid concentration range of 0–0.9 M, at 37°C, anodizing in electrolytes containing 0.7 and 0.9 M tartaric acid provided good corrosion resistance with little decrease of anodizing efficiency. The corrosive medium did not penetrate the anodic film uniformly but preferentially at local sites, resulting in localized corrosion of the anodized alloy.

The caustic etching behaviour of the automotive AA6111 alloy with different aging conditions that simulate the various levels of heat input within the heat affected zone during the welding heating cycles has been investigated. The alloy dissolution rate was found to substantially increase with the pre-aging temperature, which enhances precipitation of the cathodic Q-phase and results in depletion of the alloy solid solution in magnesium and silicon. On the other hand, enhancing the kinetics of precipitation at high temperatures induces a more uniform distribution the Q-phase precipitates, which minimizes the potential difference between the interiors and boundaries of the adjacent grains. This was observed to reduce the severity of the surface topography developed by subsequent caustic etching surface pre-treatment.

The effect of thermal exposure at 70 and 100 °C on intergranular corrosion (IGC) susceptibility of AA5083 alloy has been studied. At both temperatures, metastable β′ phase has been detected at grain boundaries. The thermal exposure resulted in sensitized microstructure in the alloy and, consequently, increased mass loss values during the nitric acid mass loss test (NAMLT). The sensitization of the alloy is related to the formation of the β′ phase. The as-received O temper alloy showed relatively high resistance to IGC and exhibited a discontinuous distribution of the β′ phase precipitates at grain boundaries. After exposure at 70 °C for 480 h, the size of β′ phase precipitate at the grain boundaries slightly increased, resulting in an increased mass loss. After exposure at 100 °C for 240 h, the alloy became severely sensitized due to the more continuous distribution of β′ phase precipitate along the grain boundaries.

This paper investigates the structure of the copper–enriched layer formed at the alloy/anodic film interface during anodizing of Al–2 wt.% Cu binary alloy using transmission electron microscopy. It was revealed that θ ′ phase was formed within the copper–enriched layer. For the copper–enriched layer formed on {1 0 0} aluminum planes, the interface between the aluminum matrix and the θ ′ phase within the copper-enriched layer is coherent. For the copper–enriched layer formed on {1 1 0} and {1 1 1} aluminum planes, the interfaces between the aluminum matrix and the θ ′ phase within the copper-enriched layer are semi-coherent or incoherent. The interfacial coherency influences the formation of oxygen gas bubbles within the resultant anodic films.

The formation of a trivalent conversion coating on aluminium has been investigated using analytical electron microscopy, atomic force microscopy, ion beam analysis, glow discharge optical emission spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The coating is shown to comprise a chromium- and zirconium-rich outer layer and an aluminium-rich inner layer. Zirconium and chromium are present in chemical states consistent with ZrO 2 , ZrF 4 , Cr(OH) 3 , Cr 2 (SO 4 ) 3 , CrF 3 and CrO 3 or CrO 4 2 − . However, negligible amounts of Cr(VI) species occurred in coatings formed in de-aerated solution. Electrochemical impedance spectroscopy revealed that the inner layer provides the main corrosion protection during short-term tests in 0.1 M sodium sulphate solution at room temperature.

Stress corrosion cracks of all types are characterised by extensive crack branching, and this is frequently used as the key failure analysis characteristic to identify this type of cracking. For aluminium alloys, stress corrosion cracking (SCC) is almost exclusively an intergranular failure mechanism. For plate and extruded components, this had led to the development of test procedures using double cantilever beam and compact tension precracked specimens that rely on the pancake grain shape to constrain cracking, so that fracture mechanics can be applied to the analysis of stress intensity and crack velocity and the evolution of a characteristic performance curve. We have used X-ray computed tomography to examine in detail SCC in aluminium alloys in three dimensions for the first time. We have found that crack branching limits the stress intensity at the crack tip as the applied stress is shared amongst a number of cracks that are held together by uncracked ligaments. We propose that the plateau region observed in the v-K curve is an artefact due to crack branching, and at the crack tips of the many crack branches, cracking essentially occurs at constant K almost irrespective of the crack length. We have amplified the crack branching effect by examining a sample where the long axis of the pancake grains was inclined to the applied stressing direction. Our results have profound implications for the future use of precracked specimens for SCC susceptibility testing and the interpretation of results from these tests.

Localized corrosion in an AA2099-T83 aluminum–lithium alloy has been correlated with localized plastic deformation (LPD) introduced by cold working. The high population density of dislocations in the slip bands associated with LPD promoted preferential precipitation of needle-shaped T1 (Al2CuLi) phase during artificial aging. Consequently, preferential attack of the electrochemically active T1 phase in corrosive environment resulted in selective corrosion of the bands, leading to the development of the characteristic morphology of narrow, parallel volume of corrosion. Copyright © 2015 John Wiley & Sons, Ltd.

It was revealed that an AA5083 alloy had been severely sensitized after 40 years in service at ground atmosphere temperature. The degree of sensitization of the various regions through the alloy plate thickness is different, which is associated with the non-uniform distribution of Mg through the plate thickness. The alloy plate exhibits Mg-rich bands that promoted the heterogeneous distribution of Mg-containing precipitates. The composition of these precipitates ranges from that for low Mg content intermetallics to that of the β′ phase. Structure characterization revealed the β′ phase and a cubic Al-Mg phase that has lower magnesium contents compared to the β phase.

The influence of prolonged ambient temperature storage on the subsequent precipitation behavior of the AA6111-T4P automotive alloy during artificial aging has been investigated using hardness testing and high-resolution transmission electron microscopy. The results indicate that growth of atomic co-clusters and GP zones during ambient storage suppress the onset of Q′ and Q precipitation, and retard the formation of elemental silicon particles. However, the overall hardening response of the stored AA6111 T4P alloy to subsequent peak-aging and over-aging treatments is not altered by the significant reduction in the volume fraction of Q′ and Q precipitates due to their lower strengthening effects compared with GP zones and the Q″ phase precipitates.

The corrosion behavior of intermetallic particles and their role in the process of localized corrosion in AA2099-T83 aluminum–lithium alloy has been investigated. It was found that both high- and low-copper containing Al–Fe–Mn–Cu-(Li) particles could result in superficial pits on the alloy, and the high level of lithium in the high-copper-containing particles rendered them electrochemically more active than the low-copper-containing particles. Additionally, severe localized corrosion was found not to be directly related to the distribution of constituent particles in the alloy. The findings are not only relevant to the understanding of corrosion mechanism but also beneficial to the evaluation of thermomechanical treatments of the alloy.

Special Issue: Proceedings 8th Symposium “Aluminium Surface Science and Technology”. The authors wish to thank Innoval Technology Ltd. for permission to publish this work. The cleaning of rolled aluminium surfaces is of critical importance for most applications and is of particular importance in automotive applications. The cleanliness of the sheet surface is mainly determined by the residual amount of the near-surface deformed layer on the alloy surface. This layer has nano-sized grains with their grain boundaries decorated and pinned by oxide particles and lubricant residues. The deformed layer reduces the reflectivity of the sheet or strip surface to visible light, particularly in the short wavelength range, resulting in a brownish appearance. Based on the optical characteristics of the deformed layer, the use of optical microscopy, spectrophotometry, and colourimetry has been evaluated to provide a quantitative measurement of the level of cleanliness. These latter evaluations have been cross-checked by using scanning electron microscopy and transmission electron microscopy on ultramicrotomed cross sections of aluminium sheet samples subjected to different level of cleaning to determine the amount of residual near-surface deformed layer.

In the present study, the influence of precipitate distribution on the corrosion behaviour of 2A97-T6 Al-Cu-Li alloy in 3.5 wt.% NaCl solution is investigated. It is found that localized plastic strain introduced to the alloy during sheet fabrication leads to the formation of dense T1 (Al2CuLi) phase precipitate bands and precipitate-free bands within selected grains during aging. Preferential dissolution of T1 phase in the dense precipitate bands results in intragranular corrosion in the alloy, in the form of corrosion bands. Further, the dissolution of the alloy matrix propagates in the form of crystallographic corrosion pit.

The anodizing behavior of a dissimilar friction stir weld of AA5083-O and AA6082-T6 alloys in 4 M H2SO4 solution has been investigated. The anodizing results show that the AA5083-O rich zones were more oxidized during anodizing compared with the AA6082-T6 rich zones. Interestingly, the nugget and the thermomechanically affected regions of the individual parent alloys showed significant reduction in porous anodic oxide thicknesses. Sputtering-deposition of pure aluminum on the weld, prior to anodizing, significantly minimized the variations in the oxide thicknesses across the weld. More importantly, this method prevented the boundary dissolution (associated with the activity of the Mg2Si phase) that is often observed after anodizing the dissimilar weld of the alloys.

Fe-rich particles that contain silicon were observed in commercially pure magnesium, which contained less than 25 ppm Fe. Based on the simulated phase diagram, silicon, even at low ppm levels, promotes the formation and growth of Fe-rich particles. The studied pure Mg showed a high corrosion rate (>2 mm/year) in 3.5 wt.% NaCl solution, although the Fe content is far below the widely accepted corrosion tolerance limit of Fe (170 ppm by weight). The formation of the Si-containing Fe-rich particles is one of the main reasons for the high corrosion rate observed. Consequently and importantly, the corrosion tolerance limit of iron in magnesium is significantly reduced by the presence of traces of silicon.

In the present study, time-evolved (4D) correlative 3D imaging techniques, combining microtomography and nanotomography with 3D FIB-SEM sectioning and EDS, have allowed shedding light on morphological and compositional aspects of the corrosion behaviour of AZ31 magnesium alloy. By applying these techniques, the corrosion processes involved, corrosion stages I, II and III, were identified successfully despite the challenging fast corrosion behaviour of magnesium-based alloys. The 3D reconstruction confirmed the near-surface restriction of the filiform corrosion (stage II) and the subsequent severe inward corrosion during stage III. Furthermore, the distribution of the coarse Al–Mn intermetallic particles could be correlated with the corrosion front development.

A correlation has been revealed between the localised corrosion susceptibility and the grain stored energy in AA2099-T8 aluminium alloy, with grains of higher stored energy being relatively more susceptible to corrosion attack. The grains of high stored energy contain increased crystallographic defects, which could consequently decrease their corrosion resistance. Additionally, since crystallographic defects are preferential sites for the precipitation of T1 (Al2CuLi) phase, it is suggested that grains of high stored energy could also contain increased volume fraction of T1 phase after aging, which might further increase corrosion susceptibility due to the electrochemically high activity of lithium rich T1 phase.

Microstructural characterisation of 2A97-T4 aluminium–lithium alloy was carried out using electron probe microanalysis and transmission electron microscopy (TEM). Scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy facilities has been employed to examine localised corrosion sites after immersion in sodium chloride solution. A dual beam microscope, which integrates a focused ion beam and an electron beam in one powerful instrument, has also been employed to investigate the development of intergranular corrosion from both surface and cross-section. It was found that localised corrosion is generally initiated at θ phase particles, which represents only 8.4% of the intermetallic (IM) particles in 2A97-T4 aluminium–lithium alloy. θ phase particles exhibit preferential dissolution of aluminium during corrosion testing, with trench formed at their periphery as well. Initiation of intergranular corrosion is relatively late with respect to the attack of IM particles. Owing...

Model organic coatings were formulated with different volume concentrations of strontium aluminium polyphosphate (SAPH) inhibitor pigment. Leaching measurements were performed from the top surfaces of the coatings. The microstructure of the coatings and the distribution of phosphorus and strontium within the coatings prior to and after exposure to an aggressive environment were characterized by SEM, EDS and EDXRF. The increase in inhibitor pigment volume concentration (PVC) results in the formation of larger clusters of connected inhibitor pigments within the coatings, which coincides with higher leaching rates from the coatings with higher inhibitor PVC. It is revealed that in the presence of the large clusters, the concentrations of inhibitor pigments decreases through the entire thickness of the exposed coating. In contrast, when the inhibitor PVC is low and elongated clusters of inhibitor pigments do not span the thickness of the coating, the reduction of the inhibitor pigment concentration within the exposed coating is limited to regions closer to the coating/environment interface. On the other hand, EDS analysis shows that after exposure, the concentrations of species released from the inhibitor pigments are below the detection limit within the polymeric binder. It is also shown that the diffusion through the polymeric binder would appear to be the limiting factor that retards the leaching from the coating, suggesting that diffusion through the polymeric binder is not the dominant transport mechanism for leaching of species released from the inhibitor pigments. A cluster model appears to describe well the leaching of inhibitive species released from the SAPH inhibitor pigments incorporated into the organic coatings.

MgB2 particles have been incorporated into a coating formed by AC plasma electrolytic oxidation (PEO) on aluminium under a constant current density. The incorporation of MgB2 into the coating was characterized by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. The additions of particles to the electrolyte promoted a voltage decrease, possibly a result of the initiation of a “soft” sparking regime. The transition occurred at earlier times with increase of the MgB2 concentration and enhanced MgB2 incorporation into the coating. The coating containing particles was thicker than one in which MgB2 was absent and had a nodular surface, with MgB2 accumulations in the valleys between the nodules. A superconducting quantum interference device revealed superconductivity below about 39 K, the critical temperature of MgB2, and hysteresis in magnetic moment-field curves that typifies a type II superconductor.

Linear friction welding may be used to join titanium alloys to stainless steel for a variety of applications. After welding, a crevice is often observed close to the edges and, in aqueous wet environments, a galvanic couple is formed between the two materials. If corrosion resistance is a requirement, the combined presence of a crevice and a galvanic couple is a concern. In this study, the behaviour of galvanically coupled titanium alloy and stainless steel has been investigated, both for planar electrodes and under simulated crevice conditions. In both cases, it was found that a significant driving force between the two materials develops over time to progress corrosion on the stainless steel, but the high specific impedance of the titanium surface limits the current flow. Consequently, it is concluded that galvanic coupling between titanium and stainless steel is only of concern if the area of the titanium largely exceeds the area of the steel, and only under complete immersion conditions in a sufficiently conductive electrolyte.

The effect of the anodizing process parameters and the influence of β'(Mg2Si) phase on the appearance of the anodized AA6063 aluminum alloy have been investigated. It was found that β'(Mg2Si) phase was preferentially oxidized at low anodizing voltages and the selective oxidation of β'(Mg2Si) phase resulted in the development of a rough alloy/film interface and the incorporation of silicon into the porous anodic film, which led to the discoloration of the anodized alloy.

High strength aluminium alloys provide benefits in vehicle efficiency and reduced energy consumption. Weldable, low copper 7xxx aluminium alloys are being developed for body-in-white production. Here, the influences of thermomechanical history on microstructure and, consequently, on the corrosion behaviour of lean 7xxx aluminium alloy sheet have been investigated. Cold worked microstructures in the alloys studied are susceptible to sub-surface cracking after accelerated corrosion testing. High resolution transmission electron microscopy (HAADF) with allied EDX analysis of a warm rolled alloy has revealed significant differences between some grain boundaries, showing differences in grain boundary precipitate distribution, which is influenced by grain misorientation and thermomechanical processing history. Possible relationships between the previously described phenomena are being sought. Electron backscatter diffraction has been employed to provide crystallographic information concerning grain orientation relationships from specific areas surrounding the attacked microstructure.