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Copyright © 2022 The Author(s). In this study, the composition templating theory for heterogeneous nucleation was applied to achieve TiB2 particles with Mn segregation on the surface, which supplied the initial composition for the heterogeneous nucleation. The interfacial segregation of added alloy element Mn and the other common impurities, such as Fe and Si, was investigated with scanning transmission electron microscopy (STEM). The modified TiB2 particles was applied in Al-2.0Mn-1.0Fe alloys to test its effects on grain refinement of Al6(Fe,Mn) compound. The interfaces between Al6(Fe,Mn) particles and the engulfed TiB2 particles were examined with TEM observation. Engineering and Physical Sciences Research Council (EPSRC) Grant EP/H026177/1.

Ferrimagnetic materials have recently been highly focused in the area of spintronics. In this work, epitaxial single-crystal ferrimagnetic Mn3Ga thin films with perpendicular magnetic anisotropy were fabricated by optimizing the sputtering growth temperature. The exchange coupling to a soft ferromagnetic CoFe layer, anisotropic magnetoresistance, the anomalous Hall effect, and the effect of measuring current on the zero-field anomalous Hall resistance were investigated. An anomalous anisotropic magnetoresistance was observed for this perpendicular magnetized material, which may provide evidence for the recently predicted Weyl points in ferrimagnetic Mn3Ga. In addition, this work may pave the way to current-induced magnetization switching assisted by Weyl-points-generated Berry curvature in a single ferrimagnetic layer under zero magnetic field.

Al-5Ti-1B is the most widely used grain refiner for Al alloys. However, it is not effective for grain refining Al alloys containing more than 3 wt pct Si. This adverse effect of Si is referred to as Si poisoning. In spite of extensive experimental and theoretical investigations in the past decades, the exact mechanism for Si poisoning is still not clear. In this work, the state-of-the-art electron microscopy was performed to investigate the mechanism for Si poisoning. Our experimental results suggest that Si segregates preferably to the TiB2/Al-Si melt interface and the pre-existing Al3Ti 2-dimensional compound (2DC) layer on TiB2 surface dissolves into the Al-Si melt. Based on the experimental results, we have postulated a new mechanism for Si poisoning: interfacial segregation of Si leads to enrichment of Si at the TiB2/Al-Si melt interface, and this in turn makes the pre-existing Al3Ti 2DC on the TiB2 surface unstable and dissolve gradually in the melt, resulting in a loss of TiB2 nucleation potency and hence a decreased total number of potent TiB2 particles available for heterogeneous nucleation and grain initiation and consequently an increased grain size. This mechanism for Si poisoning can explain consistently the experimentally observed phenomenon reported in the literature.

The microstructure and the filiform corrosion behaviour of machined AA7150 aluminium alloy were investigated using scanning and transmission electron microscopies combined with potentiodynamic polarization and filiform corrosion testing, respectively. It is found that the grain refinement, redistribution of alloying elements, and elements segregation at grain boundaries are evident within the near-surface region on the machined AA7150 aluminium alloy. The corrosion susceptibility of machining introduced near-surface deformed layer is significantly improved caused by the modified microstructure associated with severe deformation. Filiform corrosion resistance on the machined surface is obviously decreased, due to the surface roughness associated with machining tracks and the presence of the electrochemically more active near-surface deformed layer introduced by machining.

The emergence of the infinite-layer superconducting nickelate thin films marks the Ni age of superconductivity, which has excited a huge surge of studies since the first report in August of 2019. Despite of the tremendous attention drawn from the entire material science community and a large body of theoretical studies, the experimental progress has been relatively slow due to the challenging sample fabrication, which may, in turn, be holding back the fast development of theoretical research. Therefore, a timely and comprehensive review on all the up-to-date experimental progress of the emergent infinite-layer Ni-based superconductors is urgently needed. In this review, we first introduce the history of more than 30-year-long Ni-based superconductivity exploration, then summarize the sample fabrication processes, later present the experimental electrical transport and magnetic properties, and finally come up with several key issues deserving intensive studies. This review is thus expected to be helpful for researchers with diverse research background to readily capture the major progress of this emerging field., Comment: 36 pages, 23 figures, a review article published online at Materials Today

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.

Our world is composed of various materials with different structures, where spin structures have been playing a pivotal role in spintronic devices of the contemporary information technology. Apart from conventional collinear spin materials such as collinear ferromagnets and collinear antiferromagnetically coupled materials, noncollinear spintronic materials have emerged as hot spots of research attention owing to exotic physical phenomena. In this Review, we firstly introduce two types noncollinear spin structures, i.e., the chiral spin structure that yields real-space Berry phases and the coplanar noncollinear spin structure that could generate momentum-space Berry phases, and then move to relevant novel physical phenomena including topological Hall effect, anomalous Hall effect, multiferroic, Weyl fermions, spin-polarized current, and spin Hall effect without spin-orbit coupling in these noncollinear spin systems. Afterwards, we summarize and elaborate the electric-field control of the noncollinear spin structure and related physical effects, which could enable ultralow power spintronic devices in future. In the final outlook part, we emphasize the importance and possible routes for experimentally detecting the intriguing theoretically predicted spin-polarized current, verifying the spin Hall effect in the absence of spin-orbit coupling and exploring the anisotropic magnetoresistance and domain-wall-related magnetoresistance effects for noncollinear antiferromagnetic materials., 34 pages, 20 figures, Review Article in Rare Metals

The precipitation kinetics of overlapping process from nucleation and growth to coarsening of the γ′(Ni3Al) phase in Ni–Al alloys are investigated quantitatively by using the interface diffusion-controlled phase field model. It is found that the time exponent of average particles radius of the γ′ phase is about 1/3 at the growth and coarsening stage, while the exponent is smaller than 1/3 at the later steady-state coarsening stage. The decrease rate of the number density of the γ′ phase is larger at the steady-state coarsening than that of the growth and coarsening stage. The particle size distribution (PSD) is widened at the nucleation and growth stage, then is narrowed at the growth and coarsening stage, and becomes wide again at the steady-state coarsening stage; the width of PSDs obtained by the quantitative calculation is greater than 0.215 proposed by the LSW theory. Moreover, the position of the PSDs peak moves from 1.0 of the normalized radius at the nucleation and growth stage to less than 1.0 of the growth and coarsening stage, and then moves back to 1.0 at steady-state coarsening stage. The non-monotonically variation of kinetics of the γ′ phase during the precipitation process are reasonable and theoretically significant for the kinetics evolution.

The relative significance of quantum conductivity correction and magnetic nature of electrons in understanding the intriguing low-temperature resistivity minimum and negative magnetoresistance of the two-dimensional electron gas at LaAlO3/SrTiO3 interfaces has been a long outstanding issue since its discovery. Here we report a comparative magnetotransport study on amorphous and oxygen-annealed crystalline LaAlO3/SrTiO3 heterostructures at a relatively high-temperature range, where the orbital scattering is largely suppressed by thermal fluctuations. Despite of a predominantly negative out-of-plane magnetoresistance effect for both, the magnetotransport is isotropic for amorphous LaAlO3/SrTiO3 while strongly anisotropic and well falls into a two-dimensional quantum correction frame for annealed crystalline LaAlO3/SrTiO3. These results clearly indicate that a large portion of electrons from oxygen vacancies are localized at low temperatures, serving as magnetic centers, while the electrons from the polar field are only weakly localized due to constructive interference between time-reversed electron paths in the clean limit and no signature of magnetic nature is visible., 9 pages, 4 figures. Accepted in Journal of Physics: Condensed Matter

Due to the lack of any magnetic order down to 1.7 K in the parent bulk compound NdNiO2, the recently discovered 9-15 K superconductivity in the infinite-layer Nd0.8Sr0.2NiO2 thin films has provided an exciting playground for unearthing new superconductivity mechanisms. In this letter, we report the successful synthesis of a series of superconducting Nd0.8Sr0.2NiO2 thin films ranging from 8 to 40 nm. We observe the large exchange bias effect between the superconducting Nd0.8Sr0.2NiO2 films and a thin ferromagnetic layer, which suggests the existence of the antiferromagnetic order. Furthermore, the existence of the antiferromagnetic order is evidenced by X-ray magnetic linear dichroism measurements. These experimental results are fundamentally critical for the current field., Comment: 25 pages, 22 figure, 1 table. The manuscript is in press at Advanced Materials

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.

Hexavalent Chromium has been successfully employed for corrosion protection purposes in aerospace coatings for decades. However, legislation will restrict the use of Cr6+ in the future and therefore the aerospace sector needs to identify alternative environmentally friendly coatings for corrosion protection. Before implementation of newly developed systems into actual components is possible, rigorous and time-consuming testing practices are required to ensure the new systems can achieve the strict aerospace standards requirements. The emerging number of coating systems being developed, and the vast research conducted on the subject worldwide, make the selection of suitable replacements for industrial application challenging. In this work, differently pretreated aluminium AA2024 alloy surfaces are coated with conventional Cr6+ containing coating and compared to a number of industrial alternative coatings. Corrosion performance is assessed by real-time imaging while immersed, by EIS, and by standardised salt-spray tests. Results reveal that the performance ranking acquired by salt-spray tests (SST) can be readily replaced by short-term immersion tests, and the time to failure in SST can be estimated from key corrosion indicators arising from EIS measurements at specific immersion times.

We report the successful fabrication of noncollinear antiferromagnetic D019 Mn3Ge thin films on insulating oxide substrates. The anomalous Hall effect, and the large parallel negative magnetoresist...

The effects of applied current density, anodizing time and electrolyte temperature on the cell and pore morphology of anodic films and the voltage-time response obtained during galvanostatic anodizing of AA2024-T3 alloy in sulphuric acid electrolytes have been studied. Scanning electron microscopy was employed to observe the film morphology. Sponge-like porous structure was promoted by anodizing at relatively low current density and high electrolyte temperature. In contrast, linear porous structure was favoured under the converse conditions. Intermediate conditions resulted in films containing either sequential layers of the two morphologies or a morphology incorporating features of the two types; such conditions were associated with anodizing voltages in the range 25 to 35 V. The reasons for the morphological differences are proposed to be due to interactions between film growth stresses and stresses arising from oxygen evolution on the development of the alumina cells.

The microstructure and mechanical properties of friction stir welded 7055 aluminium alloy under air cooling and water cooling were investigated by means of hardness and tensile testing, optical microscopy and transmission electron microscopy. Water cooling results in reduced softening in the weld zone and therefore higher tensile strength compared to air cooling. Fracture generally occurs within the thermo-mechanically affected zone (TMAZ) and heat affected zone (HAZ) on the retreating side in joints welded under air cooling but shifts towards the TMAZ and nugget zone (NZ) in the joints welded under water cooling. The fracture surfaces are generally flat for the air-cooled joint, but exhibits a zig-zag feature for the water-cooled joint. The mechanical behaviour of the weld has been discussed in light of the change in grain structure and precipitation in the NZ, TMAZ and HAZ caused by cooling conditions.

Thick-section plates made from a recently developed Al–Cu–Mg–Li alloy have been evaluated to understand the influence of microstructure on the anisotropy of tensile strengths after natural and artificial ageing treatment. Pancake-shaped grains with a coarse substructure and strong crystallographic texture with a β-fibre orientation at the mid-thickness position are observed. In addition, an inhomogeneous distribution of T1 precipitates through the plate thickness has been revealed with the volume fraction of intragranular precipitates ∼40% higher at the plate centre than the ¼ thickness position. Altogether these microstructural features contribute to the in-plane anisotropy of tensile strengths that is ∼5% higher at the mid-thickness position than the ¼ thickness position. The variation of ageing-induced T1 precipitates through the plate thickness further contributes to the through-thickness anisotropy that is ∼3% higher in T8 temper as compared to T3 temper.

The precipitation kinetics of γ phase in the inverse Ni–20.4 at. % Al alloy are studied by utilizing phase-field method, combining with the volume fraction, particles number density, average particle radius, average aspect ratio and particle size distribution (PSD) of γ phase at different aging temperatures. It is found that the decrease rate of particles number density increases with the elevated aging temperature, and the decrease rate in the early coarsening stage are greater than that in the stable coarsening stage. The average particle radius shows a linear relationship with time through kt 1/3 in the stable coarsening stage of the inverse Ni–Al alloy, and the coarsening rate constant k increases with the elevated temperature. As the aging progresses, the peak value of PSD becomes smaller and the normalized radius r / r > moves from 1.1 to 1.0, while the peak value of PSD becomes larger and the corresponding r / r > value moves from 0.9 to 1.0 with the elevated temperature. The peak value of PSD is less than that predicted by Lifshitz-Slyozov-Wagner (LSW) theory at different aging temperatures.

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.

Non-collinear antiferromagnetic materials have received dramatically increasing attention in the field of spintronics as their exotic topological features such as the Berry-curvature-induced anomalous Hall effect and possible magnetic Weyl states could be utilized in future topological antiferromagnetic spintronic devices. In this work, we report the successful integration of the antiferromagnetic metal Mn3Sn thin films onto ferroelectric oxide PMN-PT. By optimizing growth, we realized the large anomalous Hall effect with small switching magnetic fields of several tens mT fully comparable to those of bulk Mn3Sn single crystals, anisotropic magnetoresistance and negative parallel magnetoresistance in Mn3Sn thin films with antiferromagnetic order, which are similar to the signatures of the Weyl state in bulk Mn3Sn single crystals. More importantly, we found that the anomalous Hall effect in antiferromagnetic Mn3Sn thin films can be manipulated by electric fields applied onto the ferroelectric materials, thus demonstrating the feasibility of Mn3Sn-based topological spintronic devices operated in an ultralow power manner., 25 pages, 10 figure. Accepted in Acta Materialia

In recent years, the field of antiferromagnetic spintronics has been substantially advanced. Electric-field control is a promising approach to achieving ultra-low power spintronic devices via suppressing Joule heating. In this article, cutting-edge research, including electric-field modulation of antiferromagnetic spintronic devices using strain, ionic liquids, dielectric materials, and electrochemical ionic migration, are comprehensively reviewed. Various emergent topics such as the Neel spin-orbit torque, chiral spintronics, topological antiferromagnetic spintronics, anisotropic magnetoresistance, memory devices, two-dimensional magnetism, and magneto-ionic modulation with respect to antiferromagnets are examined. In conclusion, we envision the possibility of realizing high-quality room-temperature antiferromagnetic tunnel junctions, antiferromagnetic spin logic devices, and artificial antiferromagnetic neurons. It is expected that this work provides an appropriate and forward-looking perspective that will promote the rapid development of this field., Comment: 47 pages, 21 figures. Review

Coalescence coarsening and Ostwald ripening as well as the kinetics of γ precipitation in the γ′ matrix of inverse Ni–Al alloys are investigated by phase field simulations. The ordering of the γ′ matrix during the initial phase transformation of inverse Ni–Al alloys is faster than clustering, and disordering of the γ precipitates is faster than dissolution. As the Al content increases from 20.2 to 20.8 at.% Al, the initial precipitation and growth of γ precipitates decelerates, and the volume fractions of γ precipitates decreases with higher Al content. The rate constants of steady-state coarsening decrease with decreasing volume fraction of γ precipitates, the particle size distributions (PSDs) are broader than the PSDs predicted by Lifshitz–Slyozov–Wagner theory at steady-state coarsening, and the PSD becomes broad with increasing volume fraction of γ precipitates. The simulated morphology and kinetics variation of the γ precipitates are similar to previous experimental results.

Aiming at understanding how intermetallic phases response when AA2024-T3 aluminium alloy is exposed to chloride-containing aqueous medium, scanning electron microscopy was employed to provide morphological information on alloy surface before and after corrosion testing. Energy dispersive X-ray spectroscopy was carried out to determine compositional change in intermetallic particles. Atomic force microscopy was used to examine topographical variation introduced by the reactions of intermetallic phases. Transmission electron microscopy combined with ultramicrotomy was carried out on dealloyed Al2CuMg particles and their periphery region. It is found that dealloyed Al2CuMg particles exhibited porous, polycrystalline structure comprised of body-centred cubic copper particles with sizes of 5 to 20 nm. Aluminium matrix started to trench in the periphery of Al2CuMg particles at the early stage of dealloying. Development of trenching in Al–Cu–Fe–Mn–(Si) particle's periphery was not uniform and took longer time to initiate than Al2CuMg dealloying. Localized corrosion at a cluster of Al2CuMg and Al2Cu particles was mainly associated with Al2CuMg particles.

In order to manifest the influence of specific microstructural component on the development of severe localized corrosion in an AA2099 aluminum–lithium alloy, the corrosion behavior of the alloy subjected to solution heat treatment, cold working and artificial ageing was investigated. Immersion testing and potentiodynamic polarization were employed to introduce localized corrosion; scanning electron microscopy and transmission electron microscopy were used to characterize the alloy microstructure and corrosion morphology. It was found that the susceptibility of the alloy to severe localized corrosion was sensitive to thermomechanical treatments. Additionally, the state of alloying elements influenced the mechanism of localized corrosion propagation. Specifically, the alloy in T8 conditions showed higher susceptibility to severe localized corrosion than that in other conditions. During potentiodynamic polarization, the alloy in solution heat-treated and T3 conditions displayed crystallographic corrosion morphology while the alloy in T6 and T8 conditions exhibited selective attack of grain interiors and grain boundaries in local regions.

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.

One of the main bottleneck issues for room-temperature antiferromagnetic spintronic devices is the small signal read-out owing to the limited anisotropic magnetoresistance in antiferromagnets. However, this could be overcome by either utilizing the Berry-curvature-induced anomalous Hall resistance in noncollinear antiferromagnets or establishing tunnel junction devices based on effective manipulation of antiferromagnetic spins. In this work, we demonstrate the giant piezoelectric strain control of the spin structure and the anomalous Hall resistance in a noncollinear antiferromagnetic metal - D019 hexagonal Mn3Ga. Furthermore, we built tunnel junction devices with a diameter of 200 nm to amplify the maximum tunneling resistance ratio to more than 10% at room-temperature, which thus implies significant potential of noncollinear antiferromagnets for large signal-output and high-density antiferromagnetic spintronic device applications., Comment: 16 pages, 5 figures

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.

Spintronic devices based on antiferromagnetic (AFM) materials hold the promise of fast switching speeds and robustness against magnetic fields. Different device concepts have been predicted and experimentally demonstrated, such as low-temperature AFM tunnel junctions that operate as spin-valves, or room-temperature AFM memory, for which either thermal heating in combination with magnetic fields, or N\'eel spin-orbit torque is used for the information writing process. On the other hand, piezoelectric materials were employed to control magnetism by electric fields in multiferroic heterostructures, which suppresses Joule heating caused by switching currents and may enable low energy-consuming electronic devices. Here, we combine the two material classes to explore changes of the resistance of the high-N\'eel-temperature antiferromagnet MnPt induced by piezoelectric strain. We find two non-volatile resistance states at room temperature and zero electric field, which are stable in magnetic fields up to 60 T. Furthermore, the strain-induced resistance switching process is insensitive to magnetic fields. Integration in a tunnel junction can further amplify the electroresistance. The tunneling anisotropic magnetoresistance reaches ~11.2% at room temperature. Overall, we demonstrate a piezoelectric, strain-controlled AFM memory which is fully operational in strong magnetic fields and has potential for low-energy and high-density memory applications., Comment: 9 pages

T1 (Al2CuLi) phase precipitates, the main strengthening precipitates in third generation aluminum-copper-lithium (Al-Cu-Li) alloys, play a critical role in determining the corrosion behavior of these alloys. Herein, the T1 precipitates, sufficiently large to be visualized by scanning electron microscopy, were intentionally grown in a commercial Al-Cu-Li alloy through a high temperature annealing process. The corrosion and anodizing behavior of the alloy associated with individual T1 precipitate plates was subsequently investigated. It was observed that corrosion initiated instantaneously on T1 precipitate plates when the alloy was exposed to laboratory air. When immersed in NaCl solution, T1 precipitate plates corroded through a dealloying process and then, drove anodic dissolution of the adjacent aluminum alloy matrix by forming copper-rich nanoparticles at the sites of dealloyed T1 precipitates. The T1 phase precipitates were anodized relatively faster than the aluminum matrix in tartaric-sulfuric acid solution under a constant voltage of 14 V. The anodic film formed from T1 precipitates was dissolved quickly by the anodizing electrolyte during anodizing at relatively higher temperatures, resulting in cavities of sizes similar to those of T1 precipitate plates.

A study has been carried out of the effect of an anodizing pre-treatment in a sulphuric acid electrolyte on the strength of AA 5052 alloy/polypropylene joints prepared using friction stir spot welding. Lap-shear tests were used to determine the joint strength. Comparisons were made with joints pre-treated using sand blasting. The failed specimens were examined by scanning and transmission electron microscopy. Anodizing improved the strength of the joints by a factor of about 6 compared with sandblasting. For the anodizing pre-treated joints, melted polymer infiltrated deeply within the nanoporous anodic film, forming a strong polymer-film bond. Joint failure occurred by ductile tearing of the polymer at or near the film surface. In contrast, sandblasted joints failed at the alloy/polymer interface.

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

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.

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 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.

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.

The corrosion susceptibility of dissimilar friction stir welds of AA5083-O and AA6082-T6 alloys has been investigated. Two different tool traverse speeds were compared, revealing that the faster welding speed resulted in increased susceptibility to corrosion because of the reduced tool rotation rate per weld length for heat generation and mixing of materials. The heat affected zones of both alloys and the transition regions between the AA5083-O and the AA6082-T6 rich zones have been identified to be the regions that are most susceptible to corrosion. Grain boundary sensitization in the heat affected zones of both alloys, distribution of Mg 2 Si particles along the boundary between the two alloys (in the thermomechanically affected zones of the welds) and the galvanic interactions between the AA5083 rich zones and the AA6082 rich zones were observed to be responsible for the corrosion susceptibility in the welds.

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.

The scanning vibrating electrode technique has been used to characterize the galvanic interactions between AA2024T3 and mild steel at room temperature and elevated solution temperatures up to 60 °C in naturally aerated 3.5% NaCl solution. The work shows that from a solution temperature of 43 °C and above, highly localised anodic activities with high intensities occur on the mild steel, compared with the anodic activities occurring on the AA2024T3 alloy in a couple system of the two alloys. The highly localised activities on the mild steel were not observed at 34±1 °C with the surface showing no distinct corrosion activities and AA2024T3 alloy was completely the bulk anodic material at this solution temperature. At room temperature, AA2024T3 was also the bulk anode, although mild anodic activities were detected on the surface of the mild steel alloy. The local corrosion activities revealed by the scanning vibrating electrode technique were in agreement with the micrographs of the surfaces of the alloys after the immersion tests.

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.

The anodizing behavior of iron-containing intermetallic particles in AA2099 aluminum-lithium alloy and their effect on structure and corrosion resistance of the anodic film were investigated using electrochemical measurements and scanning electron microscopy. High-copper-containing Al-Fe-Mn-Cu particles (HCCPs) dissolved preferentially through dealloying at ∼ 0 V (vs. saturated calomel electrode) in a tartaric-sulfuric acid solution, at 22, 37 and 42◦C, leading to formation of copper-rich nanoparticle of 50–200 nm diameters. They dissolved completely under normal anodizing conditions, resulting in cavity defects of micrometer dimensions in the anodic film and sunken regions in the alloy substrate immediately beneath the dissolved HCCPs. Immersion testing of the anodized alloy in 3.5% NaCl solution for 24 h indicated that localized corrosion of the anodized alloy predominantly developed at the site containing dissolved HCCPs at the film/alloy interface. It is suggested that HCCPs play a critical role in controlling the corrosion resistance of the anodic film formed on AA2099 aluminum-lithium alloy.

A near-surface layer existed on a cold rolled and annealed foil stock AlFeSi alloy due to severe shear strain during twin-roll casting and subsequent cold rolling. The near-surface layer, with a thickness up to ~ 700 nm and consisting of ultrafine grains with diameters up to 100 nm and high population of voids/microcracks, was present as randomly distributed patches on the alloy surface. The grain boundaries within the near-surface layer were decorated by oxide particles and inclusions of lubricant residue, which reduce the ductility of the near-surface layer. During sheet forming, further shear deformation occurred in the near-surface region due to the friction caused by the sliding contact between the alloy sheet and the forming tool. The differences in the microstructure and the ductility between the near-surface layer and the underlying bulk alloy resulted in cracking within the near-surface layer and/or at the near-surface layer/bulk alloy interface, finally leading to the delamination of patches of the near-surface layer. The delamination generated flake-like alloy debris may significantly modify the property of forming lubricant and influence the tendency to galling during sheet forming.

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.