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Highlights: [•] The Al–Cu alloys modified by RE x O y have superior corrosion resistance than those unmodified alloys. [•] In 3.5wt.% NaCl solution, the corrosion resistance increases with the increasing RE x O y content. [•] In pH=4 acid solution, the corrosion resistance decreases with the increasing RE x O y content. [ABSTRACT FROM AUTHOR]

Combined effects of the cooling rate, alloy composition, and crystal-melt (CM) interfacial anisotropy on solidification of Al-Cu alloys are studied by integrating molecular dynamics and phase-field simulations. Capillary fluctuation method is used to determine the CM interfacial energy properties by molecular dynamics simulations for alloys ranging from 3 to 11 at% Cu. While the average CM interfacial energy decreases with increasing Cu content, its anisotropy does not present a clear trend with composition change. Primary and secondary dendrite arm spacings as well as θ-phase fraction are calculated by phase-field simulations, and validated against experimental measurements and analytical solutions at cooling rates ranging from 1 to 1250 K/s. Results show that the θ-phase fraction decreases with increasing the cooling rate, and this reduction is more drastic in alloys with a higher Cu content. Also, the microstructure features are influenced by the growth dynamics, where seaweed structure formation results in a more homogenous distribution of θ-phase and a finer microstructure. The effects of temperature gradient, Cu concentration gradient, and interfacial energy properties on the dendritic growth morphology of Al-Cu alloys are summarized by a map of supercooling versus the CM interfacial anisotropy to predict pattern formation. The results show that, irrespective of Cu content and cooling rate, the seaweed structure formation is halted at CM interfacial anisotropies larger than 0.005. As the anisotropy decreases, different seaweed structures can form regarding the constitutional supercooling. At low anisotropies (Al-3 and Al-8.4 at% Cu) and low supercooling (Al-3 at% Cu) fractal or degenerate seaweed is dominant while at high supercooling (Al-8.4 at% Cu) compact seaweed forms. This difference in supercooling stems from different solute atom transport rates. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: [•] The effect of Fe-rich phases on squeeze cast Al–Cu alloys with high Fe content. [•] Four kinds of Fe-rich phases may present in Al–Cu alloys. [•] There is great tolerance to Fe impurities in squeeze cast Al–Cu alloys. [ABSTRACT FROM AUTHOR]

ABSTRACT The aim of this work is to show that the presence of a crevice between copper and aluminium and the differential pH values inside and outside the crevice can induce copper dissolution and replating. This was first observed on an assembly between an AA2024 aluminium sheet and a rivet of same composition. The conditions encountered in a crevice were then obtained using a thin-layer electrochemical cell, in which a thin electrolyte layer of 150 µm was trapped between a pure copper and a pure aluminium electrode. A mechanism is suggested involving local acidification in the crevice, due to Al dissolution, pH increase towards the crevice opening and selective dissolution of cuprous oxide at the mouth. Cuprous oxide formation is replenished outside the crevice where oxygen reduction maintains an alkaline interface. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: In this study thin Al–Cu hypoeutectic alloys were mounted in a Bridgman furnace and solidified near isothermally from above the liquidus to below the eutectic temperature. The eutectic transformation is easily identified from the X-ray absorption contrast difference between the semi-solid mush and the fully solid phase in the field of view (FOV). By virtue of real time in situ X-radiography, and subsequent image analysis techniques, it was possible to directly observe and accurately measure eutectic nucleation, as well as transformation rate across the FOV. Post-solidified samples were then subjected to further microstructural analysis, whereby the lamellar eutectic spacings were measured at random locations across the FOV region. The lamellar spacings were correlated with the eutectic transformation rate and showed reasonable agreement with theoretical predictions. Some interesting observations, such as, for example, in situ observations of solidification shrinkage and the effect of liquid feeding through the semi-solid mush, are also discussed. [Copyright &y& Elsevier]

Abstract: Equal channel angular pressing (ECAP) is a material processing method that allows very high strains to be imposed, leading to extreme work hardening and microstructural refinement. Billets of nonhomogenized (as-cast) and homogenized Al–2 and 3wt.%Cu alloys were successfully processed by (ECAP) up to different number of passes at room temperature. The effect of the pre-homogenization treatment before the (ECAP) process on the fracture characteristics and wear properties was investigated. The pre-homogenization treatment has an obvious effect on the fracture mode and fracture surface morphology of the Al–Cu alloys. The homogenized alloys have higher wear resistance than the nonhomogenized alloys. The wear mechanism depends on the sliding distance, applied load and the homogenization treatment. The analysis of the worn surfaces indicates the transfer of higher Fe amount from the rotating disc into the sliding pin in the case of nonhomogenized alloys than that in the case of the homogenized alloys. [Copyright &y& Elsevier]

Abstract: The columnar - to - equiaxed transition (CET) was investigated in Al-Cu alloys (Al-1wt.%Cu, Al-4.5wt.%Cu, Al-15wt.%Cu and Al-33.2wt.%Cu) solidified directionally upward from a chill face. The CET occurs when the temperature gradient in the melt ahead of the columnar front reaches minimum and critical values. Two dimensionless numbers (Ω and Π numbers) that can relate the system parameters (cooling rate, local solidification time and liquidus temperature of the alloy) were defined. The Ω number which shows a linear relationship with the local solidification time and the Π number, that for the Al-rich region in the Al-Cu system, strongly depend on the macrostructure. These results are important to correlate the experimental values of physical quantities, which are relevant to describe the solidification process. [Copyright &y& Elsevier]

Abstract: Equal channel angular pressing (ECAP) is a material processing method that allows very high strains to be imposed, leading to extreme work hardening and microstructural refinement. Billets of nonhomogenized (ascast) and homogenized Al–2 and 3wt.%Cu alloys were successfully processed by ECAP up to different number of passes at room temperature. The microstructure was evaluated into ultrafine grained (UFG) microstructure with high grain boundary misorientation angle in the case of Al–Cu homogenized and nonhomogenized alloys due to imposed strain resulted. It was observed that more homogenized microstructures with smaller grain sizes and higher values of high grain boundary misorientation angle were obtained in the case of homogenized alloys. Higher improvement in the tensile properties and the microhardness values was noted in the case of Al–Cu homogenized alloys. The elongation% and uniform elongation% were observed to decrease with increase of the number of passes for all of the Al–Cu alloys except in the case of Al–3%Cu homogenized alloy. In the case of Al–3wt.%Cu alloy, the elongation% and uniform elongation% were decrease after the second pass then it increases with the addition of more passes. The microhardness distribution and the deformation homogeneity across the transverse direction of the billet were measured. The homogeneity of deformation was observed to increase with the increase of the ECAP number of passes and the copper content. Higher degree of the homogeneity of deformation was observed in the case of the homogenized alloys comparing to that in the case of the nonhomogenized alloys. [Copyright &y& Elsevier]

Abstract: The isothermal and non-isothermal ageing of an Al-2.4wt% Cu alloy have been studied using X-ray diffraction analysis and differential scanning calorimetry (DSC) at different heating rates. Quantitative metallography methods have been applied to measure the corresponding transformed volume fractions at various temperatures and times of precipitation. The variation of the heating rate using DSC technique has allowed us to calculate two kinetics parameters of precipitation which are the Avrami exponent and the activation energy of the process using Kissinger, Ozawa and Bosswell methods. These parameters are similar to those found for the precipitation reaction of θ′ and θ (Al2Cu) phases. [Copyright &y& Elsevier]

Abstract: Semi-solid deformation has been directly observed in an Al–12 wt.% Cu alloy through the combination of real-time synchrotron X-ray radiography and a bespoke high-temperature tensile tester over a range of fraction solid from 0.35 to 0.98. During deformation at low and moderate fraction solids, the X-ray radiographs indicate that there is significant feeding of interdendritic liquid in the region of strain localization prior to crack formation. Furthermore, the measured load required to initiate localized tensile deformation was found to be similar over the range of fraction solid 0.35 to 0.66. At higher fraction solids, the radiographic observations are consistent with classical hot tearing behaviour: limited liquid flow due to low permeability; void nucleation and coalescence; and final failure. Based on these results, a three-stage mechanism for semi-solid failure is proposed which includes the effects of liquid flow and micro-neck formation. [ABSTRACT FROM AUTHOR]

Abstract: Cu additions to Al alloys decrease pitting susceptibility provided that the Cu is retained solid solution. In this study, a range of electrochemical, surface analytical and electron microscopy characterization experiments were carried out with Al–Cu solid solution alloys to understand the origins of this inhibiting effect. Potential-controlled electrochemical polarization experiments carried out in dilute chloride solutions show that stimulation of alloy dissolution without inducing passive film breakdown significantly ennobles a subsequently measured pitting potential. Similar effects are not observed with high-purity Al or Al–Zn solid solution samples. The ennobling effect is more difficult to detect in large area electrodes due to pit initiation triggered by defects and inclusions that are more regularly encountered in larger electrodes. X-ray photoelectron spectroscopy of Al–Cu solid solution samples reveals no Cu enrichment above detection limits. However, scanning transmission electron microscopy and spectral imaging of specially prepared Al–Cu needle-type samples shows that Cu is enriched at the alloy interface by a range of exposure regimens including those that induce pitting. These results suggest the possibility of local Cu enrichment at incipient pit sites by metastable pitting, which can contribute to an ennoblement of the critical pitting potential under certain circumstances. [Copyright &y& Elsevier]

Abstract: This study was undertaken to investigate the machinability aspects of four new Al–Cu casting alloys with regard to the drilling and tapping processes; the base alloy is the 220 Al–2%Cu–1.3%Si–0.4%Mg alloy from which the other three alloys were prepared through the addition of TiB2 and Zr, Sn, and Bi. The machining performance was evaluated based on the calculation of the total cutting force and moment together with that of the tool life expressed as the number of holes drilled/tapped up to the point of tool breakage. The evaluation range was limited by a predefined targeted tool life of 2520 holes corresponding to 14 machinability test blocks. The results show that more than 2520 holes can be drilled for all the alloys studied without drill breakage. The addition of Sn and Bi decreases the total drilling force over the evaluation range by 14% and 25%, respectively, compared to the base alloy. The total drilling moment was reduced by almost the same ratios. All the alloys studied produce a fan-shaped chip which is considered to be the ideal chip for most drilling applications. The addition of Bi increases chip fragility considerably whereas no distinct change in chip characteristics was caused by the addition of Sn. No significant drill wear or any outstanding change in the built-up edge (BUE) to be observed with the progress of the drilling process. A comparative study was also carried out on the machining behavior of these new alloys, represented by their base 220 alloy, with that of the A206, 356, B319, and A319 alloys. Results revealed that the 220 alloy may be proposed as a promising cheaper and lighter alternative for the machining application of the A206 alloy. Furthermore, the machinability of the 220 alloy may be deemed an acceptable compromise between that of the 356 and B319 alloys, on the one hand, and that of the A319 alloy on the other. [ABSTRACT FROM AUTHOR]

Abstract: The pitting corrosion of Al, and two Al–Cu alloys, namely (Al–2.5% Cu) and (Al–7.0% Cu) was investigated in gluconic acid (HG) solution through linear polarization and cyclic voltammetry techniques complemented with ex situ EDX and SEM examinations of the electrode surface. Inductively coupled plasma-atomic emission spectroscopy (ICP-AES) method of chemical analysis was used to study the effect of alloyed Cu on the rate of the uniform corrosion of Al in these solutions. Results obtained from ICP were compared with those obtained from polarization measurements. For the three Al samples, the anodic responses did not involve active/passive transition due to spontaneous passivation. Addition of HG induced pitting (confirmed from SEM) within the passive oxide film due to the aggressive attack of gluconate (G−) anions. Relationships between pitting potential (E pit), HG concentration, temperature, pH and potential scan rate were established. Alloyed Cu was found to enhance uniform corrosion, while it suppressed pitting attack. Local acidification model is employed to explain passivity breakdown induced by pitting corrosion as a result of the aggressive attack of G− anions. [Copyright &y& Elsevier]

Abstract: Equal channel angular pressing (ECAP) is a material processing method that allows very high strains to be imposed, leading to extreme work hardening and microstructural refinement. To investigate the deformation homogeneity in the transverse direction, rigid-viscoplastic 3D finite element simulations were conducted for the different numbers of ECAP passes of Al with Cu contents 0–5%. The simulation results indicated that the material on the outer side of the die channel undergoes less deformation than that in the inner side due to the formation of a corner gap. It was also found that the homogeneity increased with increasing the number of ECAP passes and the copper content due to the decrease in the size of the corner gap. To verify the 3D finite element simulation results, the microhardness homogeneity across the transverse direction of the billet was measured. The same trend was observed: the homogeneity in hardness increased with increasing the number of ECAP passes and Cu contents from 0% to 5%. The homogeneity of deformation indicated by microhardness and by FEM results was higher for route A compared with route Bc and increases with the number of ECAP passes. The homogeneity in route A was higher than that in route Bc by 10% after 2 passes up to 8 passes. [Copyright &y& Elsevier]

Abstract: Using a modified dispensed drop method, a decrease in contact angle on sapphire from pure aluminum to low-copper-containing Al alloys (7–12 wt.%) was found; with higher copper additions θ transitions to the non-wetting regime. Atomic force microscopy on long-term samples showed a significantly increased surface roughness beneath the drop. Using high-resolution transmission electron microscopy, the reaction product at the interface was identified as CuAl2O4 for Al–7Cu and Al2O3 for an Al–99.99 drop. X-ray photoelectron spectroscopy further confirmed the formation of CuAl2O4 under CuAl2 drops. Spinel formation is caused by reaction of the alloy with residual oxygen in the furnace that is transported along the interface as modeled by thermodynamic simulations. The formation of CuAl2O4 causes the reduced σsl and hence the improved wettability of sapphire by low-copper-containing alloys compared to pure aluminum. The main reason for the increase in θ with higher copper contents is the increasing σlv of the alloy. [Copyright &y& Elsevier]

Abstract: The phenomena involved during equiaxed growth, which is the most common growth morphology in metal casting, are dynamic. Therefore, in situ investigation is necessary to fully analyse the microstructure formation. Synchrotron X-ray radiography has become a major tool for in situ characterization of solidification in metallic systems. This paper reports on dedicated equiaxed solidification experiments carried out at the European Synchrotron Radiation Facility (ESRF) in Grenoble-France on Al–10wt.% Cu alloy. The analysis is based on the recorded images obtained through absorption radiography. Equiaxed growth is achieved in nearly isothermal conditions and observed continuously in real time from the early stages of solidification to the final state. The evolution of the dendrite arm lengths and the corresponding growth rates are analysed for two couples of grains in relation with their environment. This analysis suggests that the solutal interaction is dominant between equiaxed grains. [Copyright &y& Elsevier]

Abstract: There is a dearth of published experimental measurements of flow stress behaviour of semi-solids, yet it is critical for simulating phenomena ranging from the processing of metals to the flow of magma. In this paper, a method for calculating flow stress behaviour of semi-solids was developed using a combination of high-temperature compression testing, X-ray microtomography (XMT) imaging and direct finite element modeling (DFEM). This novel methodology was applied to columnar dendritic structures in semi-solid Al–Cu alloys via first quantifying the complex geometry of the semi-solid using XMT. Then these three-dimensional datasets were meshed and their behaviour was simulated using DFEM to derive the stress–strain relationship with a fraction solid (f S ) dependency term. The mechanical behaviour of the solid dendrites near the liquidus temperature was not available in the literature; therefore, samples were fabricated and compression tested using a Gleeble 3500 thermomechanical simulator. The resulting XMT–DFEM-derived constitutive equation predicts the flow stress behaviour of semi-solid in the range of f S equal to 0.1–0.9, showing good correlation to prior experimental data for both other aluminium and ferrous alloys. [Copyright &y& Elsevier]

This paper reports on experiments dedicated to equiaxed solidification carried out on Al — 10 wt% Cu alloy at the European Synchrotron Radiation Facility (ESRF) in Grenoble-France. Equiaxed growth was achieved in nearly isothermal conditions and observed continuously in real time from the early stages of solidification to the developed grain structure by X — ray radiography. The length of primary dendrite arms was measured on several growing equiaxed grains as a function of time and it was found that dendrite arm evolution can be well fitted by the Kolmogorov — Johnson — Mehl — Avrami ( KJMA) function. The growth of four primary dendrite arms of a single grain was then characterized. The dendrite arms behaved differently depending on their growth directions and the presence of grains in their vicinities. At the beginning, the dendrite arm directed upwards was growing faster than the ones growing below because of “self — poisoning” due to a gravity driven fluid flow. In the late stage of solidification, analysis on several couples of grains growing towards each other confirmed that solutal interaction was the main cause of growth being stopped. [ABSTRACT FROM AUTHOR]

Abstract: Creep behavior of the unmodified and modified cast Al–Cu alloys was investigated at temperatures from 393 to 483K in the tension test. The creep resistance ability of the Al–Cu alloy modified by Pr x O y is almost 3–5 times as high as that of the unmodified Al–Cu alloy, which is attributed to a large number of nano-scale θ′ precipitates with high thermal stability in the modified Al–Cu alloy restricting and impeding the dislocation movement during the creep. The induction of a threshold stress in the analysis leads to a stress exponent of 5, which suggests that the creep behavior of both the present alloys is associated with the lattice diffusion-controlled dislocation climb (n =5). [Copyright &y& Elsevier]

Polarization measurements were employed, as a first step towards studying the corrosion behaviour of Al and two Al–Cu alloys, namely Al–4.5%Cu, and Al–7.5%Cu alloys in deaerated stirred 1.0 M H3PO4 solution at 25 °C. Inhibition of Al and Al–Cu alloys corrosion in 1.0 M H3PO4 solution, using sodium oleate (SO) as an anionic surfactant inhibitor, was also studied. Polarization curves showed that SO acted as a mixed-type inhibitor to Al corrosion, while it acted mainly as a cathodic inhibitor to the acid corrosion of Al–4.5%Cu, and Al–7.5%Cu alloys. Inhibition is accomplished by inhibitor adsorption on the electrode surface without detectable changes in the chemistry of corrosion. The relationship between surfactant concentration, surfactant critical micellar concentration (CMC), and corrosion inhibition is also discussed based on the Langmuir isotherm assumption, commonly applied in corrosion inhibition evaluations. The protection efficiency increases with increase in surfactant concentration and %Cu in Al samples. Maximum protection efficiency of the surfactant is observed at concentrations around its CMC. The mechanism of adsorption is discussed based on the surface charge of the electrode surface. [ABSTRACT FROM AUTHOR]

Tensile and compressive creep tests were performed at 300 °C on high-temperature Al–Cu–Mn–Zr (ACMZ) alloys with 6 wt% Cu (6Cu) and 9 wt% Cu (9Cu) to evaluate the effect on creep properties of micron-size θ-Al 2 Cu intergranular precipitates. For compressive creep, the increased volume fraction of θ-precipitates at grain boundaries (from ∼0.7% in 6Cu to ∼ 6% in 9Cu) does not affect deformation rates across the investigated stress range of 15–110 MPa, consistent with creep being controlled by submicron θ′-Al 2 Cu precipitates within grains, whose size and fractions are the same in both alloys. In contrast, for tensile creep, 9Cu creeps faster than 6Cu at stresses above 20 MPa, and this difference increases with the stress level. This discrepancy between tensile and compressive creep behavior is explained by cavitation during tensile creep, which is favored by higher volume fraction and larger size of intergranular θ precipitates in 9Cu. Conversely, larger precipitates impede cavity linkage resulting in improved creep ductility of 9Cu as compared to 6Cu at 300 °C. [ABSTRACT FROM AUTHOR]

Abstract: Non-isothermal ageing of an Al–4, 5% Cu alloy has been studied by using differential dilatometry, differential scanning calorimetry (DSC) and high-temperature X-ray diffraction (HTXRD). Six anomalies have been detected on the differential thermodilatometry curve (DTD). The GP zones formation and dissolution are traduced by two small contractions followed by one expansion. The precipitation of θ′-phase induces a big expansion and its dissolution reaction produces an important contraction. Moreover, θ-phase formation accompanies the precipitation, as well as the dissolution reactions of the θ′-phase. The θ-phase dissolution which dissolves the Cu atoms in the Al lattice is accompanied by a thermal dilatation of the Al lattice. The obtained values of the activation energy associated to the main precipitation reaction, by using Kissinger and Ozawa methods, are similar to that found for the precipitation reaction of θ′-phase. [Copyright &y& Elsevier]

Pre-stretching prior to ageing in Al-Cu alloys leads to preferential formation of precipitates in certain habit planes and produces anisotropic mechanical properties. In this work, we attempt to eliminate this problematic anisotropy by adding Sc and Zr to an Al-Cu alloy. When pre-stretching the binary Al-Cu alloy along the [001] Al zone axis, transmission electron microscopy (TEM) reveals that precipitation of θ ″ occurs mostly on the (001) Al plane (and not on the (100) Al and (010) Al planes). This "stress orienting effect" is caused by the local change in elastic strain energy induced by the pre-stretching. In the pre-stretched Al-Cu-Sc-Zr alloy, the presence of coherent Al 3 (Sc, Zr) dispersoids is found to promote equivalent nucleation of θ ′ precipitates in all three habit planes (at the expense of θ ″), resulting an isotropic precipitate distribution. The strengthening potential of these different precipitate distributions is analytically modelled and discussed. [Display omitted] [ABSTRACT FROM AUTHOR]

Corrosion behavior of the casting Al-Cu alloys with and without Sc addition was studied by both the immersion test and electrochemical measurement methods. The results show that pitting corrosion was found on the surfaces of these alloys in 3.5wt.% NaCl solution, while the corrosion resistance of the Al-Cu alloys with Sc is better than that of the Al-Cu alloy without Sc. With increasing Sc content, the corrosion resistance of the present Al-Cu alloys varies significantly, and the 0.1wt.% Sc alloy has the best corrosion resistance. Also, the corrosion potential of the present alloys with Sc is shifted positively compared with that of the alloy without Sc by electrochemical measurement, indicating that the alloys with Sc have better corrosion resistance. The microstructures of the Al-Cu alloys change from the coarse grains to the fine equiaxed grains due to Sc addition, which is responsible for the reduced susceptibility to corrosion and the enhanced corrosion resistance of the present alloys. [ABSTRACT FROM AUTHOR]

Abstract: A comparative study on the work hardening of Al–Mg and Al–Cu alloys was carried out using a Kocks–Mecking–Estrin type analysis of stress–strain curves obtained in tension tests at constant loading rate. As a result of the analysis, dependencies of forest dislocation storage and dynamic recovery rates on the Mg and Cu concentration have been derived. The work hardening behavior and the microstructure formation in the Al–Mg and Al–Cu alloys were shown to be similar despite the opposite effects of Cu and Mg on stacking fault energy as well as the differences in solute atom size and friction stress. The influence of alloying on the work hardening peculiarities and the dislocation substructure evolution was discussed in connection with the effects of solute–dislocation interaction. [Copyright &y& Elsevier]

Abstract: The plane strain fracture toughness, and crack growth toughness in terms of the non-dimensional tearing modulus, T R of Al–Cu alloy were evaluated following the J-integral method. An empirical relation is proposed for estimating the fracture toughness from the tensile properties. The estimated fracture toughness values from the empirical relation are found to be in good agreement with the measured fracture data. The microstructural as well as strength variations in the subject alloy were examined through different aging treatments (viz., under aging (UA), natural aging (NA), peak aging (PA) and over aging (OA)). The microstructural observations in different aging conditions were made through transmission electron microscopy (TEM) to understand the type of phase or intermediate stages of the phase present (GP zones, θ″, θ′ or θ). Fracture toughness testing has been carried out on 14mm thick compact tension (CT) specimens and estimated the crack extension by unloading compliance technique. It was noted that the yield strength increases and fracture toughness decreases with the increase in the degree of aging from NA to PA condition. On overaging the alloy to a yield strength level as that of UA, it was not possible to retain the UA level of fracture toughness. The highest crack growth toughness is exhibited by the NA temper. The fractography analysis revealed that the fracture mode was predominantly transgranular dimpled rupture. Fracture initiation occurred by void nucleation at the second phase particles. The differences in the fracture toughness of the alloy in different aging conditions were shown to be dependent on the differences in the matrix deformation behavior and the strength differential. [Copyright &y& Elsevier]

Abstract: The influence of various concentrations of NaClO4, as a pitting corrosion agent, on the corrosion behaviour of pure Al, and two Al–Cu alloys, namely (Al+2.5wt% Cu) and (Al+7wt% Cu) alloys in 1.0M Na2SO4 solution was investigated by potentiodynamic polarization and potentiostatic techniques at 25°C. Measurements were conducted under the influence of various experimental conditions, complemented by ex situ energy dispersive X-ray (EDX) and scanning electron microscopy (SEM) examinations of the electrode surface. In free perchlorate sulphate solutions, for the three Al samples, the anodic polarization exhibits an active/passive transition. The active dissolution region involves an anodic peak (peak A) which is assigned to the formation of Al2O3 passive film on the electrode surface. The passive region extends up to 1500mV with almost constant current density (j pass) without exhibiting a critical breakdown potential or showing any evidence of pitting attack. For the three Al samples, addition of ClO4 − ions to the sulphate solution stimulates their active anodic dissolution and tends to induce pitting corrosion within the oxide passive region. Pitting corrosion was confirmed by SEM examination of the electrode surface. The pitting potential decreases with increasing ClO4 − ion concentration indicating a decrease in pitting corrosion resistance. The susceptibility of the three Al samples towards pitting corrosion decreases in the order: Al>(Al+2.5wt% Cu) alloy>(Al+7wt% Cu) alloy. Potentiostatic measurements showed that the rate of pitting initiation increases with increasing ClO4 − ion concentration and applied step anodic potential, while it decreases with increasing %Cu in the Al samples. The inhibitive effect of SO4 2− ions was also discussed. [Copyright &y& Elsevier]

Abstract: The enrichment of copper alloying additions near the surface of sputtering-deposited Al–1.3at.%Cu, Al–2.7at.%Cu and Al–30at.%Cu alloys is investigated following immersion in nitric acid, which is used commercially as a de-smutting pre-treatment. Corrosion of the alloys is revealed at rates in the range 4–13nmmin−1, leading to enrichment of copper in the alloy surface regions. Enrichments are also generated by nitric acid treatment of AA2024-T3 and AA7075-T6 alloys, with levels similar to those achieved by etching in sodium hydroxide solution. Conventional durations of de-smutting treatments in nitric acid have minor influences on the magnitude of enrichment. [Copyright &y& Elsevier]

Abstract: The influence of heat treatment on the mechanical properties and texture of extruded Al–4.5wt.% Cu alloy in the semisolid state was investigated, and its characteristics were compared with hot extruded Al–Cu alloy. The age hardening characteristics of the semisolid extruded Al–Cu alloy did not show a discernable change compared to the hot extruded. The tensile strength of semisolid extruded Al–Cu alloy was slightly higher than that of the hot extruded Al–Cu alloy, and the difference in their mechanical properties was increased after T6 treatment. The double fiber texture was developed in the hot extruded Al–Cu alloy bar. However, the specific texture in the semisolid extruded Al–Cu alloy was developed in the center with a tilt angle of 50°. This specific texture and equiaxed microstructure indicate that the deformation behavior of the semisolid extrusion was different from that of the conventional hot extrusion. [Copyright &y& Elsevier]

Abstract: Al–Cu alloys castings can exhibit different corrosion responses at different locations due to copper content and to the resulting differences on microstructural features and on Al2Cu fractions. The aim of this study was to investigate the influence of Al2Cu intermetallic particles associated to the dendritic arm spacings on the general corrosion resistance of three different hypoeutectic Al–Cu alloys samples in sulfuric acid solution. The cast samples were produced using a non-consumable tungsten electrode furnace with a water-cooled copper hearth under argon atmosphere. The typical microstructural pattern was examined by using electronic microscopy techniques. In order to evaluate the surface corrosion behavior of such Al–Cu alloys, corrosion tests were performed in a 0.5M sulfuric acid solution at 25°C by using an electrochemical impedance spectroscopy (EIS) technique and potentiodynamic polarization curves. An equivalent circuit was also used to provide quantitative support for the discussions and understanding of the corrosion behavior. It was found that Al2Cu has a less noble corrosion potential than that of the Al-rich phase. Despite that, dendrite fineness has proved to be more influent on corrosion resistance than the increase on alloy copper content with the consequent increase on Al2Cu fraction. [Copyright &y& Elsevier]

Abstract: The wetting behavior and the interfacial reactions that occurred between molten Al–Cu alloys (1, 4, 8, 20, 33, and 100 wt% Cu) and solid TiC substrates were studied by the sessile drop technique in the temperature range of 800–1130 °C. The effect of wetting behavior on the interfacial reaction layer was studied. All the Al–Cu alloys react with TiC at the interface forming an extensive reaction layer. The interface thickness varied with the samples, and depends on the temperature, chemical composition of the alloy and the time of the test. Wetting increases with increasing concentration of copper in the Al–Cu alloy at 800 and 900 °C. In contrast, at higher temperature such as 1000 °C wetting decreases with increasing copper content. The spreading kinetics and the work of adhesion were evaluated. The high values of activation energies indicated that spreading is not a simple viscosity controlled phenomenon but is a chemical reaction process. The spreading of the aluminum drop is observed to occur according to the formation of Al4C3, CuAl2O4, CuAl2, TiCu x mainly, leading to a decreases in the contact angle. As the contact angle decreases the work of adhesion increases with increasing temperature. Al–Cu/TiC assemblies showed cohesive fracture corresponding to a strong interface. However, using pure Cu the adhesion work is poor, and the percentage of cohesion work is also too low (27–34%). [Copyright &y& Elsevier]

Abstract: In theoretical analyses and computational simulations chemical free energies of stoichiometric compounds and solid solution phases are often approximated by parabolic functions. In the present work, we focus on examining the effect of different approximations of chemical free energies on predicted precipitate growth kinetics with phase-field modelling. As an example, we studied the precipitation of plate-like in Al–4 wt%Cu Alloys. Using six sets of chemical free energies for and Al–Cu solid solution, growth kinetics of precipitates were simulated by assuming either constant diffusivity or constant atomic mobility. It is demonstrated that the parabolic function provides a good description for the chemical free energy of a stoichiometric compound while the growth kinetics is sensitive to the approximation of chemical free energy for the solution phase. [Copyright &y& Elsevier]

Cold rolling and hot rolling of solution treated Al–3·7Cu and Al–3·8Cu–1·8Mg alloys were performed to test the effect of inhomogeneous precipitation in shear bands during following aging of the material. The most effective inhomogeneous distribution of particles was observed for samples hot deformed and aged within the temperature range 473–573 K. It was noted that magnesium addition intensifies coarse shear bands development and following coarsening of particles within sheared area. [ABSTRACT FROM AUTHOR]

Abstract: A combined theoretical and experimental approach was undertaken to quantitatively determine thermal variables during solidification, i.e., transient metal/mold heat transfer coefficients, cooling rates and a driving force factor for the solidified shell distortion, given by the gradient of the cooling rate. Such thermal variables were correlated with the geometric features of the observed surface marks of Al–Cu alloys ingots in the range of pure Al and the eutectic composition. It was shown that the thermal distortion factor increases with alloy Cu content, and it is strongly dependent on the initial values of the metal/mold heat transfer coefficient. A correlation with the resulting experimental surface marks has indicated that larger depth and pitch are associated with higher thermal distortion driving forces. [Copyright &y& Elsevier]

Abstract: For rapid chilling, the cast surface will often exhibit a particular group of defects characterized by ripples and laps. This work was carried out to experimentally investigate the influences of alloy solute content, melt superheat, transient metal/mold heat transfer coefficient and teeming speed on the surface quality of Al–Cu alloys ingots in the range of pure Al and the eutectic composition. The surface quality was shown to be enhanced by the increase of melt superheat and of teeming speed and the decrease of the metal/mold heat transfer efficiency. It was shown that the best surface quality is associated with a Cu content close to the maximum solidification range at about 5wt.% Cu. [Copyright &y& Elsevier]

Abstract: Tensile strength, elongation, static toughness and fracture modes of casting Al–0.63wt.% Cu and Al–3.9wt.% Cu alloys subjected to equal channel angular pressing (ECAP) were investigated. It is found that the grains of the two alloys can be refined to submicron level after four passes of ECAP. In addition, precipitation phase θ along grain boundaries in the Al–3.9wt.% Cu alloy was also broken after ECAP treatment. The tensile fracture strength increases with increasing ECAP pass for both of the Al–Cu alloys, however, the elongation is almost independent of the ECAP pass. Consequently, the static toughness of the Al–Cu alloys is enhanced at high ECAP pass. The failure modes of Al–0.63wt.% Cu alloy consist of necking and shear fracture, however, Al–3.9wt.% Cu alloy displays normal fracture and shear fracture with different shear angle. Based on the results above, the tensile properties and failure modes of the Al–Cu alloys are discussed. [Copyright &y& Elsevier]

Abstract: It is generally accepted that laser surface melting (LSM) can be used for improving the corrosion resistance of metallic alloys as a result of homogenization/refinement of microstructure, dissolution/redistribution of precipitates or inclusions and phase transformation. However, some studies have shown that laser-treated surfaces do not always exhibit enhanced corrosion performance. To date, no satisfactory explanation has been given for the findings, in particular concerning the relationship between microstructure and electrochemical responses. This paper summarises the results of the investigations into the corrosion performance of various laser-melted metallic alloys, including AA 2014-T6 and AA 2024-T351 aluminium alloys, AISI 304L austenitic stainless steel and 3CR12 dual-phase steel, to enhance the knowledge of important, but poorly understood relationships between corrosion and microstructural characteristics of surfaces following laser treatment. It has been found that apart from the refinement/homogenization of microstructure, other factors, such as the electrochemical nature of various intermetallics with respect to the solid solution matrix and heat-affected zones produced by overlapping, and phase transformation determined by cooling rate, play key roles in corrosion behaviour after the laser treatment. [Copyright &y& Elsevier]

An Al-Cu alloy (corresponding to the 2014 series) is used to make a composite by the addition of 15 wt% SiC dispersoids adopting the liquid metallurgy route by stir casting. The alloy and the composite are subjected to solutionizing and aging to optimize the attainable properties. They are characterized for their physical, microstructural, hardness, tensile, dry sliding, and abrasive wear (under high stress conditions) properties under identical experimental conditions. The obtained results indicate that the formation of the composite does not always improve the properties. A clear distinction can be made between the properties of alloys which can be improved by the formation of a composite. In other cases, the formation of a composite has resulted in deteriorating the properties of the alloy. The present study analyzes the causes for the behavior exhibited by the alloy and the composite and attempts to lay down conditions under which composites can be successfully used over their counterpart alloys and vice versa. [ABSTRACT FROM AUTHOR]

Abstract: Melt-extrusion is a new fabrication process with the characteristics of both casting and extrusion. In this process, a metallic melt which is poured and solidified up to semisolid state in the container can be directly extruded through the die exit to form a product of bar shape without other intermediate processes. In this study, the fabrication characteristics of the process were evaluated with various process parameters, such as extrusion temperature, initial ram velocity and initial microstructure. Al-Cu alloys were successfully extruded after squeezing out of liquid during melt-extrusion with smaller force compared to the solid extrusion. The extrusion temperature and initial ram velocity increase with increasing volume of squeezed liquid. The extrusion pressure tended toward decrease with increasing extrusion temperature and decreasing initial ram velocity. The amount of squeezed liquid was reduced by treatment of grain refiner into Al-Cu melt. [Copyright &y& Elsevier]

Abstract: Sputter-deposited Al–2at.%Cu layers have been investigated with respect to their microstructure and the spatial distribution of the elements using the tomographic atom probe. Al grains show columnar shape in the as-sputtered state, where the matrix is supersaturated with Cu. Upon annealing at temperatures between 150 and 350°C, a significant decrease in the average Cu concentration is measured within the grains. Neither second phase formation within the Al matrix nor Cu enrichment at the surface or at the layer/substrate interface have been detected, suggesting segregation of Cu atoms in Al grain boundaries. [Copyright &y& Elsevier]

The dendritic spacings are important microstructural parameters involved in solidification processes. They can affect not only microsegregation profiles but also the formation of secondary phases within interdendritic regions, which influences mechanical properties of cast structures. A small number of studies have been carried out in order to analyze the effects of melt convection within the interdendritic region or to verify the influence of growth direction in the dendritic arm spacings. In this work, a combined theoretical and experimental approach is developed to quantitatively determine solidification thermal variables such as transient metal/mold heat transfer coefficients, tip growth rates, thermal gradients, tip cooling rates and local solidification time during downward unsteady-state solidification of hypoeutectic Al–Cu alloys. These solidification thermal variables are correlated with dendritic spacings, which have been measured along cross and longitudinal sections of ingots solidified under downward unsteady-state heat-flow conditions. Predictive theoretical models for dendritic spacings have been compared with experimental observations. A comparison between upward and downward unsteady-state results for dendritic spacings has also been conducted. [Copyright &y& Elsevier]

There is a direct relationship between grain size obtained from macrostructure characterisation and the globule size and shape factor, obtained from microstructure characterisation: the smaller the grain size, the smaller the globule size and shape factor. Due to this a rheocast quality index (RQI=globule size/(grain size×shape factor)) was used to evaluate the Al–4.5 wt.% Cu alloy produced by strain induced melting activation (SIMA). The structure that presents the smallest grain size, the smallest shape factor, and the most homogeneous and globular size of the primary phase, has the best RQI and consequently the best behaviour in the semi-solid forming. Four different as-cast structures were cold rolled to obtain 20 and 40% deformation and were partially melted at 635 °C at holding times of 5 min. Both, macro- and microstructure were characterised. [Copyright &y& Elsevier]

Surface treatments, including chemical polishing, alkaline etching, acid pickling, and electropolishing, of aluminium and copper-containing aluminium alloys lead to enrichment of solid solution copper in the metal just beneath the residual oxide films of the treatment processes. The paper presents the enrichment factor for copper as a function of the copper content of the bulk matrix material. The factor is defined as the ratio of the copper enrichment, measured in units of 1015 atoms cm−2, to the copper content of the matrix in at.%. Although absolute levels of enrichment increase with increase in copper content of the alloy, the enrichment factor increases in the opposite sense. [Copyright &y& Elsevier]

Macrosegregation in metal casting can be caused by thermal and solutal melt convection, and the transport of unattached solid crystals. These free grains can be a result of, for example, nucleation in the bulk liquid or dendrite fragmentation. In an effort to develop a comprehensive numerical model for the casting of alloys, an experimental study has been conducted to generate benchmark data with which such a solidification model could be tested. The specific goal of the experiments was to examine equiaxed solidification in situations where sinking of grains is (and is not) expected. The objectives were: (1) experimentally study the effects of solid transport and thermosolutal convection on macrosegregation and grain size distribution patterns; and (2) provide a complete set of controlled thermal boundary conditions, temperature data, segregation data, and grain size data, to validate numerical codes. The alloys used were Al–1wt.%–Cu, and Al–10wt.%–Cu with various amounts of the grain refiner TiB2 added. Cylindrical samples were either cooled from the top, or the bottom. Several trends in the data are apparent and provide good starting points for comparisons to numerical models. [Copyright &y& Elsevier]

The rheological behavior at high solid fractions of a partially solidified Al–8 wt.% Cu alloy is investigated using shear tests in a Couette viscometer. The effect of grain refinement on the rheological behavior is particularly addressed. Shear experiments have been conducted at three temperatures above the eutectic: 550, 575 and 587 °C. Experimental data reveal a clear difference in the shear response of the refined and unrefined alloys. The grain-refined Al–Cu alloy exhibits a quite homogeneous deformation behavior that can be related to the rheology of the viscoplastic solid phase, which is investigated through simple compression tests. On the contrary, rapid strain localization characterizes the shear response of the non grain-refined alloy. The difference in rheological behavior is related to microstructure features that are pertinent to the rheology of partially solidified alloys, solid phase morphology and grain size. [Copyright &y& Elsevier]

Directional solidification experiments have been carried out on different Al–Cu alloys as a function of solidification parameters, temperature gradient G, growth rate V, and composition C0. The specimens were solidified under steady state conditions with a constant temperature gradient (7.4 K mm−1) at a wide range of growth rates (9–490 μm s−1) and with a constant growth rate of 9.5 μm s−1 at a wide range of temperature gradients (1.0–7.4 K mm−1). Microstructural parameters, the primary dendrite arm spacing λ1, secondary dendrite arm spacing λ2, dendrite tip radius R, mushy zone depth d were measured and expressed as functions of solidification parameters, G, V and C0 by using a linear regression analysis. The results were in good agreement with previous experimental work and current theoretical models suggested for dendritic growth. [Copyright &y& Elsevier]