Pure Aluminum Surface Research Articles

Effects of graphene content in alkaline silicate electrolyte on AA1060 pure aluminum micro‐arc oxidation coating

AbstractCeramic coatings were obtained by micro‐arc oxidation (MAO) on the surface of AA1060 pure aluminum in alkaline silicate electrolyte with the addition of graphene. The effects of graphene contents in the range of 0–.30 g/L in the electrolyte on surface morphology, corrosion resistance, and wear resistance of the ceramic coatings were investigated. The outer surface structure, outer surface element content, coating cross‐section structure, coating cross‐section element content, coating/substrate interface structure, and coating phase were characterized by scanning electron microscope and X‐ray diffraction. Potentiodynamic polarization and electrochemical impedance spectroscopy were used to evaluate the corrosion behavior of MAO samples in a 3.5‐wt% NaCl solution. In addition, the resistance to sliding and abrasive wear of the oxide coating were studied experimentally. The results show that the alkaline silicate electrolyte with the addition of graphene has a significant effect on the characteristics of MAO coating. The performance of micro‐arc oxide coatings is best when the graphene content in the electrolyte is .15 g/L, the average thickness of the film is 7.24 μm, the average pore size is 6.07 μm, the impedance value is approximately 4.01 × 106 Ω, and its friction coefficient is .55.

Numerical erosion prediction of aluminum induced by cavitating jet using an Eulerian–Lagrangian method

Cavitation-induced erosion in pump machinery is a significant issue that leads to material loss and increased operating costs. This study develops a numerical method based on an energy balance approach to address the risk of cavitation erosion. Compared with other published methods, three improvements are made. Firstly, it assumes that the local instantaneous pressure is the driving force behind cavity collapse, rather than the far-away ambient pressure field. Secondly, it counts erosion only at the moment that the released shock wave is strong enough to cause surface damage. Thirdly, an Eulerian–Lagrangian method is introduced to simulate multiscale cavitation, in which the volume of fluid (VOF) method and a discrete bubble model (DBM) are combined to reproduce resolvable water-vapor interfaces and unresolvable discrete bubbles, respectively. The developed numerical modeling framework is validated by predicting the erosion of pure aluminum surface caused by a cavitating jet, and it is shown that the simulated erosion region fits well against the experimental results. Additionally, appropriate model coefficients of the erosion prediction method are introduced to achieve quantitative prediction of material mass loss, and the detailed erosion behavior is discussed.

Fluoride Ions Effect on the Corrosion Behavior of Pure Aluminum in Deaerated 0.05 M Sulfuric Acid Solutions

AbstractThe corrosion study of aluminum‐based materials is the topic of a great scientific attention because of increasing the applications in many sectors of these materials. The fluoride ions (F−) effect on the corrosion behavior of pure aluminum in deaerated 0.05 M sulfuric acid (H2SO4) solutions at 25 °C was investigated. The electrochemical measurements such as open circuit potential and potentiodynamic polarization were accomplished to study the effect of fluoride and sulfate ions present in the test solutions. The optical microscopic and atomic force microscopic images were taken to view the morphologies and surface roughness of pure aluminum which coincidence with the corrosion rates found from the immersion of the test specimens using weight loss method. The surface morphology and elemental compositions of pure aluminum was evaluated by scanning electron microscope and energy dispersive X‐ray spectroscopy, respectively. The results showed that the general corrosion was formed on the surface of pure aluminum. It is also revealed that the surface roughness and amount of corrosion of pure aluminum were increased by the presence of even a very small amount of fluoride ions in deaerated sulfuric acid solutions.

Improving the wear resistance of aluminum by a nickel-filled anodized porous alumina layer

Anodizing is a widely used method for increasing the wear and corrosion resistance of aluminum alloys. However, it is known that the porous brittle alumina layer can easily crack during tribological stresses, which results in the detachment of large particles from the worn surface. Electroplating, on the other hand, can produce a compact ductile metallic coating with enough wear resistance, though a specific pretreatment like the zincate process is needed for an aluminum substrate. In this paper, a combination of the two methods, anodizing and electroplating, is applied on the surface of pure aluminum intending to improve the wear resistance. Anodizing was performed in oxalic acid by applying a constant current density of 2 A/dm2. The anodized samples were then immersed in phosphoric acid for up to 10 h to increase the diameter of the pores. Nickel electroplating was carried out on the anodized samples at a current density of 0.5 A/dm2 in a Watts solution. Cross-sectional studies show that there is an optimum pore widening time that establishes a good adhesion between nickel and anodic oxide layers, while the structure of the oxide film is largely preserved. Sliding wear tests were performed on the samples using a ball-on-disk reciprocating tribometer. The results show much higher wear life for all Ni/Al2O3 composite coatings as compared with the alumina layer. The maximum wear life was obtained for the sample etched for an optimum pore widening time of 4 h.

Preparation and properties of wear‐resistant carbonized‐ceramic composite coating on pure aluminum surface

AbstractIn this paper, a new composite coating was prepared on the surface of pure aluminum (Al) by combining the micro‐arc oxidation (MAO) technology with the polyethylene glycol (PEG 400) carbonization technology. The composite coating and the single MAO coating were observed by a scanning electron microscope, and an energy‐dispersive spectrometer, finding that the single MAO coating surface with volcano‐like pores and microcracks, was covered by the carbonized layer of the composite coating where the overall coating thickness was around 19.5 µm, including 17.5 µm of inner MAO coating. The material properties of the composite coating were characterized by X‐ray diffraction and X‐ray photoelectron spectroscopy. The wear resistance of the composite coating was tested under dry friction conditions, finding that the wear width on the composite coating surface was 909.6 µm only, which was around 55.7%, 50.4%, and 58.2% of those for pure Al substrate, single carbonized coating, and single MAO coating, respectively. Then the comprehensive wear resistance of the composite coating was explored under different sliding speeds and lubrication mediums. Finally, the wear‐resisting mechanism of the composite coating was discussed, concluding that the composite coating could effectively reduce adhesive wear and abrasive wear of the Al substrate.

The effect of adding polyethylene glycol to electrolyte solution on micro-arc oxidation coating on pure aluminum

Micro-arc oxidation (MAO) is a surface treatment technology that enhances the performance of metal surfaces by growing ceramic layers on the valve metal surface to meet the demand of the application. This paper aims to improve the performance of ceramic coatings on pure aluminum surfaces by varying the concentration of polyethylene glycol (PEG) in electrolytes. As an active agent, the PEG extends the ionic activity, and the increasing rate of ion migration in electrolytes improves the reaction rate. And the PEG long chain is also beneficial to electron conduction, which will promote the discharge effect in the MAO process. The MAO coating was characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), the wear resistance of MAO coating was evaluated by tribological experiments, and the corrosion resistance of MAO coating was evaluated by the Neutral salt spray test (NSST). The experimental results showed that the MAO coating had the best wear resistance when the concentration of PEG was 2 g/L. The coatings prepared by adding PEG to the electrolyte have good wear and corrosion resistance, which enhance the service life and application range of the metal and are expected to promote the development of valve metal in application fields.

Cast Aluminum Surface Reinforced with Carbon Nanotube via Solubilization Treatment

Carbon nanotubes (CNTs) are noteworthy, as they reinforce the metallic matrix, due to mechanical properties, such as the ~ 1.0 TPa Young module. To improve the maintenance of the commercially pure aluminum surface, multi-walled carbon nanotubes were incorporated into the aluminum surface with heat treatment by solid solubilization, in order to improve the surface properties of aluminum. The aluminum samples were chemically attacked for 30, 60 and 120 s and placed in a container with CNTs, being subjected to a temperature of 640 °C for 1 h. Then, the roughness was evaluated by a roughness meter for morphology in the scanning electron microscopy. An intensity of aggregation of CNTs was evaluated by XRD, and the Raman Spectra has evaluated the transfer of charge to the matrix. Microhardness was performed to evaluate the influence of the incorporation of CNTs in the matrix. The results obtained show that the incorporation of CNTs in the aluminum matrix increases the hardness in approximately 20% of the surface, in comparison with the control sample. The process of incorporating CNTs into the aluminum matrix by solubilization is a promising, simple and inexpensive alternative to improve the durability of the aluminum surface.

The Effects of UV on the Corrosion Behavior of Pure Aluminum 1060 in Simulated Nansha Marine Atmosphere

The corrosion behavior of pure aluminum 1060 subjected to wet-dry cyclic accelerated test in simulated Nansha marine atmosphere in the dark and UV illumination were investigated by means of scanning electron microscopy, electrochemical impedance spectroscopy and Mott–Schottky measurements in this work. The results showed that the native oxide film is constantly destroyed during the corrosion test in both conditions. Besides, UV illumination can diminish the corrosion attack of the native oxide film to an extent in terms of a photo-induced modification of the native oxide film formed on the pure aluminum surface. In particular, UV illumination can also reduce the carrier concentration in the oxide film, thus reducing the conductivity and the corrosion rate.

Investigation on the Evolution of Subsequent Yield Surface of Pure Aluminum Under Changing Loading Paths Considering Microstructure Effects

The anisotropy behavior is one of the most important key issues in the simulation of sheet metal forming, which can highly affect the prediction accuracy of metal forming behavior, especially under complex loading paths. In this study, the initial and subsequent yield surfaces of the pure aluminum material are numerically investigated through the representative volume element (RVE) methodology. The crystal plasticity theory is chosen to represent the microscopic elastoplastic behavior of pure aluminum, and its polycrystalline geometrical model is built by the Voronoi algorithm. Together with user material subroutine, the initial and subsequent yield surfaces evolution of pure aluminum under different loading paths is simulated in commercial software ABAQUS/Implicit. Through the investigation, the great influence of the microtexture on the obtained inhomogeneous stress distribution of RVE model can be presented. Meanwhile, the effect of the loading directions and the predeformation is also investigated and discussed. The shape of the subsequent yield surface is also strongly dependent on both the yield definition and direction of preloading, and the high anisotropy phenomena appear corresponding to different yield definitions. At the same time, the pole figures at different forming stages are given, and the evolution of polycrystalline texture is analyzed and predicted. It can be concluded that some strong relationship between the texture evolution, the inhomogeneous stress field, and the subsequent yield surface evolution is proved and discussed. This study provides a good methodology to study the yield surface evolution of aluminum together with the crystal plasticity theory, with considering the evolution of the microtexture evolution during the plastic deformation of the metal.

Experimental Study on the Surface Modification by Electrical Discharge Process

The creation of modified layer on metal surfaces using new methods is one of the procedures in surface engineering which can improve the surface mechanical properties. The electrical discharge process is a new method that can form a modified layer on the metal surfaces. This study aims to improve of pure aluminum surface properties through Electrical Discharge process with Monel 400 electrode. In order to design the experiments, the pulse on time and the pulse current were considered as input parameters. The SEM images indicated that the increase in the pulse on time and the pulse current can increase the thickness of the modified layer. Based on the obtained results, the thickness of improved layer varied between 35 to 75 microns. The results of the EDX analysis showed the diffusion of the copper and nickel to the aluminum surface. Moreover, the results of microhardness testing of the surface layer showed that after Electrical discharge process, the surface hardness has increased and the surface hardness as 35 Vickers has reached more than 400 Vickers.

Fabrication and characterization of alumina fiber by anodic oxidation and chemical dissolution processes

Alumina fiber was fabricated by an anodic oxidation process from pure aluminum or a chemical dissolution process from porous alumina. In the experiments, porous alumina layer was firstly formed on the surface of pure aluminum by anodic oxidation process in phosphoric acid electrolyte. The alumina fiber was obtained by either further anodic oxidation process or a chemical dissolution process from the porous alumina layer. The thickness of the porous alumina layer, the diameter and wall thickness of the pores in the porous alumina layer, and the length and diameter of the obtained alumina fiber were examined. The formation mechanism of the alumina fiber was discussed.

Influence of gold nanolayer coating on the continuous-wave laser ablation of a pure aluminum surface: Evaluations of structural and optical features

In this paper, formation of uniform and large-area micro/nanostructures on pure aluminum surfaces using a continuous-wave laser irradiation is presented. Gold nanolayer coating was utilized as a confinement layer for controlling the possible hydrodynamic phenomena in a molten area. Dependency of the laser-induced morphology on the thickness of a gold coating was investigated in this regard. Scanning electron microscopy, energy dispersive spectroscopy, grazing test of the X-ray diffraction, and optical absorption/reflection spectroscopy in UV/visible/IR ranges were employed to characterize the samples. Results showed that the formation of uniform structures of average sizes of 50 nm-5 μm on aluminum surface was possible following the irradiation of a continuous-wave CO2 laser, delivering 130 W beam power. Alterations of the surface morphology brought about an increase in specific absorption peaks at the UV region and the appearance of an absorption peak in the visible range. In addition, these structure-covered surfaces provided interesting reflection behaviors in different spectral areas, which can clearly reflect their high potential to be used as selective solar absorbers. The results of this investigation indicated that optical characteristics such as absorption and emission coefficients as well as ξ factor were 0.98, 0.13, and 7.53, respectively. It can therefore be concluded that this process can be considered an efficient and fast technique to fabricate selective solar absorbers.

A research of the stability of oxide-covered aluminum surface for electrochemiluminescence probe use

A research on the effect of different buffers on the pH range of 6–10 on the thin oxide-covered surface of aluminum cathode has been conducted under the conditions corresponding with those generally used in bioaffinity assays or other determinations made by using aluminum probe based on time-resolved cathodic electrochemiluminoimmuno assay (tr-ECLIA or tr-CECLIA) detection. The experiments have been conducted on impedance and cathodic electrochemiluminescence (CECL) basis using a strong long lifetime having electroluminophore Tb(III)-1 chelate where the ligand 1 is 2,6-bis[N,N-bis(carboxymethyl)aminomethyl]-4-benzoylphenol and Ruthenium(II) tris(2,2′–bipyridine) (Ru(bpy)32+) as the CECL model luminophores. The results point out that the natural oxide layer at the electrode surface does not essentially change as to its thickness but as to its resistance, it can be concluded that the best buffer in these luminophore determinations based on CECL and Al probe use is borate buffer adjusted to pH around 7–8 where the surface of aluminum has its neutral character. In the bioaffinity assays the meaning of the buffer seems to be more difficult to realize due to the complex character of the surface with plenty of different coatings and special handling steps but still with the aforementioned borate buffer the results were noticed to be the most stabile. The tests also pointed out that the character of the pure aluminum surface and the oxide layer above it without any other coatings could be strongly affected by the surrounding solution composition and in that way to the durability of the aluminum probe already during the quite short exposure times. The reported results are useful especially in the field of CECL based on aluminum probe use but could also in a certain extent to be utilized in a large scale of analysis considering the use of aluminum probes.

Effect of potassium permanganate on corrosion and wear properties of ceramic coatings manufactured on CP-aluminum by plasma electrolytic oxidation

Ceramic coatings were produced on the surface of commercially pure (CP) aluminum using plasma electrolytic oxidation in electrolyte solutions containing potassium permanganate. Morphology, microstructure, chemical composition and microhardness of the coatings were studied in different conditions. The effects of potassium permanganate concentration on the corrosion and wear behavior of the coatings were also investigated. The phase analysis indicated that the ceramic coatings composed of Al2O3, MnO, Mn3O4, and Mn2O3. Additions of potassium permanganate to the electrolyte lead to some new findings. The applied voltages and currents of the PEO process had lowered significantly. It had a beneficial in-situ sealing effect on the porous coatings. The corrosion and wear properties of the coatings were improved significantly by addition of potassium permanganate. Variation of the concentration of potassium permanganate changed the thickness and smoothness of the surfaces. Result indicated that formation of PEO coatings on pure aluminum has improved its corrosion resistance. Increasing the concentration of potassium permanganate resulted in high thickness and uniform microstructure coatings, caused the corrosion resistance of the samples to be increased. Creating a ceramic coating on the surface of pure aluminum increased its hardness and wear resistance and reduced the friction coefficient.

Influences of L-Cysteine/Zinc Oxide Additive on the Electrochemical Behavior of Pure Aluminum in Alkaline Solution

Severe self-corrosion is the main barrier preventing the application of aluminum as an anode material in alkaline air battery. In this work, a hybrid organic/inorganic inhibitor based on L-Cysteine/zinc oxide was tested to see if its addition to alkaline electrolyte can reduce self-corrosion of a commercial 1060 pure aluminum. Results obtained have shown that self-corrosion of pure aluminum is significantly restrained by the L-Cysteine/ZnO hybrid inhibitor without affecting its discharge performance. An interaction between ZnO and L-Cysteine leads to formation of a dense layer on pure aluminum surface. In both NaOH + ZnO and NaOH + L-Cysteine + ZnO solutions, the reaction mechanism is mainly controlled by diffusion of zincate ions. By using the L-Cysteine/ZnO hybrid inhibitor, cheap commercial 1060 pure aluminum can replace expensive 5N5 super-pure aluminum to achieve a comparable performance. This has been demonstrated in this study by comparing the battery based on commercial 1060 pure aluminum with the L-Cysteine/ZnO inhibitor and the battery made of 5N5 super-pure aluminum with 4 M NaOH solution.

Influence of surface pretreatments on the quality of trivalent chromium process coatings on aluminum alloy

The effects of surface pretreatments (degreasing and pickling) on the characteristics of the Trivalent Chromium Process (TCP) coating on pure aluminum and on AA2024-T351 aluminum alloy were investigated here by means of surface sensitive techniques: X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The XPS and ToF-SIMS results evidence that the TCP coating homogeneity is strongly dependent on the pretreatment process used. The TCP coverage factor, calculated from XPS results, is significantly lower, on both pure aluminum and AA2024-T351 alloy surface, when a pickling step is applied. One of the main effects of pickling pretreatment is strong metallic copper enrichment at the surface of the 2024 alloy, associated with chemical dissolution of Al-Cu intermetallic particles. However, it is evidenced here, that the copper enrichment is not detrimental for the quality of the TCP coating. The coating failure, observed when the pickling step is applied, can be assigned to a faster kinetics of the coating growth leading to formation of thicker conversion coating more susceptible to cracking or to the localized presence of aluminum fluoride species leading to the appearance of coating defects or detachment.

Friction stir clinching of alclad AA2024-T3 sheets

In order to improve corrosion resistance, alclad aluminum sheets, which are formed from pure aluminum surface layers cladded on high-strength aluminum alloy core sheets, are widely used in industry. However, in the conventional welding process, the alclad layer on the faying surface is a tough barrier, which significantly reduces weld strength. Therefore, friction stir clinching (FSC), a variant of friction stir spot welding (FSSW), was developed for joining alclad AA2024-T3 sheets. In this study, a FSC tool with a flat shoulder and a smooth probe, and a FSC die with a grooved circular cavity were used to make joints. The effects of important processing parameters on the mechanical performance of FSC joints were studied. A set of valid processing parameters was obtained. Untested and tested FSC joints were then examined using optical micrographs. The results indicated that the mechanical interlock and alclad layer shape of FSC joints are strongly correlated with their fracture and fatigue performance. Finally, a comparison with the mechanical performance of solid rivets and swept friction stir spot welds (swept-FSSWs) confirmed the feasibility of the FSC process for alclad aluminum sheets.

Low power CO2 laser modified iron/nickel alloyed pure aluminum surface: Evaluation of structural and mechanical properties

Surface modification of metals is demanding for high strength industrial purposes. Weak mechanical properties of aluminum (Al) are disadvantageous for several applications and needs improvement. We modify the surface of pure Al substrate by alloying it with a thick layer of Fe-Ni, where a low power (27 watt) cw CO2 laser with varying exposure time (30, 40 and 50s) is used. The exposure time dependent microstructure, surface morphology, and surface hardness of the achieved inter-metallic alloyed samples are determined. Microstructure analysis revealed the formation of different phases (Al0.9Ni1.1, AlNi3, Al6Fe, AlFe3, Al5Fe2 and Al76.8Fe14, Al5FeNi) with chemical heterogeneity. Alloyed sample displayed enhanced surface hardness (varied from 27HV0.1 to 53.9HV0.1) for extended laser radiation exposure time (from 30 to 50s). A new inter-metallic compound aluminum-iron-nickel (Al-Fe-Ni) with considerably tougher surface is achieved. Our observations may contribute towards the development of laser assisted modification of metal surface alloying.

Robust superhydrophobic surface on Al substrate with durability, corrosion resistance and ice-phobicity.

Practical application of superhydrophobic surfaces is limited by the fragility of nanoscale asperities. Combining chemical etching and anodization, microscale pits and nanoscale pores, instead of the micro and nano protrusions on traditional superhydrophobic surfaces mimicking Lutos leaves, were fabricated on commercially pure aluminum surfaces. After modified by FDTS, the surfaces were superhydrophobic and self-cleaning. The ultrahigh hardness and electrochemical stability of Al2O3 coating endowed the surface excellent mechanical durability and good corrosion resistance. Because the method is scalable, it may find practical application on body panels of automobiles and aircrafts and so on.

One-step fabrication of near superhydrophobic aluminum surface by nanosecond laser ablation

Inspired by the micro and nano structures of biological surface such as lotus leaf, rice leaves, etc. a functional near superhydrophobic surface of pure aluminum has been fabricated using one-step nanosecond laser processing. Thin aluminum sheets are micro-patterned with ultraviolet laser pulses to create near superhydrophobic surface in one-step direct laser writing technique. The impact of number of pulses/microhole with respect to the geometry and static contact angle measurements has been investigated. The microstructure shows the formation of blind microholes along with the micro-wall by laser processing, which improves the composite interface between the three phases such as water, air and solid, thus enhance the wetting property of the surface. The geometrical changes are supported by the chemical changes induced on the surface for improving the degree of hydrophobicity. Laser processed microholes exhibited near superhydrophobic surface with SCA measurement of 148±3°. The static contact angle values are very consistent for repeated measurement at same area and across the laser patterned surface.