Untreated Aluminum Research Articles

Corrosion Behaviour of Heat Treated 1060 Aluminium in Dilute Acid Solutions

The electrochemical corrosion behaviour of untreated, quenched and annealed cold rolled 1060 aluminium specimens was studied through weight loss measurement, potentiodynamic polarization technique and optical microscopy in 0.5, 1, 1.5 and 2M H2SO4 and HCl solutions. Data obtained from the tests show that the quenched specimens had the highest corrosion resistance as a result of its hardened surface due to retained saturated solid solution. The untreated aluminium specimens exhibited a lower corrosion resistance than the quenched specimens though the corrosion rates from HCl solution are generally higher than values obtained from H2SO4. Annealed specimens had the highest corrosion rate as its passive protective film resulting from the rearrangement of its microstructural constituents could not sustain the aggressive attack of corrosive anions within the acid solution. Micrographs from optical microscopy showed a severely deteriorated annealed morphology resulting from depletion of the grain boundary. Corrosion pits were observed in the untreated specimens while the quenched specimens showed limited deterioration due to general corrosion

On the Improvement of AA2024 Wear Properties through the Deposition of a Cold-Sprayed Titanium Coating

This paper deals with the study of the enhancement of the tribological properties of AA2024 through the deposition of a titanium coating. In particular two different coatings were studied: (1) untreated titanium coating; and (2) post-deposition laser-treated titanium coating. Titanium grade 2 powders were deposited onto an aluminium alloy AA2024-T3 sheet through the cold gas dynamic spray process. The selective laser post treatment was carried out by using a 220 W diode laser to further enhance the wear properties of the coating. Tribo-tests were executed to analyse the tribological behaviour of materials in contact with an alternative moving counterpart under a controlled normal load. Four different samples were tested to assess the effectiveness of the treatments: untreated aluminium sheets, titanium grade 2 sheets, as-sprayed titanium powders and the laser-treated coating layer. The results obtained proved the effectiveness of the coating in improving the tribological behaviour of the AA2024. In particular the laser-treated coating showed the best results in terms of both the friction coefficient and mass lost. The laser treatment promotes a change of the wear mechanism, switching from a severe adhesive wear, resulting in galling, to an abrasive wear mechanism.

Wear Behavior and Mechanism of a Sliding Pair of 0. lC-3Cr-2W-V Nitrided Steel Rubbing against an Aluminum Bronze Alloy

AbstractWear behavior and mechanism of plasma nitrided steel oscillating against a heat-treated and an untreated aluminum bronze alloy were investigated using an Optimol SRV tribometer. The influence of heat treatment on the mechanical properties of the alloy was evaluated. Furthermore, the wear debris was also examined to understand the wear mechanisms. The results show that a 220–230 μm nitrided layer, which was harder than the substrate, was obtained on the steel surface. The tensile strength and hardness of the alloy are found to be significantly improved by the heat treatment associated with low impact toughness. The heat treatment of the alloy did not obviously decrease the friction coefficient of the nitrided steel-bronze couple. However, the wear loss of the nitrided steel increased when it mated with the treated bronze by a severe three-body abrasion. The nitrided steel was mainly damaged by fatigue spalling. Under plane contact conditions, the wear debris was mainly generated from the bronze part and can escape from the interface before being oxidized, leading to the phase structure of all the debris being copper rather than copper oxides.

Densification of frost on hydrophilic and hydrophobic substrates – Examining the effect of surface wettability

The properties of a growing frost layer were analyzed and compared for surfaces of different wettability to determine the effect that the surface energy has on the frost mass, thickness, and density. Three surfaces were tested – an uncoated, untreated aluminum plate (Surface 1), an identical plate coated with a hydrophobic coating (Surface 2), and a plate containing a hydrophilic coating (Surface 3). For these experiments, the frost layer was grown for a three-hour period inside a Plexiglas environmental test chamber where the relative humidity was held constant (i.e. 60%, 80%) using an ultrasonic humidifier. The surface temperature of the plate was fixed using a thermoelectric cooler (TEC) and monitored by four thermocouples affixed to the surface and stage. Frost thickness was determined from images of the frost layer taken using a CCD camera mounted directly overhead. A reduction in frost density of 37–41% was observed on the hydrophobic surface (Surface 2), whereas an increase of 20–26% was consistently observed on the hydrophilic surface (Surface 3) as compared to the baseline surface. Frost layer property data were also compared against models found in the literature. Reasonably good agreement was observed when comparing against data from the baseline surface; however, the agreement was not generally as good when compared against the hydrophilic and hydrophobic surfaces suggesting the need for surface wettability to be included as a parameter in future frost densification models.

The influence of different pre-treatments of current collectors and variation of the binders on the performance of Li4Ti5O12 anodes for lithium ion batteries

In order to optimize the electron transfer between the Li4Ti5O12-based active mass and the current collector, the surface of aluminum foil was modified either by alkaline etching or by a carbon coating. The as-modified aluminum foils were coated with an active mass of Li4Ti5O12 mixed with polyvinylidene fluoride, sodium carboxymethyl cellulose, or polyacrylic acid as binders. Untreated aluminum and copper foils served as reference current collectors. The corrosion reactions of aluminum foil with the applied binder solutions were studied and the electrode structure has been analyzed, depending on the binder. Finally, the electrochemical performance of the prepared electrodes was investigated. Based on these measurements, conclusions concerning the electrical contact between the different current collectors and the active masses were drawn. The energy density of the Li4Ti5O12 electrodes cast on carbon-coated aluminum foils was significantly increased, compared to the corresponding electrodes with a copper current collector.

Liquid phase surface nitriding of aluminium using TIG process

Liquid phase surface nitriding of AA5052 aluminium was performed using the heat of a TIG (tungsten inert gas) torch in a gas shielding which was a mixture of argon and nitrogen. The feasibility of obtaining nitride compounds at various TIG processing parameters and nitrogen contents in the shielding gas were studied. The presence of AlN phase was proved by X-ray diffraction analysis. Scanning electron microscopy with EDS analyser was carried out to study the morphology and chemical composition of the nitride phase. The microhardness test was also performed on cross sections of treated layers. This measurement demonstrated that the surface hardness of the untreated aluminium was increased from 52 HV for the untreated aluminium alloy to as high as 1411 HV for the nitrided sample. It was also noticed that liquid phase surface nitriding reduced the wear rate to less than quarter of that of the untreated substrate.

Experimental analysis of steam condensation over conventional and superhydrophilic vertical surfaces

Nano-engineered surfaces have been recently studied as a promising solution for many heat transfer applications. In particular, it is known that superhydrophobic surfaces, obtained by combining low surface free energy with micro-/nano-scale surface roughness, can promote dropwise condensation mode, while superhydrophilic ones, obtained for example by roughening the substrate to a micro-/nano-scale morphology, showed promotion of film formation during condensation. In the open literature there is a lot of information regarding the fabrication and characterization of these surfaces, but very few results on the heat transfer performance are reported.In this paper, a new experimental apparatus for investigation of condensation of pure steam, flowing at different velocities, is presented. Filmwise condensation is investigated over untreated aluminum surfaces placed inside a rectangular narrow channel. The effect of wall subcooling and vapor velocity on the two-phase heat transfer coefficient is experimentally and theoretically analyzed. Condensation tests are also performed over a superhydrophilic surface, aiming at analyzing the effects of the wetting properties of the substrate on the process. A comparison between the heat transfer coefficients measured on the superhydrophilic surface and the ones obtained on the untreated sample shows a penalizing effect of the hydrophilic treatment.

Facile and fast fabrication method for mechanically robust superhydrophobic surface on aluminum foil

This work reports a simple method to fabricate superhydrophobic surfaces on aluminum foil via high-field electrochemical anodization in oxalic acid aqueous solution. Different morphologies of these superhydrophobic surfaces can be obtained by adjusting anodization time and current. These surfaces reveal remarkable superhydrophobicity after the modification of fluorinated silane solution. The maximum contact angle (CA), 163°±2°, can be easily obtained by this simple method. And the sliding angle (SA) is less than 2°. The superhydrophobic surface shows a long-term stability over a wide pH range. The corrosion current density of the superhydrophobic aluminum is reduced by about one order of magnitude compared to the untreated aluminum. This fabricated superhydrophobic surface has a promising application in anti-corrosion fields.

Experimental study of dew formation on metal radiant panels

The risk of condensation on radiant cooling panels used in hot and humid regions has limited their application and broad adoption in the market. This paper describes an experimental study of dew formation on metal radiant panels. Two metal radiant panels with hydrophobic and untreated aluminum alloy surfaces were prepared for investigation and a constant temperature and humidity environmental chamber was employed to simulate the various indoor thermal environments. The results indicate that sub-cooled degrees had a significant effect on the elapsed time from the condensate nucleating to falling off the horizontal radiant panels, which was over 10h at a sub-cooled degree less than 3°C. In addition, the hydrophobic surface demonstrated a delaying effect on the dew formation on the radiant panels. The feature size of the critical pendant droplet falling off the hydrophobic surface (with a contact angle of 96.7°) was 5.6mm, while that of the untreated aluminum alloy surface (with a contact angle of 66.1°) was 7.3mm. Furthermore, simulation results show that the feather size of the critical pendant droplet falling off the horizontal surface decreases as the contact angle increases. Based on these results, hydrophobic surfaces represent a promising new method for limiting condensation on radiant panels.

Fluorine plasma treatment of bare and nitrilotris(methylene)triphosphonic acid (NP) protected aluminum: an XPS and ToF-SIMS study

Nitrilotris(methylene)triphosphonic acid (NP) is a technologically important molecule that has been used for years as a corrosion inhibitor and/or adhesion promoter on aluminum and other metal surfaces. However, to the best of our knowledge, the detailed surface characterization of NP adsorbed on aluminum, or on any other surface, has not been reported. Herein, we report an X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis of a series of untreated and NP-coated aluminum substrates that were exposed to the downstream products of a fluoroalkane + oxygen plasma for different amounts of time (from 0 to 20 s). As indicated by P 2p, N 1s, Al 2p, O 1s, and F 1s narrow scans, even a 4-s plasma treatment significantly damages the NP protective layer and converts the native aluminum oxide into aluminum oxyfluoride. Heat treatment of the fluorine plasma-treated samples in the air substantially converts the aluminum oxyfluoride back to aluminum oxide, while similar heating under vacuum results in little change to the materials. A slow loss of fluorine from the samples occurs over the course of weeks when they are stored in the air. A ToF-SIMS analysis reveals sets of signals that are consistent with no surface treatment, NP treatment, or fluorine plasma treatment. A principal component analysis of the negative ion ToF-SIMS spectra from the samples shows the expected differentiation of the samples. Copyright © 2014 John Wiley & Sons, Ltd.

Impact dynamics of high Weber number drops on chemically modified metallic surfaces

Hydrophobic/superhydrophobic metallic surfaces prepared via chemical treatment are encountered in many industrial scenarios involving the impingement of spray droplets. The effectiveness of such surfaces is understood through the analysis of droplet impact experiments. In the present study, three target surfaces with aluminum (Al-6061) as base material–acid-etched, Octadecyl Trichloro Silane (OTS) coated, and acid-etched plus OTS-coated–were prepared. Experiments on the impact of inertia dominated water drops on these chemically modified aluminum surfaces were carried out with the objective to highlight the effect of chemical treatment on the target surfaces on key sub-processes occurring in drop impact phenomenon. High speed videos of the entire drop impact dynamics were captured at three Weber number (We) conditions representative of high We (We>200) regime. During the early stages of drop spreading, the drop impact resulted in ejection of secondary droplets from spreading drop front on the etched surfaces resembling prompt splash on rough surfaces whereas no such splashing was observable on untreated aluminum surface. Prominent development of undulations (fingers) were observed at the rim of drop spreading on the etched surfaces; between the etched surfaces the OTS-coated surface showed a subdued development of fingers than the uncoated surface. The impacted drops showed intense receding on OTS-coated surfaces whereas on the etched surface a highly irregular receding, with drop liquid sticking to the surface, was observed. Quantitative analyses were performed to reveal the effect of target surface characteristics on drop impact parameters such as temporal variation of spread factor of drop lamella, temporal variation of average finger length during spreading phase, maximum drop spreading, time taken to attain maximum spreading, sensitivity of maximum spreading to We, number of fingers at maximum spreading, and average receding velocity of drop lamella. Existing models for maximum drop spreading showed reasonably good agreement with the experimental measurements on the target surfaces except the acid-etched surface.

Combustion Characteristics of Composite Solid Propellants Containing Different Coated Aluminum Nanopowders

Aluminum nanopowders coated with oleic acid (nmAl+OA), perfluorotetradecanoic acid (nmAl+PA) and nickel acetylacetonate (nmAl+NA) were prepared. The combustion characteristics of hydroxyl terminated polybutadiene (HTPB) composite solid propellants containing different coated aluminum nanpowders were investigated. The result shows that the burning rate of the propellant sample containing nmAl+NA is the highest at different pressure, the maximum burning rate is up to 26.13 mm·s-1at 15 MPa. The burning rates of propellant samples containing nmAl+OA and nmAl+PA are almost the same at different pressures, and higher than the propellant samples containing untreated aluminum nanopowders only at the pressure range of 10 ~ 15 MPa. The flame brightness of different propellants under different pressure is not the same. The flame brightness is increased with the pressure increasing. The flame center zone brightness of the propellant containing nmAl+PA and nmAl+NA is brighter under 4 MPa, and the brightness of nmAl+NA is the brightest. The surface coating of aluminum nanopowder has little effect on the combustion flame temperature of solid propellant. The burning surface temperature increases with the pressure increasing.

The Preparation and Performance of LC4 Aluminum Alloys Ceramic Coatings with Trace Loose Layer Treated by Micro-Arc Oxidation

LC4 aluminum alloy samples were treated by micro-arc oxidation (MAO) to produce trace loose layer film to improve the surface properties. The mechanical characteristics, high temperature erosion performance, structure and composition were investigated by strength tester, high flame erosion, scanning electron microscopy and energy-dispersive X-ray spectrometry. Compared to the untreated aluminum alloy, MAO coatings have good mechanical performance with tensile strength bigger than 18MPa and is intact with 20s heat ablation of 1900°C.

The ice repellency of plasma polymerized hexamethyldisiloxane coating

A superhydrophobic thin film was deposited on an aluminium oxide substrate by low pressure plasma polymerization of hexamethyldisiloxane (HMDSO). The coating was determined to be superhydrophobic due to its high water contact angle (∼158°) and low contact angle hysteresis. The aim of this work is to verify the icephobic properties of the HMDSO thin films obtained under simulated atmospheric conditions in a wind tunnel at sub-zero temperature and subsequent centrifugal adhesion test. The results obtained showed that the ice adhesion strength of the superhydrophobic HMDSO coating was 3.5 times lower than that on an aluminium substrate as reference tests. Although ice adhesion strength of the surface increased after 15 times icing/de-icing cycles, the surface kept its icephobic properties (ice adhesion strength 1.4 times lower than untreated aluminium).

Influence of microstructured substrate on solar selective absorbing films

In this paper, the influence of the substrate on the performance of solar selective absorbing films is considered experimentally. The microporous structures of aluminium foils are fabricated by a two-step anodisation method and TiNxOy multilayer films are deposited on untreated aluminium foils, polished aluminium foils and porous aluminium foils respectively. It is found that the solar selective absorbing performance of multilayer films is dependent on the microstructure of substrate surfaces. The films on the substrate after polishing treatment have the lowest absorptance. The surface oxide layer, which is a porous structured layer on aluminium foil, can result in the increase of the absorptance α and the emittance ϵ of the solar films. The reflectance of the film deposited on the microstructured substrate is lower in general. Moreover, the thickness of the surface oxide layer can be moderated to decrease thermal emittance of the solar selective absorbing films.

Cavitation erosion resistance of microarc oxidation coating on aluminium alloy

Two ceramic coatings are prepared on 2124 aluminum alloy by microarc oxidation (MAO) technology. To explore the cavitation erosion resistance of the MAO coating, cavitation tests were performed by using a rotating-disk test rig. The mass losses, surface morphologies, chemical compositions and the phase constituents of the samples after cavitation tests were examined by using digital balance, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), respectively. The results indicate that the MAO coatings can extend the incubation period of aluminum alloy, and thus enhance the cavitation erosion resistance as compared to the untreated aluminum alloy samples. After duration of 63h cavitation test, a lot of erosion pits and the particles in various shapes can be observed on the surfaces of the aluminum alloy samples, while only a few erosion pits are observed on the MAO coatings. Moreover, the mean depths of erosion on the MAO coatings are lower in the first 30h and are independent on erosion time. The results show that the cavitation erosion of MAO coating is governed by water mechanical impaction, resulting from the effects of brittle fracture of the MAO coating.

Experimental investigation of pool boiling heat transfer and critical heat flux of nanostructured surfaces

The present study aims to investigate the effect of pool boiling on nanostructured surfaces. For this purpose, nanocoating was performed on aluminum surface specimens by anodizing and their boiling heat transfer characteristics were compared with those of bare surface of aluminum. Also, the critical heat flux and boiling heat transfer coefficients were evaluated experimentally. Chromic acid and sulfuric acid solutions were utilized as the electrolytes. Prior to anodizing, sandblasting and etching were applied as mechanical and chemical treatments of the surfaces. The coating was performed over three different durations. The maximum critical heat flux was observed to occur in samples which had been weakly etched and anodized for 30min in the sulfuric acid solution. Critical heat flux increased by 8% compared with that of the untreated aluminum alloy surface. Also, boiling heat transfer coefficient increased by 159% in weakly etched samples. In order to investigate surface characteristics, contact angle and atomic force microscope (AFM) images were used. The surface roughness and real area were measured in six samples. The AFM images indicated that surface roughness increased with anodizing time. The change in roughness was more pronounced in surfaces treated in the chromic acid solution compared with those treated in the sulfuric acid solution.

Inhibition of ice nucleation by slippery liquid-infused porous surfaces (SLIPS)

Ice repellent coatings have been studied and keenly sought after for many years, where any advances in the durability of such coatings will result in huge energy savings across many fields. Progress in creating anti-ice and anti-frost surfaces has been particularly rapid since the discovery and development of slippery, liquid infused porous surfaces (SLIPS). Here we use SLIPS-coated differential scanning calorimeter (DSC) pans to investigate the effects of the surface modification on the nucleation of supercooled water. This investigation is inherently different from previous studies which looked at the adhesion of ice to SLIPS surfaces, or the formation of ice under high humidity conditions. Given the stochastic nature of nucleation of ice from supercooled water, multiple runs on the same sample are needed to determine if a given surface coating has a real and statistically significant effect on the nucleation temperature. We have cycled supercooling to freezing and then thawing of deionized water in hydrophilic (untreated aluminum), hydrophobic, superhydrophobic, and SLIPS-treated DSC pans multiple times to determine the effects of surface treatment on the nucleation and subsequent growth of ice. We find that SLIPS coatings lower the nucleation temperature of supercooled water in contact with statistical significance and show no deterioration or change in the coating performance even after 150 freeze-thaw cycles.

Synthesis and properties of PANI/SiO2 organic–inorganic hybrid films

PANI/SiO2 organic–inorganic hybrid films were prepared directly from polyaniline (PANI) emulsion solution and tetraethyl orthosilicate (TEOS) by sol–gel process. The evolution of phase, morphology and corrosion resistance ability of PANI/SiO2 hybrid materials were characterized by TG, FTIR, SEM and potentiodynamic polarization analysis. It was demonstrated that PANI/SiO2 organic–inorganic hybrid films have a homogeneous and smooth surface without detectable cracks. Potentiodynamic polarization analysis revealed that the hybrid films provided an exceptional barrier and corrosion protection in comparison with untreated aluminum alloy substrates. However, the increase of TEOS content in PANI/SiO2 organic–inorganic hybrid materials tends to exhibit brittleness and micro-cracks which will lead to the deterioration of corrosion resistance ability.

Improving the shear strength by silane treatments of aluminum for direct joining of phenolic resin

Phenolic resin was directly joined to aluminum using three different silane coupling agents, AEAPS (N-(β-aminoethyl)-γ-aminopropyl trimethoxy silane), McPS (γ-mercaptopropyl trimethoxy silane), and GPS (γ-glycidoxypropyl trimethoxy silane). The impacts of surface treatment conditions on the joint strength and interfacial properties were investigated. The joint strength was raised about 1.6–2.6 times that of the untreated aluminum when joined to phenolic resin. The chemical bonds were formed by the phenolic resin and the amino groups in AEAPS, while entanglement between the phenolic resin and the methylene groups in McPS was obtained. The results of cyclic thermal loading indicated that the interfaces were deteriorated and joint strength was decreased using GPS as the silane coupling agent when the number of cycles was increased. The interface was enhanced and the shear strength of joints was not decreased using AEAPS as the silane coupling agent.