As-received Aluminum Research Articles

Superhydrophobic surfaces with a dual-layer micro- and nanoparticle coating for drag reduction

We propose a facile and cost effective method for fabricating superhydrophobic surfaces with significant drag reduction in a wide velocity range. A dual structure superhydrophobic aluminum surface with a hydrophobic Al2O3 micro- and nanoparticle coating and also another superhydrophobic surface with a nanoparticle layer coating are fabricated. Then, the resulted drag from each of these surfaces is measured carefully in different velocities and compared with the drag of the as-received aluminum surface. Our results reveal that the surface with the dual structure experiences drag reduction in a wider velocity range compared with the nanoparticle coated sample. Drag reduction of the dual structure substrate is between 77 and 5% for Reynolds number of 4.7 × 104 and 2.35 × 105, respectively. The fabricated dual structure also shows a good durability which makes it favorable for many applications.

Powder processing methodology for production of graphene oxide reinforced aluminium matrix composites

In this paper, the preparation and properties of reduced graphene oxide (rGO) reinforcement of aluminium matrix nanocomposites (AMCs) are presented. The commercial colloidal graphene oxide was firstly coated on the selected aluminium powder particles, and the graphene oxide was then reduced through thermal annealing process. The rGO-aluminium powder dispersions were prepared in order to provide coated aluminium particles before synthesis of the metal matrix nanocomposites. As-received pristine aluminium powder and pre-synthesised rGO-AMCs were cold compacted into disc-shaped specimens and sintered. The mechanical properties and microstructure were studied and characterised via Vickers hardness, a flexural bending test, X-ray diffraction and scanning electron microscopy. The rGO was observed to be dispersed effectively in the aluminium matrix and well consolidated within the composites. The relevant factors for the powder metallurgy process, e.g. compaction pressure, density, sintering conditions, have been elaborated and optimised. Enhancements of 32% in micro hardness of 0.3 wt.% rGO-Al composites were observed compared to the baseline pure aluminium prepared under identical experimental conditions. The graphene oxide and graphene nanosheets have proven potentially capable of realising mechanical reinforcements in aluminium matrix composites under cold compaction and sintering powder metallurgy techniques only.

Joining Mechanism of Dissimilar Materials such as Metal and Plastic Sheets by Friction Lap Joining

It is difficult to join dissimilar materials such as metallic material and polymer. We have investigated to join Aluminum alloy and high density polyethylene (PE) and ethylene acrylic acid copolymer (EAA) using Friction Lap Joining (FLJ) and then concluded EAA could be strongly joined with Aluminum alloy. PE could not be joined without anodizing. We have considered that EAA has a polar functional group, COOH. On the contrary, PE cannot be joined to an as-received aluminum alloy, because PE has no polar functional group. So, we have tried to confirm this mechanism with XPS and FTIR to investigate the interface between anodized surface and that of polymer. We find that the possibility of chemical bonding arises between O-H in COOH and O in Al2O3or O in C=O and O in Al2O3 at elevated temperature.

Durability and characterization studies of chromium carbide coated aluminum fuel cell stack

Corrosion and interfacial contact resistance measurements were performed on chromium carbide coated aluminum 6061 and as-received aluminum 6061 samples. The coating was thermally sprayed onto the aluminum sample using the High Velocity Oxygen Fuel (HVOF) thermal spray technique. The chromium carbide coating consists of Cr3C2 top layer and CrCNi intermediate layer. The coating thickness was approximately 150 μm. A three-cell stack with chromium carbide coated aluminum bipolar plates was also fabricated for the durability and characterization studies. The coating thicknesses on the lands of the ribs and the walls of the valleys were approximately 300 μm and 150 μm, respectively. The stack was operated at the temperatures of 37 °C for 250 h and 80 °C for additional 500 h. The scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX) analysis shows that the thickness, chemistry, and surface morphology of the coating material remained consistent after 750 h of operation. The inductively coupled plasma – optical emission spectroscopy (ICP-OES) analysis was performed on the samples of membrane electrode assembly (MEA) and byproduct water that was produced during the fuel cell electrochemical reaction.

Fabrication of Corrosion Resistance Micro-Nanostructured Superhydrophobic Anodized Aluminum in a One-Step Electrodeposition Process

The formation of low surface energy hybrid organic-inorganic micro-nanostructured zinc stearate electrodeposit transformed the anodic aluminum oxide (AAO) surface to superhydrophobic, having a water contact angle of 160°. The corrosion current densities of the anodized and aluminum alloy surfaces are found to be 200 and 400 nA/cm2, respectively. In comparison, superhydrophobic anodic aluminum oxide (SHAAO) shows a much lower value of 88 nA/cm2. Similarly, the charge transfer resistance, Rct, measured by electrochemical impedance spectroscopy shows that the SHAAO substrate was found to be 200-times larger than the as-received aluminum alloy substrate. These results proved that the superhydrophobic surfaces created on the anodized surface significantly improved the corrosion resistance property of the aluminum alloy.

Processing–structure–property correlation in nano-SiC-reinforced friction stir welded aluminum joints

In this work, friction stir welding (FSW) of AA5086-H34 aluminum with nano-sized SiC reinforcement is performed. The effects of traverse and rotational speeds and number of passes on microstructure, hardness, and tensile behavior of the FSWed joints are studied. Single-pass FSWed specimens containing reinforcements represented SiC particle-rich and SiC particle-free regions in grain refined Al-matrix within the stir zone (SZ), which could be affected by changing traverse and rotational speeds. Multi-pass FSW led to more grain refinement and homogenous distribution of SiC particles. Hardness measurement revealed that both single- and multi-pass FSW with SiC particles increased hardness values. Furthermore, tensile tests demonstrated that single-pass FSWed specimens with SiC possessed lower tensile strength and percentage of elongation in comparison to as-received aluminum and showed brittle fracture in the stir zone, while a remarkable increase in tensile properties was observed for multi-pass FSWed specimens with SiC particles and consequent ductile fracture in base metal.

Three-dimensional characterization of fatigue-relevant intermetallic particles in high-strength aluminium alloys using synchrotron X-ray nanotomography

Second-phase particles and small porosities are known to favour fatigue crack initiation in high-strength aluminium alloys 2050-T8 and 7050-T7451. Using high-resolution X-ray tomography (320 nm voxel size), with Paganin reconstruction algorithms, the probability that large clusters of particles contain porosities could be measured for the first time in 3D, as well as precise 3D size distributions. Additional holotomography imaging provided improved spatial resolution (50 nm voxel size), allowing to estimate the probability of finding cracked particles in the as-received material state. The extremely precise 3D shape (including cracks) as well as local chemistry of the particles has been determined. This experiment enabled unprecedented 3D identification of detrimental stress risers relevant for fatigue in as-received aluminium alloys.

Superhydrophobic aluminum alloy surfaces prepared by chemical etching process and their corrosion resistance properties

Superhydrophobic aluminum alloy surfaces are obtained by chemical etching using 1M NaOH solution followed by passivation using 0.01M ethanolic stearic acid (SA) solution. The formation of low surface energy aluminum stearate takes place during the passivation process between stearic acid and hydroxyl group-terminated aluminum alloy surfaces. A schematic model of the SA passivation process on the OH terminated Al-surfaces is presented in this work. The flake-like micro-nanostructure morphology of the low surface energy aluminum stearate increases the water contact angle by more than 150°, demonstrating the superhydrophobic properties. The corrosion current density reduces and polarization resistance increases systematically with increasing passivation time. The polarization resistance, calculated from the Tafel curve of the superhydrophobic surfaces prepared by stearic acid passivation for 60min, is determined to be 137 times larger than that of the as-received aluminum alloy substrate. Similarly, the modulus of impedance, as-determined from electrochemical impedance spectroscopy (EIS), is found to be 70 times larger for the superhydrophobic surfaces compared with the as-received aluminum alloy surface. These results demonstrate that the superhydrophobic aluminum alloy surfaces created by chemical etching followed by passivation have superior corrosion resistance properties than the as-receive aluminum alloy substrate.

Forming micro channels on aluminum foils by using flexible die forming process

A flexible die forming process is proposed to form aluminum micro channels with channel widths not larger than 1mm. Three micro channel dies and two different polyurethanes (40A and 90A) were used to form micro channels on the annealed and as-received aluminum foils (50 and 75μm). For understanding the influences of size effects, polyurethane hardness and channel width on forming micro channels, a series of experiments were conducted. Through using different annealing conditions, different grain sizes were obtained such that different T/D, the ratio of thickness and average grain size, could be obtained. T/D ratio is used as a parameter to model the size effects in the two models proposed in this paper. These two models can predict the depths of the micro channels formed by the proposed process, so they can be used by industry as a design tool for product design, process design and development, annealing process, etc.

In-Situ TiB2–TiC–Al2O3 Composite Coating on Aluminum by Laser Surface Modification

To improve the surface hardness of aluminum, in-situ TiB2–TiC–Al2O3 composite coating was deposited on it by pre-placed laser coating process using precursor mixture of (TiO2 + B4C) and (TiO2 + B4C + Al). Pulsed Nd:YAG laser was used to produce coating track by scanning a laser beam in overlapped condition. Multiple tracks again overlapped to get a wider coating area. Phase constituents and microstructure of the deposited coating were studied by XRD and FESEM analysis. Vickers micro-hardness tester was used to measure micro-hardness of the coating. Results indicate that, in appropriate laser processing condition, coating was obtained with metallurgical bonding to aluminum substrate. XRD and microstructure analysis confirms the formation of TiB2, TiC, and Al2O3 in the coating layer through in-situ reaction of reactant powders. Micro-hardness of the coating was found appreciably higher in comparison to the as-received aluminum substrate, due to presence of hard ceramic particles produced during in-situ reaction and their grain refinement for rapid cooling.

Effects of Hard Surface Grinding and Activation on Electroless-Nickel Plating on Cast Aluminium Alloy Substrates

This work examined effects of hard surface polishing grits and activation on electroless-nickel (EN) plating on cast aluminium alloy substrates in sodium hypophosphite baths. As-received aluminium alloy sample sourced from automobile hydraulic brake master cylinder piston was melted in electric furnace and sand cast into rod. The cast samples were polished using different grits (60 μm–1200 μm) before plating. The effects on adhesion, appearance, and quantity of EN deposits on substrates were studied. Observation shows that the quantity of EN deposit is partly dependent on the alloy type and roughness of the surface of the substrates, whereas the adhesion and brightness are not solely controlled by the degree of surface polishing. The best yield in terms of adhesion and appearance was obtained from the activation in zincate and palladium chloride solutions. Higher plating rates (g/mm2/min) of 3.01E-05, 2.41E-05, and 2.90E-05 were obtained from chromate, zincate, and chloride than 8.49E-06, 8.86E-06, and 1.69E-05 as obtained from HCl etched, NaOH, and H2O activated surfaces, respectively.

Effect of aluminum pre-straining on strength of clinched galvanized SAE1004 steel-to-AA6111-T4 aluminum

Normally, the sheet metal may be pressed or stamped prior to mechanical clinching. The pre-strain from the pressing or stamping may have an influence on the quality of the clinched joints. To understand how the pre-strained sheets materials affect the joint quality, we conducted the study to understand the effect of pre-straining aluminum on the static strength of the clinched aluminum-to-steel joint. The section parameters (i.e. undercut, neck thickness, and bottom thickness) and joint strength were measured. It was found that the work hardening resulting from pre-straining decreased the ductility of aluminum AA6111-T4 and induced some ductile damage on the clinched aluminum workpieces. A 5% pre-strain on AA6111-T4 caused a significant decrease (about 20%) in joint strength. Though the bottom thickness is a good indicator for detecting the strength variation for the clinched as-received and pre-strained aluminum–steel joints, it barely detected the effect of ductile damage in the pre-strained aluminum on the joint strength. The application of the similar “X” parameter (i.e., bottom thickness of the clinched joint) from the as-received aluminum to monitor the quality of the clinched steel-pre-strained aluminum joint resulted in overestimates of the joint strength. Therefore, the optimum clinching tools and process variables for clinching of the pre-strained AA6111-T4-to-steel cannot be derived from the experiments using the as-received aluminum workpieces. To obtain the desired strength of the joints made with dissimilar materials, it is important to achieve a good balance between the undercut and neck thickness by optimizing the clinching tools and process parameters. The variation of electrical resistance of the joints during the clinching process can differentiate the difference of the damage between the as-received and pre-strained clinched joints. Therefore, a method of monitoring the variation of electrical resistance is proposed to inspect the quality of the clinched steel-to-pre-strained aluminum joints.

SECM investigation of corrosion inhibition by tungstate- and vanadate-doped polypyrrole/aluminum flake composite coatings on AA2024-T3

Scanning electrochemical microscopy (SECM) experiments were performed over defects on AA2024-T3 samples coated with an epoxy-based composite containing aluminum flakes covered with either tungstate- or vanadate-doped polypyrrole. The SECM probe was scanned laterally over the defect with the probe potential set to either reduce dissolved oxygen (redox competition mode) or oxidize ferrocenemethanol (feedback mode). Scans were performed over several days of immersion in naturally aerated KCl/ferrocenemethanol solution and results from three different composite coatings were obtained. Coatings containing the as-received aluminum flakes with no polypyrrole showed high levels of corrosion and corrosion product buildup, while those coatings containing polypyrrole-covered flakes showed depletion of dissolved O2 over the scribe, but with no concomitant buildup of corrosion product. The results support a corrosion control mechanism that combines galvanic coupling between the polypyrrole and the aluminum flakes, anodic passivation of the substrate, and inhibitor release into the defect. SEM/EDX was utilized to provide evidence of corrosion product formation and the release of dopant ions.

Electrochemical synthesis of highly ordered polypyrrole on copper modified aluminium substrates

Fabrication of highly ordered conducting polymers on metal surfaces has received a significant interest owing to their potential applications in organic electronic devices. In this context, we have developed a simple method for the synthesis of highly ordered polypyrrole (PPy) on copper modified aluminium surfaces via electrochemical polymerization process. A series of characteristic peaks of PPy evidenced on the infrared spectra of these surfaces confirm the formation of PPy. The X-ray diffraction (XRD) pattern of PPy deposited on copper modified aluminium surfaces also confirmed the deposition of PPy as a sharp and intense peak at 2θ angle of 23° attributable to PPy is observed while this peak is absent on PPy deposited on as-received aluminium surfaces. An atomic model of the interface of PPy/Cu has been presented based on the inter-atomic distance of copper–copper of (1 0 0) plane and the inter-monomer distance of PPy, to describe the ordering of PPy on Cu modified Al surfaces.

Wear behavior of nanostructured Al/Al2O3 composite fabricated via accumulative roll bonding (ARB) process

In the present work, wear behavior of nanostructured aluminum and composite performed by accumulative roll bonding (ARB) process was investigated. The wear characteristics were studied by scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). Also, transmission electron microscopy (TEM) and crystallographic texture investigations were performed. The results indicated that the ARB process led to the decrease in wear resistance of the monolithic and composite samples compared with as-received aluminum strip. The adhesive, abrasive and delaminating wear mechanisms occurred in the monolithic and composite samples simultaneously. At higher number of ARB cycles, delamination was the dominant wear mechanism. It was found that the surface damage of the composite was more extensive than that of the monolithic sample due to the occurrence of spalling mechanism. It was suggested that the intense Rotated Cube {001}〈110〉 texture component of composite helped to crack nucleation and propagation greatly. The role of delamination and especially, spalling in decreasing the wear resistance of composite was very important such that it eliminated the role of reinforcing particles and grain size on the wear resistance.

Formation and Characterization of Ceramic Nanocomposite Crystalline Coatings on Aluminium by Anodization

Ceramic nanocomposite coatings have been synthesized on aluminium by using lithium sulphate electrolyte with zirconium silicate additive by anodization. The effects of current density (CD) on microhardness, structure, composition and surface topography of the oxide layer formed at various CDs (0.1–0.25 A/cm2) have been studied. Crystalline coatings formed at 0.25 A/cm2 have been (width 95 nm) observed with a relatively uniform distribution confirmed by scanning electron microscopy. Additionally, the average microhardness value of ceramic nanocomposite coatings fabricated from lithium sulphate–zirconium silicate bath is approximately 8.5 times higher than that of the as-received aluminium. The surface statistics of the coatings is discussed in detail to explain the roughness and related parameters for better understanding. These observations demonstrate the importance of surface statistics in controlling the morphology of the coatings and its properties. From the X-ray diffraction investigations, it can be concluded that the formed nanocomposite coatings are crystalline in nature and that the crystallinity of the coatings decreases with increasing applied current density.

Determinación de los mecanismos de fractura de un material multicapa de aluminio de alta resistencia y excelente tenacidad a impacto basado en la aleación aeroespacial Al 7075

An aluminium multilayer laminate has been processed by hot rolling. It is constituted by 19 alternated layers of high-strength aluminium alloy (Al 7075-T6, 82 % vol) and thinner pure aluminium layers (Al 1050-H24, 18 % vol). The microstructure of the constituent alloys and the composition gradient across the interfaces has been characterized. The multilayer laminate and the as-received aluminium alloys have been tested at room temperature by Vickers microhardness, three-point bend test and impact Charpy test. The outstanding improvement in damage tolerance, which is 18 times higher than that for the as-received Al 7075 alloy, is due to both intrinsic and extrinsic fracture mechanisms operating in the multilayer laminate during mechanical testing.

Characterization of sputtered Al-B-Si thin films produced with composite targets for device applications

AbstractSputtered films were deposited over glass and silicon (Si) substrates by using homemade centrifuged aluminum (Al) targets containing boron (B) AlB2 and AlB12 particles as their constituents. Additional films were produced with an as-received aluminum target for comparison purposes. The composite targets were mounted in the magnetron sputtering system working at varying discharge powers, ranging from 200 to 450 W, to produce films with the smallest surface roughness. This roughness analysis showed that films deposited from the composite targets (fabricated by centrifugal casting) possessed lower surface roughness than the pure aluminum films if they were deposited over silicon substrates. Also, preliminary studies of film structure and mechanical properties revealed that the films produced with the composite targets had smaller grain size, dominant compression stresses, higher disorder in the crystalline structure, and higher hardness and elastic modulus, when compared with the films produced with the pure aluminum target.

Laser surface alloying of aluminium with WC + Co + NiCr for improved wear resistance

In the present study, laser surface alloying of aluminium with WC+Co+NiCr (in the ratio of 70:15:15) has been conducted using a 5kW continuous wave (CW) Nd:YAG laser (at a beam diameter of 0.003m), with the output power ranging from 3 to 3.5kW and scan speed from 0.012m/s to 0.04m/s by simultaneous feeding of precursor powder (at a flow rate of 1×10−5kg/s) and using He shroud at a gas flow rate of 3×10−6m3/s. The effect of laser power and scan speed on the characteristics (microstructures, phases and composition) and properties (wear and corrosion resistance) of the surface alloyed layer have been investigated in details. Laser surface alloying leads to development of fine grained aluminium with the dispersion of WC, W2C, Al4C3, Al9Co2, Al3Ni, Cr23C6, and Co6W6C. The microhardness of the alloyed zone is significantly improved to a maximum value of 650 VHN as compared to 22 VHN of the as-received aluminium substrate. The mechanism of microhardness enhancement has been established. The fretting wear behavior of the alloyed zone was evaluated against WC by Ball-on-disc wear testing unit and the mechanism of wear was established.

On Hydrophobic and Icephobic Properties of TiO2-Doped Silicon Rubber Coatings

In the present work, flat and micro-/nano-rough water and ice-repellent coatings based on room-temperature vulcanized silicone rubber (RTV SR) incorporated with titania (TiO2) nanopowder as a dopant were prepared and investigated. Such water and ice-repellent coatings are potential candidates for protecting high-voltage equipment such as conductors and insulators. Supehydrophobic samples with contact angle (CA) >145o and contact angle hysteresis (CAH) ~5-10o were prepared by spin coating TiO2-loaded RTV SR suspensions on etched substrates. The SEM investigations of the sample surfaces revealed that the alumina filler (loaded into the as-supplied silicone rubber product) had some influence on the surface topographies of the prepared coatings. It was also found that the nanopowders used as dopants further increased the surface roughness (and correspondingly water repellency) of the coatings. While the TiO2-doped RTV SR demonstrates high CA and low CAH values, which is characteristic of the Cassie wetting regime, the wetting mode on the rough RTV SR coated sample with high CAH is expected to be a mixed Cassie-Wenzel regime. The anti-icing behaviour of the coating was studied under atmospheric icing conditions. Rough superhydrophobic coatings prepared with TiO2 nanoparticles of dielectric constant (~80) resulted in reducing the ice adhesion strength by at least ~7 times compared to a mirror-polished aluminium sample and by ~9 times compared to an as-received aluminium sample. At approximately -15 oC, water droplets were found to freeze on polished aluminium after approximately 5 s, while their freezing was delayed by as long as ~12-13 min on a superhydrophobic nanocomposite surface doped with TiO2 powder. This delay is explained by the insulating properties of the rough surface that entraps a significant amount of air into its structure. Therefore, the coatings prepared show promise for industrial applications on high-voltage equipment, including insulators, since they can reduce ice accumulation, while also reducing the risk of flashover on outdoor insulators.