Polished Aluminum Surface Research Articles

From Dataset Creation to Defect Detection: A Proposed Procedure for a Custom CNN Approach for Polishing Applications on Low-Performance PCs

This study focuses on training a custom, small Convolutional Neural Network (CNN) using a limited dataset through data augmentation that is aimed at developing weights for subsequent fine-tuning on specific defects, namely improperly polished aluminum surfaces. The objective is to adapt the network for use in computationally restricted environments. The methodology involves using two computers—a low-performance PC for network creation and initial testing and a more powerful PC for network training using the Darknet framework—after which the network is transferred back to the initial low-performance PC. The results demonstrate that the custom lightweight network suited for a low-performance PC effectively performs object detection under the described conditions. These findings suggest that using tailored lightweight networks for recognizing specific types of defects is feasible and warrants further investigation to enhance the industrial defect detection processes in limited computational settings. This approach highlights the potential for deploying AI-driven quality control in environments with constrained hardware capabilities.

Hybrid bilayer membranes on metallurgical polished aluminum

In this work we describe the functionalization of metallurgically polished aluminum surfaces yielding biomimetic electrodes suitable for probing protein/phospholipid interactions. The functionalization involves two simple steps: silanization of the aluminum and subsequent fusion of multilamellar vesicles which leads to the formation of a hybrid bilayer lipid membrane (hBLM). The vesicle fusion was followed in real-time by fast Fourier transform electrochemical impedance spectroscopy (FFT EIS). The impedance-derived complex capacitance of the hBLMs was approximately 0.61 µF cm−2, a value typical for intact phospholipid bilayers. We found that the hBLMs can be readily disrupted if exposed to > 400 nM solutions of the pore-forming peptide melittin. However, the presence of cholesterol at 40% (mol) in hBLMs exhibited an inhibitory effect on the membrane-damaging capacity of the peptide. The melittin-membrane interaction was concentration dependent decreasing with concentration. The hBLMs on Al surface can be regenerated multiple times, retaining their dielectric and functional properties essentially intact.

Microsecond Laser Texturing of an Aerospace Grade Aluminum Alloy to Synthesize Superhydrophobic, Anti-Water Clogging Surfaces

Traditionally superhydrophobic surfaces are prepared by applying liquid repellant organic coatings or nano-based coatings. These superhydrophobic coatings are prone to wear and can be easily damaged by abrasion and cleaning. Recently researchers are switching interest to more efficient and promising technology of pulse laser texturing for engineering sub-micron topographies to have superhydrophobic surfaces. In this research, the micro-second Laser Pulses are used to feature sub-micron textures on titanium nitride coated aluminum and polished aluminum surfaces in order to achieve the water contact angle greater than 150°. Titanium nitride coated aluminum surface with scan line separation of 50 µm shows superior hydrophobicity having a water contact angle of 156º. These superhydrophobic aluminum surfaces have applications for anti-water clogging and anti-corrosion use.

Superhydrophobic and Highly Oleophilic Polystyrene Fibers (PS) with Delayed Freezing Time and Effective Oil Adsorption

We present an efficient and simple approach for preparing superhydrophobic-superoleophilic polystyrene (PS) fibers via electrospinning. Bead-on-string fibers from a 5% PS solution and micro-sized fibers from a 20% PS solution were combined to achieve a surface having very high contact angle (about 160°) and low contact angle hysteresis. The presence of bead-on-string fibers increases the superhydrophobicity of the sorbent. The micro-sized PS fibers improve the mechanical properties of the electrospun mat through their elastic and flexible behavior. An evaluation of wettability at a low temperature (-10 oC) showed a delayed freezing time for water droplets on the superhydrophobic surface. Water droplets on a polished aluminum surface froze more quickly (about 6 seconds) than droplets on the fabricated superhydrophobic surface (about 500 seconds). Finally, the oil adsorption capacity of the developed superhydrophobic PS fibers, which have a porous surface structure, showed values of 69.1, 69.3 and 61.2 g/g for canola oil, olive oil and motor oil, respectively.

Creating highly wettable paper towel-like aluminum surfaces through tuned bulk micro-manufacturing

The contact angle (CA) of a water droplet on the polished aluminum surfaces is usually between 60° and 90°. This paper discusses a tuned bulk micro-manufacturing approach for transforming the surface topology of aluminum simultaneously at the micro- and nano-length scales, thereby significantly influencing its wetting characteristics. The approach is cheap, easy to implement, and scalable. The treated aluminum surfaces appeared like roughly polished surfaces at the macroscale and were found to be robust and non-toxic. They exhibited a paper towel effect by showing extreme surface wettability (CA of zero) to many industrial liquids, i.e., wetting on these surfaces is only a function of the surface roughness but not the fluid type. This extreme wetting ability to multiple liquids (or ultra-omniphilicity) was generated by sequentially creating a sub-surface micro- and nano-cavity architecture with nano-cavities within the embryos of micro-cavities interconnected by a network of micro-grooves.

Spreading of a distilled water droplet over polished and laser-treated aluminum surfaces

Spreading of a distilled water droplet over polished and laser-treated aluminum surfaces is studied experimentally. We present an attempt to apply the molecular-kinetic theory to the experimental dependences of the dynamic contact angle on the contact line speed. Advancing and receding contact angles at different liquid flow rates are obtained experimentally, and their values are used to calculate the contact angle hysteresis on each substrate. The bottom-up approach is used to form a droplet on the surface when liquid is supplied through an opening in the substrate. This makes it possible to control wetting and dewetting by increasing and decreasing the droplet volume. The main geometrical parameters are obtained using the shadow method by Axisymmetric Drop Shape Analysis-Profile. Experimental data on the dynamic contact angle on a laser-treated surface are found to be a better fit to the theoretical equation in comparison with the results on a smooth polished surface. We have formulated a hypothesis that the theoretical and experimental values of the dynamic contact angle are in good agreement due to the physics of the process (smaller hysteresis on the laser-treated surface).

Erratum to: Effect of heterogeneity on hydro/ice-phobic properties of alkylsilane/fluoro-alkylsilane-based coatings on Al substrates

In this work, hydrophobic and anti-ice performances of heterogeneous coatings (HCs) were studied. Multilayer thin films of homogeneous and heterogeneous chemically different alkylsilane compounds, i.e., octadecyltrichlorosilane (OD) and 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PF) were fabricated by alkylsilane/fluoro-alkylsilane deposition on a flat aluminum alloy (AA6061) substrate. The contact angle (CA) values for the homogeneous coatings of OD–OD and PF–PF after a 12-h immersion time (IT) were ~140° and ~120°, respectively. However, significant improvements in CA values were observed for the HCs, PF–OD and OD–PF, with CA values of ~154° and ~160°, respectively, for a 12-h IT. Moreover, very small contact angle hysteresis (CAH) values of ~6°–7° were obtained for PF–OD and OD–PF, whereas large CAH values of ~40°–65° were obtained for the homogeneous coatings. Scanning electron microscopy of the coated surfaces showed a rough structure at the micro-/nano-meter scale and X-ray photoelectron spectroscopy analysis indicated the presence of alkylsilane and/or fluoro-alkylsilane molecules on polished aluminum surfaces. The ice adhesion reduction factor (ARF) of OD–OD and PF–PF homogeneous coatings shows that ice adhesion strength is about 1.5 and 1.7 times lower, respectively, than that obtained on a polished bare Al sample. However, the ARF of PF–OD and OD–PF HCs shows that ice adhesion strength is about 2.7 and 3.5 times, respectively, lower than that obtained on a polished bare Al sample.

Experimental study of geometrical characteristics of distilled water and aqueous ethanol solution droplets evaporating on aluminum surface

Change of geometrical characteristics of distilled water and aqueous ethanol solution droplets was studied under their evaporation on aluminum surface. According to change in the contact diameter three evaporation modes of distilled water droplet on polished aluminum surface were detected: increase in the contact area, pinning of a droplet (constant contact area), and droplet depinning (decrease in the contact diameter). During evaporation of aqueous ethanol solution droplets, two evaporation modes were detected: increase in the contact area, and droplet depinning.

Hydrophobic and ice-phobic properties of self-assembled monolayers (SAMs) coatings on AA6061

The effects of alkyl chain length and immersion time (IT) on hydrophobic and ice-phobic properties were investigated through self-assembled monolayers of alkylsilane molecules, i.e. OT (trichloro-octylsilane) and OD (trichloro-octadecylsilane) on a flat aluminum alloy (AA6061) substrate. By increasing IT, the wetting behavior of the coatings, characterized by contact angle (CA) and contact angle hysteresis (CAH) measurements at room temperature, showed an enhancement of hydrophobic properties. However, the effect of IT on wetting properties was more significant in the case of the sample coated with longer alkyl chains (OD) than that with short alkyl chains (OT). Icing tests showed delayed ice formation and lower adhesion strength on samples with larger CA values and smaller CAH values. The scanning electron microscopy images of the coated surfaces showed the rough structure at micro/-nanometre scale on a polished aluminum surface. X-ray photoelectron spectroscopy (XPS) analysis of the coated samples showed the presence of more alkylsilane molecules when IT was increased from 15 min to 12 h.

An impact regime map for water drops impacting on heated surfaces

The impact morphology of millimetric water drops on a polished aluminium surface has been studied experimentally by high-speed imaging, for surface temperatures between 50 and 400°C, and Weber numbers up to 160. Five impact regimes are defined based on the final outcome of the impact: three independent regimes (secondary atomisation, rebound, and splashing), and two mixed regimes (rebound with secondary atomisation and splashing with secondary atomisation). Impact regimes are displayed on a quantitative two-dimensional map, having the surface temperature and the impact Weber number at ambient conditions as coordinates. Some characteristics of the transition boundaries between impact regimes are discussed.

Superhydrophobic nanocomposite surface topography and ice adhesion.

A method to reduce the surface roughness of a spray-casted polyurethane/silica/fluoroacrylic superhydrophobic nanocomposite coating was demonstrated. By changing the main slurry carrier fluid, fluoropolymer medium, surface pretreatment, and spray parameters, we achieved arithmetic surface roughness values of 8.7, 2.7, and 1.6 μm on three test surfaces. The three surfaces displayed superhydrophobic performance with modest variations in skewness and kurtosis. The arithmetic roughness level of 1.6 μm is the smoothest superhydrophobic surface yet produced with these spray-based techniques. These three nanocomposite surfaces, along with a polished aluminum surface, were impacted with a supercooled water spray in icing conditions, and after ice accretion occurred, each was subjected to a pressurized tensile test to measure ice-adhesion. All three superhydrophobic surfaces showed lower ice adhesion than that of the polished aluminum surface. Interestingly, the intermediate roughness surface yielded the best performance, which suggests that high kurtosis and shorter autocorrelation lengths improve performance. The most ice-phobic nanocomposite showed a 60% reduction in ice-adhesion strength when compared to polished aluminum.

Adhesion of Biologically Inspired Oil-Coated Polymer Micropillars

This paper presents the performance of a beetle foot-hair inspired polymer microfibrillar wet adhesive. Micropatterned poly(dimethylsiloxane) arrays of low aspect ratio cylinders are fabricated using optical lithography and molding techniques. A thin layer of viscous silicone oil is applied via stamping. The synthetic micropillar wet adhesive is characterized with a custom tensile adhesion measurement setup by varying the retraction speed, preload, contact time, oil viscosity and oil volume. An enhancement of adhesion up to 25% over the same micropattern without any applied liquid is demonstrated on a smooth substrate. A thicker silicone layer is shown to increase the adhesion of the micropillars by a factor of almost 6 on a 650 nm root-mean-square rough slightly polished aluminum surface. A model is also developed that combines surface tension and dynamic viscous forces to predict the adhesive performance. This model matched experimental data with reasonable tuning of only a single parameter. These results are used to propose further advancements in the design and fabrication of synthetic wet micropatterned adhesives.

Emissivity characteristics of roughened aluminum alloy surfaces and assessment of multispectral radiation thermometry (MRT) emissivity models

Experiments were performed to examine the emissivity characteristics of aluminum alloy samples over the spectral range of 2.05 to 4.72 μm and temperatures of 600, 700 and 800 K. AL 1100, 7150, 7075 and 2024 samples were tested which possessed polished, 6- and 14-μm surface finishes. Additionally, extruded and saw-cut samples were tested to examine the effects of extreme roughness on emissivity. For the polished, 6- and 14-μm samples, the emissivity decreased appreciably between 2.05 and 3.5 μm, and increased slightly between 3.5 and 4.72 μm. Spectral variations were far less pronounced for the extruded and saw-cut surfaces. Eighteen MRT emissivity models were examined for accuracy in temperature measurement. Drastic changes in the emissivity distribution precluded the use of a single function to accurately represent every band of the measured spectrum. Overall, two relatively simple models provided the best overall predictions for different alloys and temperatures. These are the same models that yielded the best overall results for polished aluminum surfaces in a previous study by the authors. Despite the relative success of these models, this study points to a need to greatly enhance the measurement accuracy of radiation thermometers to meet the needs of the aluminum industry.

Ordered anodic alumina nanochannels on focused-ion-beam-prepatterned aluminum surfaces

A combined process of electropolishing, focused-ion-beam lithography, and controlled anodization is used to fabricate anodic alumina films with ordered nanochannels. The ion beam is used to create a hexagonally close-packed lattice of concaves on a polished aluminum surface and the concaves act as pinning points for guiding the growth of nanochannels in the following anodization step. By carefully matching the lattice constant (100 nm) with the anodization voltage, ordered nanochannels with aspect ratio of ∼100 are fabricated. The effects of the ion dose and its corresponding depth of the concaves on the ordering of the nanochannel array are investigated and a minimum depth of 3 nm is found to be necessary for effective guidance of the growth of ordered nanochannels.

Parameters controlling solidification of molten wax droplets falling on a solid surface

An experimental study was done to identify parameters that determine the shape of splats formed by droplets of paraffin wax impacting and freezing on a polished aluminum surface. Impact velocity was varied from 0.5 to 2.7 m/s and surface temperature from 23 to 73 °C. Droplet impact was photographed, and the splat diameter and liquid-solid contact angle measured from photographs. A simple energy conservation model was used to predict the maximum extent of droplet spread and the rate of droplet solidification. The extent of droplet solidification was found to be too small to affect droplet impact dynamics. Photographs showed liquid recoiling in the droplet center following impact on a cold surface (23 °C); the height of recoil diminished if either substrate temperature or impact velocity was increased. Droplet recoil was attributed to surface tension pulling back the periphery of the splat. Reducing the surface temperature increased surface tension, promoting recoil. At sufficiently large impact velocities droplets fragmented. A model based on the Rayleigh-Taylor instability was used to predict the number of satellite droplets that broke loose after impact.

An atomic force microscopy study of the effect of surface roughness on the fracture energy of adhesively bonded aluminium

The effect of roughening an initially polished aluminium surface using the Forest Products Laboratory chemical etch on the adhesive joint strength has been determined. It was found that while the lap shear strength increased rapidly with etching for short times, the fracture energy did not increase significantly until etching had occurred for at least 15 min. An atomic force microscope (AFM) was used to study the surface/interface morphology and to quantify the surface roughness. The AFM images showed that etching occurs heterogeneously across the aluminium surface and a correlation was found between the fracture energy and the fraction of etched surface. A model based on Griffith's fracture energy approach has been proposed to explain this observation. The lap shear strength was found to be more sensitive to a finer scale roughness which is generated at shorter etching times. Other observations regarding the mode of fracture and the variability in joint strength as a function of the surface roughness are explained on the basis of varying stress concentrations at the crack tip.

On the nature of the mechanically polished aluminium surface

The effect of mechanical polishing of aluminium, using a final polish with 0.5 μm-Al 2O 3 in water, has been examined by transmission electron microscopy. Whilst the polished surface is relatively flat, about 10% of the exposed surface contains embedded Al 2O 3 constituting a newly-introduced major surface inhomogeneity with implications in consequent corrosion studies.

The effect of surface characterization and laser beams polarization on laser Doppler vibrometry

In a laser Doppler vibrometry, the characterization of the measured surface plays an important role in both in-plane and out-of-plane surface motion measurements. Experimental data is presented for the in-plane optical probe configuration, where the vibrating surface is illuminated symmetrically by two laser beams. However, some of the conclusions of the present study apply also to out-of-plane vibration measurements. It is found that certain surfaces perform better than others. How the surface character affects the in-plane surface motion measurement (in particular, the signal-to-noise ratio and the probe alignment) is studied. The surfaces studied are lathe-finished, polished aluminum and steel surfaces and two types of retroreflecting tapes from 3M company. Also, the profiles of the metallic surfaces are obtained with a profilometer. A simple model is used to relate the surface characteristics to the performance of in-plane motion measurement. The effect of polarization of the two laser beams is also studied, including the depolarization of the light by the surface. [Work supported by ONR.]

Frictional characteristics of resilient lining materials.

The frictional characteristics of 7 resilient (soft) denture liners and acrylic resin denture base material have been evaluated against a polished aluminium surface and simulated oral mucosa (silicone impression material). Friction studies were performed with and without distilled water as a lubricant. The friction measured for denture base acrylic was lower than that for the liners under all conditions. The friction observed with soft liners decreased with longterm water sorption and through lubrication. The observed friction effects arose from the mechanical properties of the liners as well as the conformation of the liners with the test substrate, both of which are affected by longterm water sorption.

Transient reflectivity behavior of pure aluminum at 10.6 μm

Time-resolved measurements of specular reflectivity of polished pure aluminum surfaces subjected to intense 10.6-μm pulsed-laser radiation in vacuum are reported. A sharp decrease in reflectivity to an anomalously low value (35%) was observed midway in the pulse followed by nearly complete recovery of full reflectivity near the end of the pulse. The peak-power-density threshold for this phenomenon was found to agree with the intrinsic surface melt threshold as determined from numerical heat-transfer calculations and microscopic examination of the samples.