Hard Anodizing Process Research Articles

Effect of pulse current on surface properties of aluminum oxide coating containing graphite

Anodizing is widely used as a surface treatment for aluminum alloy to improve its surface properties by increasing the thickness of the oxide layer. Generally, conventional anodizing by direct current (DC) produced high porosity and micro‐cracks. Utilizing pulse current (PC) as a power source and graphite particles as reinforcement for the oxide layer may solve these problems. Therefore, the present work aims to study the effect of the combination approaches on coating growth and the surface characteristics of the oxide coating. The graphite‐incorporated composite oxide coating on the AA2017‐T4 Al alloy was developed by DC and PC hard anodizing process. The surface morphology, topography, chemical composition, and surface hardness were evaluated. In PC anodizing, the growth rate of oxide layer was slower (0.59 μm/min) than DC anodizing (1.08 μm/min). The surface pores start to develop at the 30th minute compared to DC, which is the 20th minute. At 60 min, the formation of porous composite oxide coating is complete with pore dimension (width: 46.74 ± 19.96 μm and depth: 7.11 ± 2.57 μm) and thickness of 35.20 ± 8.90 μm for PC, whereas for DC pore dimension (width: 81.03 ± 21.60 μm and depth: 17.16 ± 4.31 μm) and thickness of 64.80 ± 23.69 μm. Surface roughness and hardness of composite oxide coating by PC were measured at about 1.90 ± 0.04 μm and 379.10 ± 4.37 HV, respectively. Meanwhile, the DC reveals a significant increase in roughness (4.28 ± 0.25 μm) and a decrease in hardness (302.75 ± 1.09 HV). The introduction of graphite particles with PC anodizing reduces the surface porosity, microcracks and enhances the surface hardness of oxide coating.

The Effect of Electronic Properties of Anodized and Hard Anodized Ti and Ti6Al4V on Their Reactivity in Simulated Body Fluid

The electronic properties of barrier and porous layers on Ti and Ti6Al4V were studied. Barrier anodic oxides grown to 40 V on Ti and on Ti6Al4V are both n-type semiconductors with a band gap of 3.3 eV and 3.4 eV respectively, in agreement with the formation of amorphous TiO2. Anodizing to 200 V at 20 mA cm−2 in calcium acetate and β-glycerol phosphate disodium pentahydrate leads to the formation of Ca and P containing porous films with a photoelectrochemical behaviour dependent on the metallic substrate. A band gap of 3.2 eV and the flat band potential of −0.5 V vs Ag/AgCl were measured for the porous oxide on Ti, while optical transitions at 2.15 eV and a significantly more positive flat band potential were revealed for the porous oxide on the alloy. The different electronic properties were rationalized by taking into account the presence of localized states inside the gap, induced by incorporation of Al and V from the underlaying alloy during the hard anodizing process. These electronic properties are responsible of the reactivity of porous layer grown on Ti6Al4V alloy in simulated body fluid.

Anodized Aluminum Surface with Topography-Mediated Antibacterial Properties.

Topography-mediated antibacterial surfaces that inactivate bacteria by physical contact have gained attention in recent years. Contrary to conventional antibacterial coatings, topography-mediated antibacterial surfaces do not suffer from coating instability and possible toxicity problems. In this study, a one-step hard anodization process has been deployed to fabricate a topography-mediated antibacterial aluminum surface. By optimizing anodization parameters, such as the concentration of the electrolyte, current density, and anodization time, desirable features of micronanoscale morphology were achieved. The optimum conditions of anodized aluminum that provided pores of a diameter of 151 ± 37 nm effectively killed 100% of E. coli bacteria.

Tuning of the Mg Alloy AZ31 Anodizing Process for Biodegradable Implants.

Coatings were grown on the AZ31 Mg alloy by a hard anodizing process in the hot glycerol phosphate-containing electrolyte. Anodizing conditions were optimized, maximizing corrosion resistance estimated by impedance measurements carried out in Hank’s solution at 37 °C. A post anodizing annealing treatment (350 °C for 24 h) allowed us to further enhance the corrosion resistance of the coatings mainly containing magnesium phosphate according to energy-dispersive X-ray spectroscopy and Raman analyses. Gravimetric measurements revealed a hydrogen evolution rate within the limits acceptable for application of AZ31 in biomedical devices. In vitro tests demonstrated that the coatings are biocompatible with a preosteoblast cell line.

Thermovision study on Alumina’s Ra v/s Ts for AIDHVACS to control COVID-19

The current study is the authors’ next work from the thermo vision perspective of real time single sun solar field performance infrared thermography (IRT) on commercial grade Alumina solar absorber surface coatings (SASCs) to recognize surface roughness (Ra) as one of the important production process parameters. In a previous study, it was investigated with IRT, and found that Ra<1.8 is favorable and hard anodized Alumina (HAAO) coatings exhibits better surface temperature (Ts) gain as compared to organic dyed non-HAAO coatings on Aluminum substrate, and are more stable in solar field for many years in open air environment without degrading their performance. It may be useful in better optimization of SASCs specifically for personal protective equipments (PPEs) sanitization and artificial intelligence (AI) driven heating ventilation air conditioning (HVAC) systems (AIDHVACS) design to control Covid-19 in current situations.The influence of Ra of few microns ∼ <15 µm on Alumina SASCs’ Ts gain is examined. The presented study shows that more than 1.05 mm thickness of substrate flat is necessary to develop good quality of alumina coating; Ra<1.8 µm is favorably expected to the extent of Ra value approaching as close as to nanoscale ∼ 5-500 nm; local surface temperature gained is depending upon local Ra profile as well as upon surface morphology in addition to the anodizing process parameters and other environmental factors. It suggests that the optimal surface profile should be designed as an integral to the production line processes. The substrate surface chemical composition may also change while processing due to surface contact with the processing tools, which may also result in altered solar field performance due to substrate altered material composition prior to hard anodizing process, as examined with X-ray fluorescence spectrometry (XRF) and ultraviolet–visible spectrophotometry (UV-VIS). The novelty is that other studies of surface roughness parameter is focused upon convective heat transfer inside tunnel or duct solar heat absorbers e.g. air heaters, whereas the authors have focused upon surface roughness of solar radiation receiving outer surface as an important commercial production process variable having effect upon conductive heat transfer in solar thermal power systems. The AIDHVACS needs machine learning and big data analysis as the need of the hour.

Friction and Wear Response of a Hard-Anodized AA6082

The properties of anodized aluminum, and wear resistance in particular, are of high interest for the scientific community. In this study, discs of AA6082 were subjected to a peculiar hard anodizing process leading to anodized samples having different thicknesses. In order to investigate the wear mechanism of samples, unidirectional tribological tests were performed against alumina balls (corundum) under different loading conditions. Surface and microstructure of all the samples were characterized before and after the tribological tests, using different characterization techniques. The tribological tests showed remarkable differences in the friction coefficient and wear behavior of the anodized AA6082 samples, related to the microstructure modifications and to the specific applied sliding conditions.

Characteristics and tribological behavior of the hard anodized 6061-T6 Al alloy

Abstract The hard anodizing process is one of the best choices to achieve high wear resistance in a 6061-Al alloy, which is commonly used in marine and aerospace applications. In this study, the hard anodizing process was performed by applying several current densities at different times. Two types of electrolytes containing various concentrations of sulfuric acid or oxalic acid were used as the bath. The microhardness of the coatings was measured. Morphology, thickness, and structure of the samples were investigated through a scanning electron microscope (SEM), and an X-ray diffractometer (XRD). Surface roughness and tribological behavior of the optimum samples were also examined. The results revealed that there was an optimum value for the electrolyte concentration, as well as the hard anodizing current density and time at which the hardest coating was obtained. All the oxide films had an amorphous structure. Doing the hard anodizing at 35 mA/cm2 in a sulfuric acid bath for 50 min resulted in a uniform and crack-free coating. The weight loss of this oxide film was 50 and 21 times lower than the substrate and the coating obtained in an oxalic acid bath at the optimum conditions, respectively.

Anodic alumina oxide surfaces prepared by dual hard and mild anodization at subzero temperature: Surface microscopic characterization and influence on wettability

Multistage anodizations allow the preparation of new generations of ordered anodic alumina oxide porous structures with large interpore distances, yet the influence of second anodization and pore widening times on pore dimensions and wettability of the obtained structures has not yet been fully studied. The main objective of this study was to characterize the obtained pores (dimensions and morphology), for different anodizations and pore widening times, and to investigate their respective influence on surface wettability. Anodic alumina oxide ordered porous surfaces were prepared using a dual hard and mild anodization process with oxalic and phosphoric acids at subzero temperature, with or without pore widening. Statistical analyses were realized on pore measurements from samples produced with a large range of anodization durations (7 different tested times). The obtained surfaces possessed regular ordered pores of 99 nm and 307 nm for respectively median pore diameter and inter-pore distance, before pore widening, and did not conform to expected theoretical values for either usual lone mild or hard anodization conditions. The slow growth of pore depth (median of 11 nm/min) observed during second anodization could be explained by the subzero electrolyte temperature used. Pore widening effectively increased pore diameter, but had statistically a bigger impact on diameters for shorter second anodization time than for longer ones. Also, pore widening significantly decreased pore depth as well as the oxide barrier thickness. Additionally, porosity increased from 9.57% to 14.8% after 3 hours of pore widening, but did not significantly affect surface wettability, which was however increased when compared to flat control surfaces. The obtained results showed that a dual anodization with different electrolytes at a subzero temperature had a significant impact on pores dimensions. A discussion on the respective effects of surface chemistry and surface roughness in the wetting evolution was proposed.

Dry Sliding Tribological Properties of a Hard Anodized AA6082 Aluminum Alloy

The applications of aluminum and its alloys are still limited by low hardness and low wear resistance properties. Surface modifications, such anodizing and plasma electrolytic oxidation, represent a feasible way to overcome these drawbacks. In this study, discs of AA6082 were subjected to the so-called G.H.A. hard anodizing process leading to an anodized layer having a honeycomb-like structure. Samples having alumina layer thicknesses of 10, 50 and 100 μm were subjected to unidirectional dry sliding wear tests, using bearing steel and silicon nitride as counterbody materials. Surface and structure characterization of the samples were performed before and after the tribological tests, using a wide range of techniques; atomic force microscopy and scanning electron microscopy techniques were used before the wear tests. The wear scars were characterized by scanning electron microscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopy techniques. Results show that the different thickness of the anodized layer does not affect the pores dimensions but has an influence on the micrometric domains in which the pores are divided. These features coupled with the wear test conditions, show to have a strong influence on the wear behavior. The thinnest sample showed also the best performance against the ceramic counterbody.

Pengaruh Rapat Arus Proses Continuous Hard Anodizing Elektrolit (H2SO4) terhadap Laju Korosi Pipa Aluminium 6061 dengan Pengujian Kabut Garam

Anodizing is an electro-chemical process used to coat metal surfaces with a stable oxide layer. The function of this oxide layer is to increase corrosion resistance. The purpose of this study is determine the effect of variations in current density on the continuous hard anodizing process carried out in sulfuric acid electrolyte solution (H2SO4) on the corrosion rate of aluminum alloy 6061. Corrosion rate testing is carried out through salt fog testing. The values of the current variation used are 1 A/dm2; 2 A/dm2; 3 A/dm2; 4 A/dm2; and 5 A/dm2. Statistical calculations using the analysis of variance proved the current density in the anodizing process has a significant effect on the corrosion resistance of the anodizing workpiece. Corrosion testing provides information that the highest corrosion rate is an anodizing workpiece with a current density of 1 A/dm2, which is 125.6861 mdd, then 2 A/dm2 of 104.33333 mdd. The lowest corrosion rate value obtained at the use of current density 3 A/dm2, that is 51,8083 mdd. Meanwhile, the use of current density of 4 A/dm2 has a slightly higher corrosion rate compared to the use of current density of 3 A/dm2, which is 86.5444 mdd. Furthermore, the use of current density of 5 A/dm2 has the highest decay rate, so that the formed oxide layer will be damaged, as seen from the higher corrosion rate of the material, which is 100.8361 mdd.

Combined mild and hard novel fabrication approach for nanoporous membrane

Anodization of aluminum by a hard anodizing or mild anodizing process is usually done to obtain metal top surface finishing. Recently, this process has been becoming famous for the formation of through-hole porous oxide membranes (TH-POM) which act as a template for fabrication of nanowires/tubes. Membranes with different pore diameters, interpore distance, depth of pore and porosity can be obtained by selecting different parameters such as type and concentration of electrolyte, pH, temperature, time and applied voltage. In this research paper, exclusive experiments were studied and conducted to obtain TH-POM which will be template for generation of ordered nanowires by an electrochemical process. This research is carried out using a combination of mild anodization (MA) and hard anodization (HA) with novel heterogeneous control parameters by using DC power supply, magnetic stirrer and data acquisition system (DAQ) and at high temperature in order to minimize the refrigeration cost required for cooling the electrolyte. Excellent ordered membranes of 24–29 nm and 40–50 nm pore diameter were obtained in short time, characterized by SEM and EDS and analyzed by I–V curves obtained using an Arduino-based current/voltage data logger. A thermal stress test is also performed on the TH-POM formed using MA and HA.

Hard Anodizing of Aerospace AA7075-T6 Aluminum Alloy for Improving Surface Properties

In the current research work undertaken, an oxide film was grown by performing hard anodizing process on a pure aluminum layer deposited by PVD magnetron sputtering process on AA7075-T6 alloy. The corresponding tribo-mechanical properties were evaluated and compared with those of the base alloy. The dry sliding wear experiments were carried out to investigate wear resistance of anodized AA7075-T6 against the AISI SS316 counter-body by means of a reciprocating tribo-testing setup. The hardness of AA7075-T6 after the anodizing process exhibited an enhancement of about 1.94 times. Results revealed that the wear of anodized coating was exceptionally less when compared with the substrate. Based on morphology and chemistry changes of worn-out surfaces and debris, it was determined that severe abrasive and oxidative wear was the primary wear mechanism for AA7075-T6. The anodizing process increased the friction coefficient from 0.33 to 0.46 but reduced the wear severity by altering the wear mechanism into mild polishing and abrasion. Anodizing enhanced the wear resistance of AA7075-T6 to about three times, and the wear rate decreased to around 4.3 times.

Tribological Properties of Oxide Coatings Produced on EN AW-5251 Alloy using Different Distances between Electrodes

Abstract The subject of the presented work was the analysis of the influence of the distance between the electrodes using in the coating process on the tribological properties of oxide coatings. Oxide coatings were prepared on EN AW-5251 aluminum alloy samples. The samples surfaces were subjected to hard anodizing process in a multicomponent electrolyte based on sulfuric acid with an addition of organic acids. Anodizing was carried out with a constant electric charge density of 180 A·min/dm2. The distances between the electrodes for subsequent samples increased every 0.125 m up to 1 m. The tribological partner in a sliding couple with oxide layers was pin of PEEK/BG. Tribological tests were conducted on a T-17 tester in reciprocating motion, in technically dry friction conditions. Before and after tribological test, examination of the geometrical structure of counter-specimens’ surface was carried out using the Form Talysurf contact profilographometer, via a 3D method. The most satisfactory tribological parameters were obtained for the PEEK/BG association with the coating produced at a distance between the electrodes equal to 0.25 m.

Microstructural and tribological investigations of diecast and hard anodized AlSiCu alloys

This work is aimed to understand the impact of the surface characteristics of diecast Al-Si-Cu alloy on the hard-anodizing process. High-pressure die-cast plates made of AlSi9Cu3(Fe), AlSi11Cu2(Fe) and AlSi12Cu1(Fe) alloys were hard anodized in as-diecast condition and after sandblasting and surface milling operations.The thickness and morphology of the anodic layer were investigated using optical and electron microscopy, whereas the tribological properties were evaluated using a reciprocating sliding testing machine under ball-on-flat configuration. The removal of both external eutectic Si segregation and oxide passivating layer due to milling operation is beneficial to increase the thickness of the anodic film, independently of the investigated alloy. However, this leads to a decrease of the abrasion resistance due to the presence of coarser Si particles. Sandblasting removes lower amounts of material and its effect on the anodizing response is more affected by the initial chemical composition of the alloy. The thickness of the oxide layer over the as-diecast surfaces increases by increasing the eutectic fraction and decreasing the Cu content. The greater the amount of α-Al phase in the surface microstructure, the thicker the anodic layer will be. Fine and globular eutectic Si particles lead to a thicker hard anodic layer respect to coarser and plate-like ones. The anodizing response seems in any case to be more related to the amount of α-Al matrix than the shape of Si particles. Higher eutectic fraction with globular eutectic Si particles is useful to increase the tribological properties of the anodic film. Lower eutectic amounts lead to increase the thickness of the anodic film but also to decrease the abrasion resistance.

Tribological Properties of the Oxide Coatings Produced onto 6061-T6 Aluminum Alloy in the Hard Anodizing Process

The aim of this work was to establish the influence of the thickness of the anodic coatings on their mechanical properties and to understand the relation between their hardness and the abrasion resistance. The coatings were produced in the hard anodizing process onto the 6061-T6 aluminum alloy. Their thickness was in the range between 19 and 43 µm. The abrasion resistance was determined by using Taber abrasion test. The weight losses of the coatings obtained were in the range between 15 and 11 mg and decreased with their increasing thickness. It has been shown that the hardness measured on the cross sections of the coatings did not correspond to their abrasion resistance. Thus, the new approach has been proposed. The hardness of the coatings was estimated on the basis of the results of the scratch test performed at the constant load. The results obtained correspond to the abrasion resistance of the coatings.

An Effect of Process Parameters to Anodic Thickness in Hard Anodizing Process

The anodizing process is an aluminum surface treatment process which an aluminum oxide film forms on an aluminum substrate. Typically, the anodic thickness is a required specification which depends upon current density and anodizing cycle time. In addition, another important factor is ramp time which must be proper set to prevent a burn defect. Thus, this paper investigates a relationship among these three factors to determine the setting condition which minimizes the anodizing cycle time. Moreover, the required thickness must be obtained without increasing the burn defect rate. The experimental design technique is proposed to achieve this goal and it is found that the current of 35 amp, ramp time of 340sec and anodizing time at 1400 sec ensure the obtained anodic thickness greater than 30 micron.

Self-Organization Process of Aluminum Oxide during Hard Anodization

The self-organization process of the porous anodic alumina (PAA) during hard anodization (HA) was proposed by synthetically investigating the nanopore morphology, the current density and barrier layer evolution of the PAA films, which were anodized in 0.3M oxalic acid at 150V (the voltage rising from 40V to 150V at the beginning). It was found that the high enough current density in the voltage rising stage can induce the fast film growth, which caused the pores to rapidly enlarge themselves and to reach a relatively ordered rearrangement. The barrier layer thickness showed linearly increase in voltage rising stage and then increased with a decelerated speed in the followed constant anodization stage, where the pores with growth advantage moved down straightly and gradually expanded their cell size to replace the inferior pores around. Accordingly, HA is a unequilibrium process and can be divided into two stages: I, the rapid pore enlargement and rearrangement during voltage rising stage, where the oxidation rate is larger than that of dissolution; II, competing growth of the nanopores during the followed constant voltage anodization, where the oxidation and dissolution rates approach to each other due to the thickened barrier layer. These findings are very helpful for more efficiently controlling the hard anodization process and developing new electrolyte systems to further broaden the interpore distance range.

Impedance spectroscopy of the process of hard anodizing of aluminum alloys

This article discusses an in situ method for the diagnostics of the hard anodizing process based on impedance spectroscopy allowing the coating thickness during treatment to be estimated. The experimental results are given for the hard anodizing of aluminum alloys used in the aircraft industry. Parameters of an equivalent circuit of the electrolyzer were specified and the regularities of their evolution were established. A diagnostic model was proposed and its efficiency was demonstrated for an industrial serial production.

Pulsed current effect on hard anodizing process of 2024-T3 aluminium alloy

Abstract This work focused on studying the effects of different electrical parameters on the hard anodizing process (in sulphuric acid bath) of AA 2024-T3, an important heat treated aluminium alloy which has several engineering applications in aerospace, motorsport and automotive fields due to its significant combination of high mechanical properties and low density. Hard anodizing treatment is here crucial for increasing both corrosion and abrasion resistance, but the presence of typical intermetallic precipitates makes the obtainment of a performing non-defective oxide difficult. Different anodizing procedures in direct current (DC), multistep direct current (MSDC), pulsed current (PC) (slow square pulse mode) and their appropriate combination (DCP PC modality induced a moderate loss in mechanical performances in all the different duty cycles experimented, while an extremely low defected oxide was obtained with a duty cycle of 50%. Proper merge of a soft and long initial DC current step followed by a suitable balanced final stage in PC allowed to obtain an interesting combination of significant hardness (> 340 HV) in parallel with a good oxide defectiveness state.

Morphology of anodic alumina films obtained by hard anodization: Influence of the rate of anodization voltage increase

The influence of the anodization voltage ramp on the morphology and thickness homogeneity of porous anodic alumina films was studied. The samples were prepared in the oxalic acid at 120 V during the hard anodization process. As a nondestructive characterization method, the smallangle Xray scattering technique was used. The analysis of diffraction patterns allows determining the mean value and dispersion of interpore distance and the channel tortuosity with high accuracy. The increase of voltage ramp at the initial stage of hard anodization process was shown to lead to reduction of mechanical deformation (tortuosity) of anodic alumina film during crystallization.