Phosphoric Acid Anodizing Research Articles

Structure and properties of the hot pressing molded anodized aluminum alloy/polyformaldehyde hybrids

The metal-plastic hybrid is one of the important solutions for lightweight and high-strength composite. The anodized aluminum alloy（AAA）/polyformaldehyde（POM） hybrids with excellent mechanical properties were processed by the hot pressing technology. The surface of the aluminum alloy plate was firstly pretreated with phosphoric acid and oxalic acid anodizing, resulting in a large number of micro-nano scale pores on the surface. These pores were well embedded with plastic melt during hot pressing to form micro-nano mechanical interlocking structures and the Al–O–C chemical bond at the interface is generated, thus ensuring good bonding strength at the metal and plastic interface. The maximum tensile-shear strength of the metal-plastic hybrid was 30.65 MPa, meanwhile, the metal-plastic interface failure presented mainly a mixed failure mode, including resin removal from the metal surface and plastic tearing from the plastic surface. At the same time, the salt spray test, thermal shock test, and variable temperature test were adopted to investigate the application performance of the metal-plastic hybrid. The Al/POM hybrids were able to maintain their mechanical strength above 20 MPa for 28 days in a salt spray environment, 14 times in a thermal shock cycle, and at high temperatures. The high mechanical strength of hybrid has good potential for automotive applications.

Isotopic Tracer Study of Initiation of Porosity in Anodic Alumina Formed in Chromic Acid.

In this paper, we focused on the initiation of porosity in the anodic alumina under galvanostatic conditions in chromic acid, using an 18O isotope tracer. The general concept of the initiation and growth of porous anodic oxide films on metals has undergone constant development over many years. A mechanism of viscous flow of the oxide from the barrier layer to the pore walls has recently been proposed. In this work, two types of pre-formed oxide films were analysed: pure Al2O3 formed in chromic acid, and a film containing As ions formed in a sodium arsenate solution. Both were anodized in chromic acid for several different time durations. Both pre-formed films contained the oxygen isotope 18O. The locations and quantities of 18O and As were analysed by means of ion accelerator-based methods supported by transmission electron microscopy. The significant difference observed between the two oxide films is in the 18O distribution following the second step of anodization, when compared with galvanostatic anodization in phosphoric or sulfuric acid reported in previous works. From the current experiment, it is evident that a small amount of As in the pre-formed barrier layer appears to alter the ionic conductivity of the film; thus, somehow, it inhibits the movement of oxygen ions ahead of advancing pores during anodization in chromic acid. However, anodising pure alumina film under these conditions does not enhance oxygen movement within the oxide layer. In addition, the tracer stays in the outer part of the growing porous oxide film. A lower-than-expected value for pure alumina enrichment in 18O in the pre-formed films suggests, indirectly, that the pre-formed film may contain hydrogen species, as well as trapped electrons, since no Cr is detected. This may lead to the presence of space charge distribution, which has a dual effect: it both retards the ejection of Al3+ ions and prevents O2- ions from migrating inward. Thus, the negative- and positive-charge distributions might play a role in the initiation of pores via a flow mechanism.

Surface Treatments for Enhancing the Bonding Strength of Aluminum Alloy Joints.

Aluminum alloy adhesive bonding joint widely appears in many industrial products. Improving the mechanical performances of aluminum alloy bonding joints has been attracting much effort. To acquire more excellent bonding strength, this paper focused on the effects of different surface treatments, including laser ablation and milling superposed by phosphoric acid anodizing (PAA). The treated surfaces were characterized by roughness and contact angle, and the effects of the geometric parameters of microstructures on wettability, failure mode, and shear strength were examined. The results indicate that those surfaces where the spacing is smaller than the diameter present a hydrophilic property and the corresponding specimens are mainly subject to cohesive failure, and vice versa. Additionally, laser ablation with a properly designed dimple pattern can greatly improve the bonding strength, and the maximum average shear strength of specimens with a thickness of 50 μm reaches 32.82 MPa, which is an increase of 28.15% compared with the original milling specimen. Moreover, fabricating groove or grid patterns on the surfaces and applying PAA treatment can also significantly enhance the bonding strength, reaching up to 36.28 MPa.

Effect of combination of microstructure and surface treatment on shear strength of precision bonded joints

ABSTRACT To improve the bonding strength of precision adhesive joints, mechanical and electrochemical surface treatments were combined to modify the original bonding surfaces. Microgrooves with different aspect ratios were manufactured on aluminum-alloy surfaces and phosphoric acid anodizing (PAA) was then applied to the surfaces. Wettability, shear strength, and fracture morphology were tested and analyzed. PAA treatment could change the original flat surface to be hydrophilic, and microgrooves could further enhance these characteristics. Compared with the original flat surface, the shear strength of the micro-structured surfaces without PAA treatment increased by 8.54% at an aspect ratio of 0.02, but decreased by 0.22% and 1.90% as the aspect ratio increased to 0.04 and 0.08, respectively. The shear strength of the flat surface only treated by PAA increased by 22.88%, while combining microgrooves could further improve the shear strength by 38.17%, 39.09%, and 42.24% at aspect ratios of 0.02, 0.04, and 0.08, respectively. Fracture morphology analysis and observation of interfacial wetting indicated that manufacturing microgrooves and applying PAA treatment on the aluminum-alloy surfaces could eliminate many tiny interface failures and greatly increase the effective bonding area, which significantly improved the shear strength.

An experimental and simulation study of RGO effects on mechanical behaviour of structural adhesive and lap shear joints strength

The research investigates the effects of adding Reduced Graphene Oxide (RGO) at various weight fractions (0.25, 0.5, 0.75 and 1 wt%) on mechanical properties of high strength structural adhesive Araldite©️ 2011 and lap shear strength of adhesive joints. For uniform dispersion of RGO across adhesive, an extensive solution mixing technique was carefully carried out for the preparation of RGO/Epoxy combinations. Two types of lap joints: single lap joint (SLJ) and double lap strap joint (DLSJ) were fabricated. The joints were fabricated using Al 5083 as adherends. The adherends were treated with phosphoric acid anodization (PAA) before joining. A comparison of the strength properties was made after tensile testing of the adhesive specimens and lap joints. In the case of adhesive samples, an increase in mechanical properties was observed at lower concentrations. A maximum increase of 9.5% in the tensile strength and 128% in toughness characteristics was observed with the addition of 0.25 wt% RGO. A maximum improvement of 24% for SLJ and 25% for DLSJ was observed at the same filler percentage. Chemical analysis was conducted using Fourier-Transform Infrared Spectroscopy (FTIR), while dispersion analysis was carried out using Ultraviolet–Visible Spectroscopy (UV-VIS-Nir). Digital and Scanning Electron Microscopy (SEM) techniques were utilised in close examination of the fracture surface at high magnification. A finite element analysis based on cohesive zone modelling (CZM) was performed to predict the failure load characteristics of lap joints. Finally, a comparison of strength and fracture behaviour of RGO with GNPs and MWCNTs was critically discused.

EFFECT OF VOLTAGE ON THE THICKNESS OF OXIDE LAYER AT ALUMINUM ALLOYS FOR STRUCTURAL BONDING USING PHOSPHORIC SULFURIC ACID ANODIZING (PSA) PROCESS

The aerospace industry mostly uses the aluminum alloys 2xxx and 7xxx series for their fuselage construction, and some of them are assembled using structural bonding because it is strong, easy during the fabrication process, resistant to corrosion, and non-toxic. The anodization process is a proven surface treatment method for structural bonding. Phosphoric Sulfuric Acid Anodizing (PSA) is an eco-friendly alternative as a chromate-free solvent technology for the anodizing process that is applied for structural bonding. The thickness of the oxide layer caused by the voltage given in this process was evaluated in terms of corrosion resistance using the oxide layer's thickness as the main factor. The PSA process of AA2024 T3 clad was carried out at a constant concentration of 125 g/L of phosphoric acid, 80 g/L of sulfuric acid, 27 A, and a temperature of 26 to 28 OC for 23 minutes with various voltages. The voltage was varied at 16, 18, and 20 VDC. The optimum condition for the voltage applied was 18 VDC, which resulted in an oxide layer thickness of 2.76 µm.

Development of Photocatalytically Active Anodized Layers by a Modified Phosphoric Acid Anodizing Process for Air Purification

One of the key urban air quality issues is pollution by nitrogen oxides (NOx). To reduce NOx, facade cladding could be provided with photocatalytic properties by incorporating titanium dioxide nanoparticles. For this purpose, a modified phosphoric acid anodizing process (MPAA) was developed for the facade alloy EN AW-5005, in which highly ordered anodized structures with a low degree of arborization and tortuosity were produced. Pore widths between 70 nm and 150 nm and layer thicknesses of about 2–3 μm were obtained. The subsequent impregnation was carried out by dip coating from water-based systems. Depending on the dip-coating parameters and the suspension used, the pores can be filled up to 60% with the TiO2 nanoparticles. Photocatalytic tests according to ISO 22197-1 certify a high photocatalytic activity was obtained with rPCE values > 8 and with rPCE > 2, achieving “photocatalytically active for air purification”. Tests on the corrosion resistance of the anodized coatings with a commercially available aluminum and facade cleaner confirm a protective effect of the anodized coatings when compared with nonanodized aluminum material, as well as with compacted anodized layers.

Effect of anodizing surface morphology on the adhesion performance of 6061 aluminum alloy

An experimental investigation on the phosphoric acid anodizing process of 6061 aluminum alloy has been carried out to enhance the adhesive bonding strength of 6061 aluminum alloy and the carbon fiber reinforced thermo-plastic. The phosphoric acid anodizing parameters of 6061 aluminum alloy were optimized by an orthogonal experiment design, and substrates with different surface morphologies were obtained. The surface free energies, surface roughness, and joint failure morphologies of samples with specific surface morphology were examined and analyzed to comprehensively evaluate the effect of surface morphology on the bonding performance of joints in high-temperature applications. The results indicate that under appropriate conditions, phosphoric acid anodization can change the fracture mode of the joint between the 6061 aluminum alloy and thermoplastic polyetheretherketone adhesive, as well as improve the performance of the joint. The appropriate number of circular structure pits on the surface of the aluminum alloy is key to improving the shear strength of the joint.

Effect of surface morphology characteristic parameters on the shear strength of aluminum bonded joints

To understand the effect of surface morphology on the shear strength and failure mode of single-lap joints with micron-thickness bondline, sandblasting and phosphoric acid anodizing (PAA) methods were used to treat the surface of the 2A12 substrates. Compared with the original milling surface, the Ra values of the sandblasting surface increased by 7–10 times, but the peak count number (Rpc) reduces by 20%–50%, which made the sandblasting surface “smoother” in micron- or nano-scale. The PAA method has slight effect on the Ra, Rz, and Rpc values in micron-scale, while it can generate a porous anodic film and change the morphology in nano-scale. For the sandblasted surface, the shear strength first slightly increases with the increase of the Ra value but then decreases due to the decrease of Rpc. For the micron-level bondline, the surfaces treated by the PAA method show much higher shear strength and a greater degree of cohesive failure than those only by the physical methods.

Persistent reduction of boiling incipience of ethanol on biphilic porous textured surfaces

Boiling of highly wetting fluids is of great interest to thermal management of high-powered electronic devices, enhancement of which conventionally relies on functional modifications of surface shape and structure so as to promote bubble generation and growth. In this paper we attempt to combine the approach of porous texturing with a novel technique of surface wettability engineering to enhance saturated pool boiling of ethanol. Thin layers of microporous and nanoporous surface topographies were chemically deposited on an aluminum substrate by anodization in phosphoric acid and sulfuric acid, respectively. Boiling on the textured surfaces recorded over-twofold increases in terms of the heat transfer coefficient compared with that on a plain smooth surface, which can be attributed to a proliferation of active nucleation sites. The boiling incipience point on both porous surfaces, however, exhibited an interesting dependence on the initial wetting state of the surface. With the application of amphiphobic coatings of fluoropolymer modified with halloysite nanotubes, we managed to engender a biphilic (i.e., spatially alternating hydrophobicity and hydrophilicity) pattern on the porous-textured surfaces. The repeat control experiments on the hybrid surfaces showed an equally efficient mode of nucleate boiling, whose inception, by contrast, seemed to occur at consistently low superheats. The remarkable reduction (by more than 80%) of the minimum superheat at the boiling onset hints at an alternative nanobubble-related mechanism for heterogeneous bubble nucleation, which is notably less affected by incondensable gas, to the classic vapor-trapping-cavity model.

Properties and characterization of novel 3D jute reinforced natural fibre aluminium laminates

Fibre metal laminates (FML) are being used in automotive, aerospace and naval applications due to their light weight and superior performance. The FMLs are made by sandwiching composite with metal. The environmental concerns due to non-biodegradability of such structures, lead to the development of FML containing natural fibre composites. Natural fibres composite, despite having good damping properties have overall poor mechanical properties. However, this aspect can be improved by weaving the fibres in 3 D pattern. In literature, FML made using 3 D woven jute composites is never reported. Furthermore, no literature is found on adhesion of natural fibre composite-metal bonding. In this paper, development of novel 3 D Jute Reinforced natural fibre Aluminium Laminates (JuRALs) is reported. Furthermore, the effect of 3 D weaving pattern and metal-composite bonding on mechanical properties and failure mechanism of the developed samples is also discussed in detail. The four-layered 3 D woven Jute fabric reinforcement was made using four interlocking patterns. The composites and JuRALs were fabricated using epoxy resin by vacuum infusion technique. The surface of aluminium was treated using phosphoric acid anodizing. Tensile, flexural and T-peel tests were performed according to ASTM testing method using Z100 All-round, Zwick Roell. The results showed that out of four types of used reinforcements, the through-thickness composites had better tensile properties while layer-to-layer composite had better flexural properties. The tensile and flexural properties of JuRALs made with through-thickness interlock reinforcement were better as compared to layer-to-layer interlock reinforcement. The T-peel results depicted that the constituent materials influenced the metal-composite adhesion properties, rather the type of 3 D structure.

Durability of Metal-Composite Friction Spot Joints under Environmental Conditions.

The current paper investigates the durability of the single-lap shear aluminum-composite friction spot joints and their behavior under harsh accelerated aging as well as natural weathering conditions. Four aluminum surface pre-treatments were selected to be performed on the joints based on previous investigations; these were sandblasting (SB), conversion coating (CC), phosphoric acid anodizing (PAA), and PAA with a subsequent application of primer (PAA-P). Most of the pre-treated specimens retained approximately 90% of their initial as-joined strength after accelerated aging experiments. In the case of the PAA pre-treatment, the joint showed a lower retained strength of about 60%. This was explained based on the penetration of humidity into the fine pores of the PAA pre-treated aluminum, reducing the adhesion between the aluminum and composite. Moreover, friction spot joints produced with three selected surface pre-treatments were held under outside natural weathering conditions for one year. PAA-P surface pre-treated specimens demonstrated the best performance with a retained strength of more than 80% after one year. It is believed that tight adhesion and chemical bonding reduced the penetration of humidity at the interface between the joining parts.

Surface Reconstruction, Hydration, and Adhesion of Epoxy to the (0001) Surface of α-Berlinite: Insights from Density Functional Theory Calculations

Phosphoric acid anodization (PAA) is a candidate for replacement of toxic chromates during the surface treatment of aluminum prior to gluing in the aerospace industry. During PAA, a layer of AlPO4 ...

Effects of surface pre-treatment and adhesive quantity on interface characteristics of fiber metal laminates

ABSTRACT Fiber metal laminates (FMLs) are hybrid materials consisting of metals and fiber-reinforced composite materials. The characteristics of interfaces between metal layers and layers of composites directly determine the damage tolerance and impact resistance of FMLs. In this study, the effects of surface pre-treatment and adhesive quantity on the interface of FMLs were investigated. Aluminum substrates were treated with sandpaper and anodizing. The treated surface structure and joint shear strength were evaluated to analyze the bonding interface quality. The results show that the surface roughness, structure and thickness of the anodized films affect the interface characteristics and adhesion strength. A porous oxide layer was formed on the substrate surface after anodization, resulting in a better wetting surface than that of sanded. Moreover, statistical analysis of the surface structures reveals that the shear strength of phosphoric acid anodizing treatment was higher than other anodizing. With the increase in adhesive layers, the lap shear strength was markedly improved at the beginning but slowly increased thereafter. From the results, the surface pre-treatment and adhesive quantity could be optimized to improve the manufacturing process of FMLs.

Characterization and properties of AA6061-based fiber metal laminates with different aluminum-surface pretreatments

In this study, an Al/CFRP/Al laminates was prepared with three types of aluminum alloy AA6061 surface treatments (sanding, anodizing, and surface modification) to improve the metal–composite interface (MCI) strengths. The results showed that the shear strengths of Al/CFRP/Al laminates modified by silane coupling agent and pretreated by phosphoric acid anodizing were similar, approximately 50 MPa, which were significantly higher than those subjected to sandpaper-sanding pretreatment (38 MPa). Results of scanning electron microscopy (SEM) revealed that the nanoscale porous anodized film produced on the AA6061 surface after anodizing pretreatment enhanced the wettability of CFRP on AA6061 sheets, leading to strong interfacial bonding. XPS analysis showed that a new chemical bond, AlOEP, appeared at the interface between CFRP and anodized AA6061, which clearly indicated that the anodized layer could enhance the mechanical anchoring effect and promote its chemical reaction. And the chemical bonds of AlOSi and SiC were found at the interface between CFRP and silane-modified AA6061, thereby proving the existence of a silane flexible layer, which enabled the adjustment of the thermal expansion coefficient mismatch between AA6061 and CFRP and the improvement in the stability of the mechanical properties of Al/CFRP/Al laminates.

The effect of chemical additives in phosphoric acid anodization of aluminum-tantalum thin films

Biosensor development has relied on the process of anodization of sputtered aluminum‑tantalum thin films to develop specific optical properties for interference color generation. The anodization of thin sputtered films of aluminum (140 nm) on tantalum (230 nm) on silicon was completed in 0.4 M phosphoric acid under potentiostatic conditions (4 V) and with various additives: 0.1 M and 0.4 M citric acid, 3% (v/v) and 10% (v/v) of a commercial anodizing solution consisting of glycerol and glycolic acid, and 0.1 M and 0.4 M oxalic acid. The microstructural and optical properties of these films were analyzed using scanning electron microscopy, X-ray diffraction, and ellipsometry. The interference colors produced by the anodic aluminum and tantalum oxides on top of the tantalum metal layer were also observed. The addition of 0.1 M citric acid, 3% (v/v) glycerol and glycolic acid-based solution, and 0.1 or 0.4 M oxalic acid all produced changes to the porous microstructure of the anodic alumina, including lower roughness and more homogeneous surfaces by inhibition of the dissolution from phosphoric acid. Oxalic acid acted as the strongest inhibitor and significantly reduced surface roughness and pore size, increased the composite refractive index of the anodized film, and significantly changed the interference colors compared to films where no additive was used.

Surface Treatment for Improving Durability of Aluminum-Lithium Adhesive-Bonded Joints under Hot-Humid Exposure

The performance of adhesive-bonded joints, which are being increasingly used in the aerospace and automotive industries, under hot-humid conditions remains largely unknown. The effect of surface treatments on the strength durability of aluminum-lithium (Al-Li) alloy adhesive-bonded joints under hot-humid exposure was investigated. Varied surface characteristics were achieved by different mechanical and chemical treatments; combined mechanical and phosphoric acid anodization (PAA) treatments were also used. The adhesive-bonded joints were then exposed to a hot-humid environment. The surface morphology, strength degradation, failure modes, and corrosion resistance of the substrates were analyzed. The results indicated that the combined PAA/mechanical method improved the joint durability under hot-humid exposure. The treated surface, with a roughness of 2.85 μm, exhibited the best durability, losing only 6% of strength after exposure; the failure mode remained cohesive-failure dominant. The durability enhancement was attributed to the porous and moderate rough surface characteristics, which protected the substrate from corrosion and decreased the rate of moisture diffusion from the bonding interface, thereby reducing the degradation of the bonding interface and improving the durability of the joint.

Effect of combined surface treatment on the adhesion performance of aluminium-lithium alloy

Herein we investigated the effect of various surface treatments, especially the combined surface treatment of grit-blasting and phosphoric acid anodization (PAA), on the surface characteristics and the adhesion performance of aluminium-lithium alloy sheets. For the combined surface treatment, rough surfaces were firstly created by grit-blasting to increase the surface area available for anodization. Next, porous structures were produced on the grit-blasted surfaces by PAA. The surface characteristics, surface wettability, fracture morphology, and shear strengths of samples subjected to different surface treatments were compared and analyzed. The effect of surface roughness on the bonding strength of aluminium-lithium alloys subjected to combined treatments was also investigated. The experimental results showed that combined treatment provided the best wettability and single-lap joint performances, with the highest surface free energy of 81.4 mJ/m2 and shear strength of 40.8 MPa.

Nanoparticle-based impregnation of chromate-free anodizing layers for corrosion protection and adhesive bonding

The present work suggests a new approach of chromate-free surface pretreatment of aluminum alloy AA 1050 by using a modified phosphoric acid anodizing process, followed by an impregnation with a commercial SiO2-nanoparticle dispersion (Levasil® 300/30%) by dip-coating technique. The nanoparticles constitute an additional barrier layer against corrosion without closing the pores completely. The open porous oxide layer is a suitable promoter of adhesive bonding. The influence of withdrawing speed, the dipping time, solid content, temperature and pH-value in respect to the filling height in the pores of the anodized oxide layer were investigated. Surface morphology of the impregnated anodic oxide layers as well as their cross-section microstructure were investigated by scanning electron microscopy (SEM). Corrosion properties were investigated by electrochemical impedance spectroscopy (EIS) and adhesion was evaluated by single lap shear tests.

Tuning the optical properties of nanoporous anodic alumina photonic crystals by control of allowed voltage range via mixed acid concentration

This study investigates the tunable fabrication of photonic crystals (PCs) based on nanoporous anodic alumina (NAA) templates through modification of nanopore diameter, affecting the PCs optical response. This was realized by controlling phosphoric acid concentration (CPh) and anodization current density. This approach along with chemical etching offers the opportunity to adjust optical band gap in a wide range of wavelengths (from about 400 to 1100 nm). To this end, the effect of CPh on current density and threshold voltage was investigated. To analyze formation mechanism of resulting multilayers and optimize their optical characteristics, the potential ratio, span, cycles and charge density were examined, thereby providing a band gap as narrow as 6 nm. The sensing analysis revealed that the modified multilayer shows enhanced sensitivity to the changes of effective media inside the nanopores. These findings provide insights into the development of both optical sensors and optoelectronic nanodevices based on the NAA-based PCs.