Influence of oxidation heat on hard anodic film of aluminum alloy

The special experimental device and sulfuric acid electrolyte were adopted to study the influence of anodic oxidation heat on hard anodic film for 2024 aluminum alloy. Compared with the oxidation heat transferred to the electrolyte through anodic film, the heat transferred to the coolant through aluminum substrate is more beneficial to the growth of anodic film. The film forming speed, film thickness, density and hardness are significantly increased as the degree of undercooling of the coolant increases. The degree of undercooling of the coolant, which is necessary for the growth of anodic film, is related to the degree of undercooling of the electrolyte, thickness of aluminum substrate, thickness of anodic film, natural parameters of bubble covering and current density. The microstructure and performance of the oxidation film could be controlled by the temperature of the coolant.

Effects of boric acid on microstructure and corrosion resistance of boric/sulfuric acid anodic film on 7050 aluminum alloy

The microstructure and corrosion resistance of different boric/sulfuric acid anodic（BSAA） films on 7050 aluminum alloy were studied by atomic force microscopy（AFM）,electrochemical impedance spectroscopy（EIS） and scanning Kelvin probe（SKP）.The results show that boric acid does not change the structure of barrier layer of anodic film,but will significantly affect the structure of porous layer,consequently affect the corrosion resistance of anodic film.As the content of boric acid in electrolyte increases from 0 to 8 g/L,the resistance of porous layer（Rp） of BSAA film increases,the capacitance of porous layer（CPEp） decreases,the surface potential moves positively,the pore size lessens,and the corrosion resistance improves.However,the Rp,CPEp and surface potential will change towards opposite direction when the content of boric acid is over 8 g/L.

Reaction behavior between the oxide film of LY12 aluminum alloy and the flux

In this paper, the brazing mechanism of LY12 aluminum alloy at middle range temperature was presented. The CsF-AlF_3 non-corrosive flux was utilized to remove the complex oxide film on the surface of LY12 aluminum alloy. The results revealed that the oxide film was removed by the improved CsF-AlF_3 flux accompanied with the occurrence of reaction as well as dissolution and the compounds CsF played an important role to remove the oxide film. Actually, the high activity of flux, say, the ability to remove the oxide film, was due to the presence of the compounds, such as NH_4F,NH_4AlF_4 and composite molten salt. The production of HF was the key issue to accelerate the reaction and enhance to eliminate the oxide film by dissolution. It was found that the rare earth element La at small percentage was not enriched at the interface. Moreover, the rare earth fluoride enhanced the dissolution behavior.

Correspondence between Susceptibility to SCC of 7050 Aluminum Alloy and Passive Film-induced Stress at Various pH Values

The passive film-induced stress and the susceptibility to SCC of 7050 aluminum alloy in 3.5%sodium chloride solution at various pH values were investigated by slow strain rate testing（SSRT） and flowing stress differential method.The results showed that the passive film-induced stress and the susceptibility to SCC decreased with increasing pH values when pH≤7,while they increased with increasing pH values when pH7.However,the corrosion type was interpreted as exfoliation corrosion when pH=l and 14,and there was no film formed on the surface of the specimens.The whole variation plots of film-induced stress and the SCC susceptibility with pH values were both presented as a valley shape.The symbol and amount of the film-induced stress were related to the compositions of the passive film,which were analyzed using X-ray photoelectron spectroscopy（XPS）.

Effects of acetic acid on microstructure and electrochemical properties of nano cerium oxide films coated on AA7020-T6 aluminum alloy

Nano cerium oxide films were applied on AA7020-T6 aluminum alloy and the effects of acetic acid concentration on the microstructure and electrochemical properties of the coated samples were investigated by using scanning electron microscopy （SEM）, X-ray diffraction （XRD）, and potentiodynamic polarization methods. It has been found that by increasing the acetic acid/CeCl3·7H2O molar ratio, high uniform and crack-free films with well-developed grains were obtained and grain sizes of the films decreased. Elimination of cracks and decreasing grain size of the nano cerium oxide films caused corrosion resistance to increase.

Preparation of anodic films on 2024 aluminum alloy in boric acid-containing mixed electrolyte

The anodizing oxidation process on 2024 aluminum alloy was researched in the mixed electrolyte with the composition of 30 g/L boric acid, 2 g/L sulfosalicylic acid and 8 g/L phosphate. The results reveal that the pre-treatment and the composition of the mixed electrolyte have influence on the properties of the films and the anodizing oxidation process. Under the condition of controlled potential, the anodizing oxidation current—time response curve displays "saddle" shape. First, the current density reaches a peak value of 8-20 A/dm2 and then decreases rapidly, finally maintains at 1-2 A/dm2. The film prepared in the mixed electrolyte is of porous-type with 20 nm in pore size and 500 μm-2 in porosity. Compared with the conventional anodic film obtained in sulfuric acid, the pore wall of the porous layer prepared in this work is not continuous, which seems to be deposited by small spherical grains. This porous structure of the anodic film may result from the characteristics of the mixed electrolyte and the special anodizing oxidation process. The surface analysis displays that the anodic film is amorphous and composed of O, Al, C, P, S, Si and no copper element is detected.

Evolution of Surface Oxide Film of Typical Aluminum Alloy During Medium-Temperature Brazing Process

The evolution of the surface oxide film along the depth direction of typical aluminum alloy under mediumtemperature brazing was investigated by means of X-ray photoelectron spectroscopy(XPS). For the alloy with Mg content below 2.0wt%, whether under cold rolling condition or during medium-temperature brazing process, the enrichment of Mg element on the surface was not detected and the oxide film was pure Al2O3. However, the oxide film grew obviously during medium-temperature brazing process, and the thickness was about 80 nm. For the alloy with Mg content above 2.0wt%, under cold rolling condition, the original surface oxide film was pure Al2O3. However, the Mg element was significantly enriched on the outermost surface during medium-temperature brazing process, and MgO-based oxide film mixed with small amount of MgAl2O4 was formed with a thickness of about 130 nm. The alloying elements of Mn and Si were not enriched on the surface neither under cold rolling condition nor during mediumtemperature brazing process for all the selected aluminum alloy, and the surface oxide film was similar to that of pure aluminum, which was almost entire Al2O3.

Effect of deposition parameters on mechanical properties of TiN films coated on 2A12 aluminum alloys by arc ion plating (AIP)

TiN films were deposited on 2A12 aluminum alloy by arc ion plating (AIP). The Vickers hardness of the films deposited at different bias voltages and different nitrogen gas pressures, and that of the substrate were measured. The surface roughness of the TiN films diposited at –30 V and –80 V respectively and at different nitrogen gas pressure was measured also. The mass loss of TiN films deposited at 0 V, –30 V and –80 V respectively were analyzed in dry sand rubber wheel abrasive wear tests and wet ones in comparison with uncoated Al alloy and austenitic stainless steel (AISI 316L). It is revealed that the highest hardness of the TiN film is obtained at a bias voltage of –30 V and a N2 gas pressure of 0.5 Pa. The surface roughness of the film is larger at –80 V than that at –30 V and reduces as the increase of the N2 gas pressure. The mass loss of TiN-film coated 2A12 aluminum alloy is remarkably less than that of uncoated Al alloy and also that of AISI 316L, which indicates that the abrasive wear rate is greatly reduced by the application of TiN coating. TiN coating deposited by arc ion plating (AIP) technique on aluminum alloy can be a potential coating for machine parts requiring preciseness and lightness.

Evolution of insoluble eutectic Si particles in anodic oxidation films during adipic–sulfuric acid anodizing processes of ZL114A aluminum alloys

The effects of insoluble eutectic Si particles on the growth of anodic oxide films on ZL114A aluminum alloy substrates were in- vestigated by optical microscopy （OM） and scanning electron microscopy （SEM）. The anodic oxidation was performed at 25℃ and a con- stant voltage of 15 V in a solution containing 50 g/L sulfuric acid and 10 g/L adipic acid. The thickness of the formed anodic oxidation film was approximately 7.13 μm. The interpore distance and the diameters of the major pores in the porous layer of the film were within the ap- proximate ranges of 10~20 nm and 5-10 nm, respectively. Insoluble eutectic Si particles strongly influenced the morphology of the anodic oxidation films. The anodic oxidation films exhibited minimal defects and a uniform thickness on the ZL114A substrates; in contrast, when the front of the oxide oxidation films encountered eutectic Si particles, defects such as pits and non-uniform thickness were observed, and pits were observed in the films.

Corrosion Mechanism of 5083 Aluminum Alloy in Seawater Containing Phosphate

As a material with good corrosion resistance,5083 aluminum alloy has a great application prospect in marine environment.In this work,the corrosion characteristics of 5083 aluminum alloy in seawater containing phosphate were investigated with Potentiodynamic Polarization,Electrochemical Impedance Spectroscopy (EIS),Scanning Electron Microscope (SEM),Energy Dispersive Spectroscopy Analysis (EDSA),X-ray Photoelectron Spectroscopy (XPS) and Laser Confocal Microscope.The results indicated that the effects of phosphate in seawater were two-fold.Firstly,phosphate slightly accelerated the corrosion of 5083 in seawater in the early stage of corrosion.HPO_4~(2-)competed with OH~-in the adsorption process on the alloy surface,which weakened the contact between OH~-and Al~(3+)near the interface of the alloy,and inhibited the formation as well as the self-repair of the passive film,thus accelerating the activation dissolution process.Compared with the natural seawater,the charge transfer resistance of 5083 in the seawater containing phosphate decreased faster during the early stage of corrosion,and the corrosion current density i_(corr) was higher in seawater containing phosphate.On the other hand,the addition of phosphate would not affect the cluster distribution of the second phase of 5083 in seawater,but it changed the composition of the corrosion product layer and had an obvious inhibitory effect on the local corrosion of 5083 in seawater.After 16-day exposure,shallower and more sparsely distributed pits could be observed on the derusted surface of 5083 in the seawater containing phosphate,and the pitting coefficient in the seawater containing phosphate was significantly lower than that in natural seawater.The reduction of pitting tendency could be realized mainly through two ways.First,the HPO_4~(2-)adsorbed on the surface of the passive film in the early stage of corrosion and repeled the corrosive anions such as Cl~-.Second,phosphate participated in the construction of the Ca HPO_4 precipitation film,which acted as a barrier and protection.

Anodizing parameters for superheated slurry cast 7075 aluminum alloys

The anodizing parameters of voltage, current density, temperature, and electrolyte choice were assessed to find an appropriate combination for the superheated slurry cast 7075 Al alloy substrate.The alloy was anodized in sulfuric acid electrolyte or alternatively in sulfuric acid mixed with boric acid or citric acid. The voltages applied were in the range of 15-30 V. Anodizing current densities tested were 2 and 3 A/dm^2,while temperatures tested were 5 and 15 ℃. Thickness, surface morphology, hardness,and corrosion resistance of the oxide film were then evaluated.It was found that 25 V,2 A/dm^2 and 5 ℃ were suitable for this alloy when anodized in sulfuric acid. The oxide film was smooth with uniform thickness, low porosity, high hardness,and had the highest corrosion resistance at these parameters. However, discontinuous oxide films were observed from samples anodized at higher temperature of 15 ℃.Alternative electrolytes considered were sulfuric acid mixed with boric acid or citric acid. The results showed that electrolytes with boric acid or citric acid increased thickness, hardness, corrosion resistance and quality of the oxide films.However, these oxide films were inferior to those obtained with sulfuric acid electrolyte at lower temperature(25 V, 2 A/dm^2 and5 ℃).

Effect of intermetallic phases on the anodic oxidation and corrosion of 5A06 aluminum alloy

Intermetallic phases were found to influence the anodic oxidation and corrosion behavior of 5A06 aluminum alloy. Scattered in- termetallic particles were examined by scanning electron microscopy （SEM） and energy dispersive spectroscopy （EDS） after pretreatment. The anodic film was investigated by transmission electron microscopy （TEM）, and its corrosion resistance was analyzed by electrochemical impedance spectroscopy （EIS） and Tafel polarization in NaC1 solution. The results show that the size of A1-Fe-Mg-Mn particles gradually decreases with the iron content. During anodizing, these intermetallic particles are gradually dissolved, leading to the complex porosity in the anodic film beneath the particles. After anodizing, the residual particles are mainly silicon-containing phases, which are embedded in the an- odic film. Electrochemical measurements indicate that the porous anodic film layer is easily penetrated, and the barrier plays a dominant role in the overall protection. Meanwhile, self-healing behavior is observed during the long immersion time.

Numerical Simulation on Nugget Formation and Evolution in Spot Welding of Aluminum Alloy

With the squeeze of electrode tips, the oxide film on aluminum (Al) alloy surface is broken and numbers of micro-gaps are formed randomly. The micro-gaps act as conducting spots at the beginning of welding, so the contact resistance is extremely high and unstable in spot welding of Al alloy. In this paper, a new contact resistance model is adopted to simulate the nugget forming process. This model describes the random distribution characteristic of conducting spots. The simulation results indicate that, within the first 5 ms of welding current (AC, 50 Hz), the temperature distribution at the workpieces interface is seriously irregular. In addition, the nugget does not nucleate from the weld center and grow continuously, however, it nucleates randomly from several points almost instantaneously and then merges into an entity quickly. Experimental results agreed with the numerical simulation.

Effects of current density on the corrosion behaviour of anodized aluminum alloy in FeCl_3 solution

In the present study, 2024 aluminum alloy specimen was anodized in acetic acid and oxalic acid e- lectrolytes. Effects of the current density on the microstructure and corrosion resistance of anodic oxide film have been investigated. The steady voltage increases from 11 V to 71 V with the current density increase from 0. 5 A/din2 to 2. 5 A/din2. The SEM reveals that there are pits, cavities and irregular pores in the anodic film, and their size and morphologies change with the current density. The corrosion resistance of the film was evalua- ted by potentiodynamic polarization and electrochemical impedance in 0.1 mol/L FeC13 solution at room temper- ature. The results show that corrosion resistance of the anodic oxide film changes with the current density, and the anodic fihn formed at the current density of 1.0 A/dm2 has the best corrosion resistance. These observations indicate that anodic film formed at J -- 1.0 A/dm2can serve as a support material for the Cu micrometallic pat-

Study of corrosion protection of the composite films on A356 aluminum alloy

Composite films were fabricated on A356 aluminum alloy by combined anodizing and rare earth deposition. The corrosion protection effect and corrosion behavior of the composite films in 3.5% NaCl solution were studied by electrochemical impedance spectroscopy （EIS）. SEM observation indicated that the rare earth Ce film completely sealed the porous structure of the anodic film, and the composite films composed of anodic film and Ce film were compact and integrated. According to the characteristics of EIS, the EIS plots of the compos- ite films at different immersion times were simulated using the equivalent circuits of Rsol（QceRce）（QaRa）, Rsol（QceRce）（QpRp）（QbRb） and Rsoj（QpRp）（QbRb） models, respectively. The test results showed that the Ce film at the outer layer of the composite films had good protection effect at the initial stage of the immersion corrosion. It effectively helped the anodic film at the inner layer to prevent chloride irons from penetrating the aluminum alloy matrix. After 18 days, the Ce film lost its anticorrosive property, and the anodic film took the leading role of the corrosion protection. When the corrosion time was up to 42 days, the aluminum matrix was not corroded yet. Thus, the higher protection degree of the composite films for A356 aluminum alloy was attributed to the synergism effects of anodic film and rare earth Ce film.

Nickel-free sealing technology for anodic oxidation film of aluminum alloy at room temperature

Different additives were added into the potassium fluorozirconate solution to prepare different nickelfree sealing reagents,with which the anodic oxidation film of aluminum alloy was sealed at room temperature.The phosphor chromic acid weight loss method was used to evaluate the sealing effects.Using electron scanning microscopy(SEM),the surface and cross-sectional micromorphologies of the anodic oxidation films sealed by different fluorozirconate sealants were observed.The position and state of zirconium element distribution in the film hole were investigated by the further quantitative and distribution analysis of Zr element.This study provides an experimental evidence for the theoretical studies of fluorozirconate-sealed anodic oxidation films.It is shown that the fluorozirconate has good sealing effects and has a wide prospect for sealing the aluminum alloy samples.Its products were highly corrosion resistant,and were filled in the openings of the micropores in the oxide film.

Influence of silane on corrosion resistance of magnesium alloy AZ31 with thermally sprayed aluminum coatings

Aluminum coatings on Mg alloy AZ31 were fabricated using the thermal spraying technique, and then sealed with silane.The surface morphology and chemical groups were discerned using scanning electron microscopy and examined using Fourier transformation infrared spectroscopy, respectively.The salt fog tests and the potentiodynamic electrochemical technique were applied to evaluate the influence of silane on corrosion of the AZ31 alloy with aluminum coatings.The results showed that the corrosion resistance of the aluminum-coated AZ31 alloy was superior to that of the substrate.The aluminum coating sealed with various silane layers led to a further increase in the corrosion resistance of the alloy.Double silane layers were more corrosion-resistant than the single one.Also, it was no longer significant for more than two silane layers to improve the corrosion resistance.It implied that the optimum choice for silane treatment on the aluminum coatings was two layers.

Effect of Initial Oxide Film on the Formation and Performance of Plasma Electrolytic Oxidation Coating on 7075 Aluminum Alloy

In the early stage of plasma electrolytic oxidation(PEO),the quick formation of the initial oxide film on the surface of the aluminum substrate is necessary for the subsequent discharge spark process.Furthermore,the compactness of the initial oxide film greatly affects the quality of the PEO coating,but the related mechanisms are not investigated in detail.In this paper,the status of the initial oxide film was adjusted by adding the(NaPO)into the based electrolyte,and then the effect of initial oxide film on the formation of the PEO coating was compared.Microstructure and chemical composition were analyzed by scanning electron microscope,transmission electron microscopy and X-ray photoelectron spectrometer.The compactness of the initial oxide film was characterized by Mott-Schottky plots.The corrosion resistance was measured by electrochemical impedance spectroscopy.The results show that the addition of(NaPO)can promote the co-deposition of phosphide compound into the initial oxide film and improve the film compactness,which is beneficial for the more uniform spark discharge in the later stage.As a result,the addition of(NaPO)is helpful to obtain PEO coating with better performance.

Effect of Alloying Elements on the Quality of Hard Anodic Oxidation Film in Aluminum Alloy 6061

the effect of different Mg/Si and Mn content on uniformity and consistence of anodic films of 6061 aluminum alloy was investigated by using hardness test,coating thickness test, optical microscopy (OM),scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results show that when Mg/Si is in the vicinity of 1.73 and Mn content is 0.14%, the uniformity of the anodic film is the best while the consistence of the anodic film is the best when Mg/Si is 1.88 and Mn content is 0.14%. Superfluous silicon and magnesium have a bad function on the uniformity of anodic films of 6061 aluminum alloy because of secondary phases but magnesium in the base material can be beneficial for the consistence of the anodic film due to formation of a protective, impermeable layer of MgO below the anodic film while plentiful excess silicon result in single Si and w(Cu4Mg5Si4Alx) to gather in the grain boundary, which makes rarefactions and discontinuity present. The uniformity and consistence of anodic films are improved by Mn content rising, which is caused by the decrease of needle-like Fe-rich and Mg2Si phases and the increase of bone-like Fe-rich phases.

Effect of depressurizing speed on mold filling behavior and entrainment of oxide film in vacuum suction casting of A356 alloy

The effect of depressurizing speed on mold filling behavior and entrainment of oxide film of A356 alloy was studied. Themold filling behavior and velocity fields were recorded by water simulation with particle image velocimetry. The results show thatthe gate velocity first increased dramatically, then changed with the depressurizing speed: the gate velocity increased slowly atrelatively high depressurizing speed; at reasonable depressurizing speed, the gate velocity kept unchanged; while at lowerdepressurizing speed, the gate velocity decreased firstly and then kept unchanged. High gate velocity results in melt falling backunder gravity at higher speed. The falling velocity is the main factor of oxide film entrainment in vacuum suction casting. The designcriterion of depressurizing rate was deduced, and the A356 alloy castings were poured to test the formula. The four-point bend testand Weibull probability plots were applied to assessing the fracture mechanisms of the as-cast A356 alloy. The results illuminate amethod on designing suitable depressurizing speed for mold filling in vacuum suction casting.