STUDY THE EFFECT OF COATING USING NANOPARTICLES ON THE CORROSION OF ALUMINUM ALLOY IN DIFFERENT SOLUTIONS

-3 and 8.183×10 -3 ) have been obtained with (1 , 3 and 5 wt% TiO 2 ) respectively. The results have been confirmed by using a constant dip-coating speed of 200 mm/min, and the results of the corrosion rate for 200,150 and 100 mm/min have been 7.131×10 -4 , 7.984×10 -4 and 8.293×10 -4 respectively. The morphology of coating film which characterized by SEM, have shown that the TiO 2 NPs spread and was covered by epoxy very well. The AFM test used to study the surface average roughness of coating film where the Ra for sample with epoxy coating is24.4 nm and for sample with (epoxy _1%wt TiO 2 ) is 1.508 nm.


ISSN: 2320-5407
Int. J. Adv. Res. 9(01), 622-633 623 oxide layer formation rises the corrosion resistance of the alloy, this layer is easily eroded. This erosion can be credited to defects in the oxide layers. Chloride ions and atmosphere areexposed suffer attacks, leading to more deterioration [4].There are numerous corrosion resistant systems obtainable on the market today, coatings areone of these systems have been completely positive in inhibiting corrosion, there has continuously been a question mark on the dependability of some critical properties of the coatings, such as resistance to water permeation, precise control over surface morphology and uniformity and adhesion to the substrate, For over a decade researchers andscientists in the coatings and corrosion fields have turned to nanotechnology in a constant effort to be more precise in explanation the corrosion natural phenomena at the nano level (10 −9 m). The nanotechnology application has produced many invaluable coatings and materials to minimize corrosion degradation [5].
Corrosionprevention of metal by nanocoating, it is manufacturing process begins with the selection of an appropriate substrate. The substrate can come from the typical metallic elements (e.g., Al, Ti, Cu or Au) and alloys (e.g., Ni-Fe, Ti-Al or Pb -Sn) for industrial applications or from ceramics (e.g., AlN, GaN, TiN, SiO 2 , TiO 2 , Al 2 O 3 , ZrO 2 , etc.) and semiconductors (e.g., Si and quartz) for micro electro mechanical (MEMS) devices such as electronic actuators, filter elements, catalytic membranes, micro pumps and drug delivery systems [6].
A. S.Hamdy [7]discussed vanadate compounds friendly eco-environmentally surface treatments as replacements to the toxic chromates for Al alloys corrosionprotection. Cleaning,etching by (KOH)process includes, and then treatment by vanadiasol-gelwas prepared. The corrosionresistance of AA6061 T6 in 3.5% NaCl solution has been measuredbefore vanadia treatment using DC polarization techniques and AC impedance spectroscopy.Scanning Electron microscopic,(EDS), (XPS) and (AFM)was performed to Surface examination. The resultes show that theprocess of etching before vanadia treatment improved creation of a uniformly dispersed compact surface Aloxide V-rich film of smooth arrival and reserved the active surface sites and thus stopping localized corrosion. Vanadate conversion coatings seem promising asalternatives to toxic chromating for the corrosion defense of Al alloys insodium chloride solution.
S.S. Pathak [8] has established a Sol-gel, Thermal-cured, waterborne organosilane-polyester coatings using polyester resin and methyltrimethoxysilane, 3-glycidoxytrimethoxysilane for increasing corrosion resistance of AA6011 AL alloy. The coatings morphological features and structural were examined by (AFM) and (FT-IR). Resultsdisplay that the coatings on Al were smooth, defect-free and continuous. Performance of the SiE coatings were examined and matched with pure polyester coating and organosilane coating using contact angle measurement, pencil hardness test and potentiodynamic polarization studies. SiE coatings provided better hydrophobicity and hardness than the polyester coating. Furthermore, polarization studies have shown that the SiE coated substrate provided a better corrosion resistance than the polyester coated substrate due creation of aluminum-oxygensiliconcovalent bond at coating-Al interface.
N. F. Atta, et al. [9] have prepared TiO 2 film by Sol-Gel and working as a corrosion protective coating for aluminum alloy(AA2024) in 3.5% sodium chloride. The coatings morphology was examined using (FESEM). The impedance spectroscopy measurements and electrochemical polarizationused to evaluate the protective nature of the coating. Modification of the sol-gel coating with titaniashow thatthe corrosion resistance of the alloy improved. Theelectrolyte penetrated with slower rate to theunderlining of the coating related to the non-permeable and insulating nature of the coating. Instead, the modification of the sol-gel structure enhancedwith presence of TiO 2 that allowed ended with a high cross-linkedstructure. However, highchance for galvanic corrosion founded with increasing the content of titanium that resulted in increasing the corrosion rate. Increasing resistance of Corrosion of the sol-gel coating includetitanium dioxide explaned byelectrochemical impedance spectroscopy measurements provided. Changes imparted tothe surface with and without coating revealed by the surface morphology before and aftercorroding solution.
F.Yu et al. [10] have modifiedsol-gel coatingcontaining hybrid titania, corrosion protection of AA2024-T3 alloyinvestigation by pigments of a co-polymer polyvinyl butyral insert to a conductive polymerpolyanilineand a corrosion resistant glass flake (GF). Coatings effect tested by (EIS) during immersion in 3.5% sodium chloride solution. Avolume ratio of sol-gel/PVB = 4:1 revealed that modification by PVB can increase the resistance to electrolyte ingress of the sol-gel layer, intermediate layer of the PANI between coating and substrate produced a chemically stable as agglomerate-type particles.Additionally,the modification of the sol-gel with GF provided a physical barrier properties to water uptake. GF increases the thermal stability anddecreases the affectedthe 624 condensation reactions taking place during the sol-gel synthesiswhich indicatedby water contact angle measurementsand (DSC/TG)analysis.
M. H.Hussin [11] has evaluated a sol-gel coatings consist of hybrid (APTES-TEOS)and single (TEOS) to investigate anti-corrosion performances of Al alloys exposed to 3.5wt% sodium chloride. electrochemical impedance spectroscopyandpoten-Tiodynamic polarizationemploying to study the effect of coating .the single precursor silanol coatingofferedthe lowestcurrent Density andcorrosion ratein comparisonwith Hybrid sol-gel coating showed by three corrosion analysis techniques.According to tafelcurves the hybrid sol gel improved performance of Al alloys against corrosion considerably.

Materials:-Substrate
In this work, a main substrate of 6061-T6 aluminum alloy has been used for coating process, the alloy has been tested by chemical composition analysis device,Table1 show the chemical composition of the alloy, Fig. 1 show chemical composition device. Table 2 contains the materials that have been used in this work.

Substrate Preparation:
The first step is cutting a rod from 6061-T6 aluminum alloy of size(15 mm )radius and (4 mm)length for each sample used as the main substrates in this investigation.The second step is grinding of samples by silicon carbide papers (220-800) using grinding and polishing device (MetaServ 250, China)as shown in fig.2 , and then 625 ultrasonically cleaned by ultrasonic cleaner(MTI corporation, USA) as shown in fig. 3 for 10 min with ethanol and distilled water.
Preparation of Nanocomposite:-Nano Composite polymer consists of epoxy/TiO 2 nanoparticles has been prepared. Liquid epoxy was blended with the hardener at weight ratio 2:1 Epoxy/Hardener . Nanoparticles of TiO 2 were added with different weight % to the blended polymer as revealed in Table 3.Themixing of Nanocomposite coating done by stirrer for 30 minutes.
The specimens have been used for applying (Epoxy:TiO 2 ) nanocomposite coating by dipping process on6061 aluminum alloy the specimens as shown in Fig.5.The dipping with automatic process has been processed at speed 200 mm/min for 10 seconds. The samples are left for curing at atmosphere condition. To study the effect of dipping speed on the behavior of corrosion, the coating condition that gave best corrosion resistance had been repeated on other specimens but with different dipping speeds as indicated in Table4.

Characterization Tests: (FESEM/EDS)
In this study, Field Emission scanning electron microscopy (TESCANMIRA 3FRANCE) Fig.6,has been used to identify the surface structure and the morphology of the coated substrates.The local chemical composition of coatings have been analyzed using EDS, which is found as an accessory with SEM.

Electrochemical test:
The test has been performed at the Ministry of Science and Technology through the employment of electrochemical system PARSTAT 2273 as shown in fig.8. Thetesting completed by Conventional three-electrode cells.Al alloy samplesthe firstelectrode as (working electrode), a reference electrodeof Ag/ AgCl (secondelectrode)using incell, and platinum is used as a counter electrode as third electrode, the three electrodes cells have been immersed in 3.5% sodium chloride solution. In this testing, fresh solutions are used for all the electrochemical tests. Also 1cm 2 areas have been left for exposure to the electrolyte. The variation of open circuit potential is measured Since the first minute of the immersion process,. The curves of the potentiodynamic polarization have been obtained at 1 mV/s .
The following equation has been used to estimate corrosion rate based on corrosion current: The Results and Discussion:-(AFM) the surface roughnessof the coated layersrevealed by(AFM )analysis. Table 5 presents the average values of the surface roughness of uncoated and coated substrates measured by AFM analysis. Table 5:-Average surface roughness obtained by AFM analysis. Fig.9 (a-e) shows the AFM images of samples. Fig. 9a revealed thathigher value of R (255.1 nm) ofuncoated substrate as compared to that of coated substrates. This indicates the significant effect of different coatings produced by dipping process on the surface of 6061-T6 alloy. On the other hand, the AFM analysis showed that the coated substrates are fully covered by nano-scale layers.
In case of epoxy, high value of Ra (24.4 nm)characterizes in topography of coating as a rough surface, having. This might be owing todecreased homogeneityand bigger agglomerations along with in the surface structure of epoxy coated substrate, as shown in Fig.9  The topography of sample 1% TiO 2 NPs coated substrate discloses a greater homogeneity, as shown in Fig. 9c. The surface of the 1% TiO 2 NPs coating issmoother (Ra= 1.508 nm) thanother films as it possesses less amount of agglomeration comparing with these coatings.
The topography of sample 3% TiO 2 NPs coated revealed that highly incorporated ofTiO 2 with epoxy. Fig.9d show thatcoatingis obtained with a nanoscale structure and higher homogeneity,along with surface roughness(Ra= 2.609 nm). In case of 5% TiO 2 NPs coating, the film is composed of nano-particles shown in fig.9e. The topography of this coating characterizes porous structure with a value of Ra (5.212 nm nm) lower to that of epoxy and uncoated substrate. The presence of larger agglomerations along with reduced homogeneity of TiO 2 partical in coated surface structure (see Fig.9) is the main factor affected on the surface roughness of this coating.  Figures 10,11,12 and 13 exhibit differentmagnifications of SEM micrographs and EDS analysis for epoxy, 1%, 3% and 5% coatings, respectively .It is expected that the properties of the films formed by dipping coating, which might be changeable in a larger extent, depend greatly on the surface morphology. Fig.10 (a & b), the epoxy coating covered the surface totally and consists of different sized irregular agglomeration (Figure2b, red arrows) This agglomeration occurs because the mixing was carried out by for short time, microcracks (Figure2b, yellow arrows) distributed on the epoxy film. the major elemental peaks of alloy and epoxy explained in (Fig.10c) corresponding to EDS analysis. Fig.11 showing low and high magnification for 1%wt TiO 2 nano composite containing .homogeneityand higher compactfor coated surface can be seen in Fig.11(a &b).Good incorporation of TiO 2 with epoxy matrix leading to enhanced homogeneity of coated surface. Fig.12demonstrates the SEM micrographs of epoxy/TiO 2 Nano composite containing 3% of TiO 2 coating in low and high magnification along with analysis of EDS of deposited film.non homogeneous structurein Fig.12 (a & b) and numerous micro-pores (Fig.12b, red arrows), and in Fig.12c, the EDX spectrum evidently shows the existence of Ti, O, Mg, Si, C and Al.

SEM-EDS Observations:-
630 Fig.13 (a & b) illustrates the SEM of epoxy/TiO 2 Nano composite containing 5% of TiO 2 . coalescence of many nanoparticles give the structural aggregates which developed on the coated surface to form coarse particles (Fig.13b, red arrows), and micro-pores (Fig.13b, black arrows). The corresponding EDX spectrum for epoxy/TiO 2 coating (Fig.13c) shows that the presence of TiO 2 coating with the presence of major peaks related to TiO 2 elements coating and AA6061 alloy , i.e. Al, Mg, Si, C, O and Ti, were detected.

A B
Ocp-Time Measurements: Fig.14 show the vales of open circuit potential for all samples .The OCPoscillated with time in the initial stages and then decreased with time until reaching to the stable potentials as observed in fig.14 .However, higher oscillations were in uncoated samples than in coated samples. Moreover, the coated samples show more noble potentials with a shift towards the noble direction. It is of a important note that the coating with 1% TiO 2 NPs exhibited the best results as in fig.14 and fig.15.

Potentiodynamic polarization:
Theepoxy /TiO 2 NPs corrosion protection performance shown in Table6 for coating properties on AA6061 electrode was investigated in 3.5% sodium chloride solution using potentiodynamic polarization measurements. Fig.16 which represents the change in polarization curve (Tafel) for different surfaces coating, we can see obviously how all the curves go toward positive direction and becomes positive than uncoated sample, i.e. more passivation tendency.    Table 6, which represent the corrosion characteristics for all samples that the anodic part (especially the passivation region) is more passive and passivation current is more close to cathodic current, i.e. the oxidation reaction on the metal surface is retarded and more difficult to reduce passivation current. The increasing in passivation is related to TiO 2 NPs concentration in epoxy coated layer. the corrosion rate for sample(epoxy without addition TiO 2 NPs ) was 9.917 ×10-3 mm/y while when the concentration was 1% the corrosion rate was 7.131×10-4 mm/y and the corrosion rate gradually decreased with increasing the TiO 2 NPs concentration in epoxy coated layers as shown in Fig.16.  Table 7 represent the change in polarization curve (Tafel) for coated samples with different dipping speeds, It is noticed that increasing the dipping speed led to decrease the corrosion and corrosion rate, that happened because the more decreasing in dipping speed led to sediment the TiO 2 NPs in dipping solution, while the increasing in dipping speed led to more TiO 2 NPs to be in the coated layer and reduce corrosion rate.