Electrodeposition of Ni-La2O3 composite on AA6061 alloy and its enhanced hardness, corrosion resistance and thermal stability

Accepted Manuscript Electrodeposition of Ni-La2O3 composite on AA6061 alloy and its enhanced hardness, corrosion resistance and thermal stability

R.K. Vishnu Prataap, S. Mohan PII: DOI: Reference:

S0257-8972(17)30614-X doi: 10.1016/j.surfcoat.2017.06.011 SCT 22422

To appear in:

Surface & Coatings Technology

Received date: Revised date: Accepted date:

12 September 2016 22 March 2017 4 June 2017

Please cite this article as: R.K. Vishnu Prataap, S. Mohan , Electrodeposition of Ni-La2O3 composite on AA6061 alloy and its enhanced hardness, corrosion resistance and thermal stability, Surface & Coatings Technology (2017), doi: 10.1016/j.surfcoat.2017.06.011

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Electrodeposition of Ni-La2O3 composite on AA6061 alloy and its enhanced hardness, corrosion resistance and thermal stability R.K. Vishnu Prataap, S. Mohan* CSIR- Central Electrochemical Research Institute, Karaikudi- 630006, India.

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Abstract

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In this work, the microstructure, microhardness, corrosion behaviour and thermal stability of NiLa2O3 composite on AA6061 aluminium alloy were studied. Corrosion behaviour was studied

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with 3.5 wt % NaCl solution at room temperature in a static electrolyte condition. Ni-La2O3 showed nobler corrosion potential than the pure nickel and aluminum alloy and a maximum

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microhardness of 750 HV (Vicker’s hardness) was observed at optimized conditions. It is evident

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that the incorporation of La2O3 in the Ni metal matrix leads to the corrosion resistance and the hardness improvement. Thermal stability was studied by using differential scanning calorimetry

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(DSC) as well as annealing at constant temperature of 500 0C for five hours in a furnace and it

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shows better thermal stability of the composite. Electrodeposited Ni-La2O3 composites were

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characterized by SEM / FESEM, EDS, XRD and electrochemical techniques. Keywords: Electrodeposition, AA6061 alloy, Ni-La2O3 composite, Differential scanning

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calorimetry, Microhardness, Corrosion resistance, Thermal stability.

1. Introduction Aluminum and its alloys are widely used in aircraft, automobiles, building extrusions and marine equipments. This is mainly because of its high strength-to-weight ratio and corrosion resistance. Aluminum is a soft metal and it has very low hardness, when small amount of Si, Mg or Mn are added to pure aluminum and its hardness and other mechanical properties are improved. Due to

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ACCEPTED MANUSCRIPT the stable Al2O3 barrier layer formation, aluminum and its alloys are protected from its environment. Although at severe conditions, it is affected by the environment [1]. In general the oxide layer on aluminum is resistant to aqueous solutions with pH values between 5 and 8. Localized corrosion (Pitting corrosion) and galvanic corrosion are most occurring corrosion

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types in aluminum and its alloys [2]. So, alternative surface coating is needed to protect from

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corrosion.

Recently, composites are attracted in a great level, due to its desirable properties with cost

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effectiveness. Metal matrix composites (MMCs) improve the hardness as well as corrosion resistance of active metals and alloys. Rare earth oxides reinforced composites are used for

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oxidation resistance, corrosion resistance and thermal barrier coatings in the form of MMCs or

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paints. CeO2, ZrO2 are widely studied rare earth oxides [3,4]. Organic coatings such as silanes and resins are mostly investigated surface coatings for aluminum and its alloys for its corrosion

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protection, whereas metallic coatings enhance the hardness of aluminum alloys. But, ceramics

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reinforced metal matrix composites further increases the hardness as well as the corrosion resistance. A variety of oxides (TiO2, SiO2, Al2O3, CeO2, ZrO2, SnO2 and Cr2O3), [5-11] carbides

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(SiC,WC and TiC) [12-21] and nitrides (BN and Si3N4) [22-25] are used in the electrodeposition

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of nickel composites because electroplated nickel possess minimum porosity with better corrosion and wear resistance among the other commonly used non noble metallic coatings [26,27].

2. Experimental Aluminum (AA6061) alloy of the dimension 70 x 20 X 2 mm (4 cm2 working area) was used as a cathode and nickel with the dimension of

80 x 30 x 10 mm was used as anode.

Electrodeposition was carried out with a two electrode set up. Milli-Q water (18.2 Mohm.cm) 2

ACCEPTED MANUSCRIPT was used to make all the electrolytes. All the electrochemical measurements were carried out by using Autolab PGSTAT 30 potentiostat–galvanostat electrochemical workstation. Saturated calomel electrode and platinum foil (2.25 cm2) were used as reference and counter electrodes respectively. Impedance spectra are recorded in the frequency range 100 kHz to 10 mHz.

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Polarization curves are recorded in the potential range of -1 V to 1 V vs open circuit potential

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with the scan rate of 2 mV s-1. La2O3 nanopowder (< 50 nm) was purchased from Sigma Aldrich

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and used as it is received. All the experiments were carried out at room temperature. The La2O3 nanopowder is dispersed in a conventional Watt’s nickel electrolyte. Scanning electron

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microscopy (SEM- Tescan), and X-ray energy dispersive spectroscopy (EDS) were obtained

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from ZEISS SUPRA 55VP coupled with OXFORD X-MAX 20 mm2. X-ray diffractions (XRD) were obtained from Bruker. Thickness of the coating and microhardness were measured by

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PosiTest thickness meter and Everone MH 100 microhardness tester respectively.

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2.1. Bath composition and plating conditions: - 240 g dm-3

Nickel chloride

- 30 g dm-3

Boric acid

- 35 g dm-3

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Nickel sulfate

Sodium lauryl sulfate

- 0.3 g dm-3

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Particle content (La2O3) - 5- 50 g dm-3 Stirring rate

pH and Temperature

- 350 rpm - 3.5 & 25-30 0C

Current density

- 1- 5 A/dm2

Bath volume

- 400 ml

Anode & Cathode ratio – 2:1

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3. Results and Discussion 3.1. Electrolytic bath preparation and electrodeposition The lanthanum oxide nano powder was dispersed into the conventional watts nickel electrolyte

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and kept for stirring (700 rpm) to 8 hours prior to electrodeposition. The particle content was

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varied up to 50 g dm-3 with the successive addition of 5 g dm-3 to the bath. Before plating, the

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cathode platelets were cleaned with acetone and 1M NaOH. Cleaned cathodes were immediately dipped into the zincating solution (concentrated sodium zincate) for about 60 seconds and then

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Ni-La2O3 plating was done. Zinc is less negative than aluminum and it can form immersion

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deposit on aluminum and its alloys. While zincating, a low thick (typically 1 or 2 microns) Zn film is formed on the aluminum surface and subsequently it allows the adherent electrodeposits.

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Aluminum also dissolves when immersing into the concentrated sodium zincate solution,

Coating uniformity, thickness and stirring rate optimization

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3.2.

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although the rate of Zn deposition exceeds the aluminum dissolution.

The stirring rate of the magnetic stirrer was optimized based on the appearance of the composite

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film. Incorporation of La2O3 is also determined by the stirring rate, which is confirmed by EDS

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analysis. At higher speed (rpm), the Ni-La2O3 was not dispersed uniformally and the optimized stirring rate is 350 rpm to this dimension of the bath. Coating thickness was measured by PosiTest thickness meter as an average of three values at different places.

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Surface morphology and composition

Fig.1 shows the SEM images of Ni-La2O3 nanocomposite deposited from 5, 10, 15 and 20 gram per litre La2O3 dispersed baths at a current density of 3A/dm2. The pure Ni exhibits pyramidal like surface morphology whereas the incorporation of lanthanum oxide into the nickel matrix, 4

ACCEPTED MANUSCRIPT hemispherical like nucleation occurs with the increase in percentage of La2O3 and reduction of nickel grain size was observed (Fig. 1(a-d)). In the presence of lanthanum oxide, the electrocrystallization mode is changed due to the adsorption of Ni2+ with La2O3. Initially, the incorporated oxide particles reduce the electrical surface area of the cathode and subsequently,

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the ad-ions alter the nucleation of nickel. In the electrodeposition process, grain size of the metal

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is determined by two factors, i.e. (a) low overpotential with high surface diffusion rates (b) high

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overpotential with low diffusion rates [28, 29]. Thus, the more La2O3 incorporated nickel matrix exhibit small grain size. Fig. 2 shows the FESEM image and EDS spectrum of the cross section

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of Ni-La2O3 composite.

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Fig. 3 shows the EDS spectrum of Ni-La2O3 deposited from 15 g dm-3 lanthanum oxide dispersed

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bath at a current density of 3A/dm2, which is the maximum weight percentage of La2O3 obtained in the deposit when compared to other plating conditions. Fig. 6 gives the weight percentage of

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lanthanum oxide at various current densities in an optimized bath composition. Fig. 4 shows the

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XRD pattern of nickel lanthanum oxide composite. The 111, 002, 022 planes correspond to the nickel (Ref. code: 98-006-2720) and 013, 002, 123, 011 are to lanthanum oxide (Ref. code: 98-

Microhardness

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3.4.

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005-1123) respectively.

The effect of current density and particle content in the bath were analyzed. Microhardness of the composite was found in the range of 425 HV to 700 HV at optimized conditions. Fig. 5 shows that the microhardness increases with current density up to certain level then it decreases to low value. Initially the solid oxide particle content in the bath was low and the inclusion percentage of oxide particle into the metal matrix was also very low and this is due to the low surface coverage of the adsorbed oxide particles on the cathode surface. While increasing the amount of 5

ACCEPTED MANUSCRIPT particle content the amount of adsorption also increased and at particular concentration the adsorption attains the saturation level and further increase of the oxide particle lowers the adsorption of the particles at the cathode so that the amount of incorporation is decreased. The solid oxide particles reinforce the hardness of the nickel matrix. Fig. 7 correlate the weight

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percentage of La2O3 at a particular current density as well as particle content dispersed in to the

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bath. Thus, the oxide particle content affects the nucleation mode of nickel by altering the double

Corrosion behavior

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3.5.

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layer structure, so that the composite film possesses enhanced hardness.

Electrochemical polarization studies were done in 3.5 wt % NaCl solution for AA6061 alloy,

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pure nickel and Ni-La2O3 composite coated samples. The polarization curves (Fig.8.) were

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recorded in the potential range from -1 V to 1 V at a scan rate of 2 mV s-1. In order to get the stable open circuit potential (OCP), the three electrode cell was kept around 20 minutes for

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equilibrium. La2O3 incorporated nickel composite shows different corrosion behavior than pure

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nickel because the oxide particle affects the nucleation of nickel. The higher weight percentage of lanthanum oxide showed nobler potential than the bare and pure nickel. The corrosion

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potential (Ecorr), corrosion current (Icorr) and corrosion rate are given in the table 1. Polarization

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curves revealed that the prepared composite film shows 687 mV more positive Ecorr than the bare substrate and also the Icorr value considerably low (0.9 µA). The outer layer is nickel lanthanum oxide composite and the possible reaction is nickel dissolution in the corrosion process. Pitting corrosion is mostly occurring in aluminum and its alloys in the chloride media. Porosity of the coating is reason for pitting corrosion. In the potentiodynamic polarization curves, oxygen reduction is the cathodic reaction and nickel dissolution is the anodic reaction. Porosity is calculated from the below equation, 6

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P=

∆Ecorr R ps X 10−( bA ) Rp

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P – Porosity (%)

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Rp -- Linear polarization resistance of the coated sample

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Rps – Linear polarization resistance of the substrate (bare)

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ΔEcorr – Difference between the corrosion potentials of coated and bare

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bA – Anodic Tafel slope of the bare

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The value of porosity (P) = 0.0016 and this value indicates that the coating is very compact and pore free. So that, the composite coating efficiently prevents the corrosion of aluminum alloy

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6061.Fig. 9 shows the impedance spectra of Ni-La2O3 deposited at different current densities (1

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to 5 A/dm2). The charge transfer resistance (Rct) increases with the lanthanum oxide weight percentage. Inclusion of oxide particle into the nickel matrix, generally reduce the grain size of

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nickel and also increase the charge transfer resistance. Rct values increase up to 3 A/dm2 and then decreases, it is coincides with EDS as well as polarization data which indicate that the weight percentage of La2O3 influences to corrosion resistance. (see Table 1.)

3.6.

Differential scanning calorimetry

In order to understand the thermal stability of the composite, differential scanning calorimetry (DSC) was recorded. DSC is often used for analysis of solid state reactions, such as precipitation, 7

ACCEPTED MANUSCRIPT homogenisation, devitrivication and recrystallisation; and solid–liquid reactions, such as incipient melting and solidification. Fig. 10 Depicts the heat flow vs temperature curve in which the appreciable heat flow is observed beyond 600 0C. Moreover, annealing was also done in a furnace at the temperature of 500 0C. The SEM images (Fig. 11) show that the morphology of AA 6061, surface

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the composite is almost same after the heat treatment but in the case of bare

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cracks and oxide particle growth were also observed after heating at 500 0C for five hours. The

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phase changes during the heat treatment is studied with XRD (Fig. 12) and it is clearly indicate the ratio between 111 and 002 planes, 111 and 022 planes of nickel remain before and after the

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heat treatment. This indicates the thermal stability of the Ni-La2O3 composite.

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Conclusions

We have varied the electrolyte composition, current density, stirring rate and particle content for

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the Ni-La2O3 composite plating on aluminum alloy. The optimum current density and particle

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content for maximum incorporation (7.6 wt %) of lanthanum oxide particle is found to be

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3A/dm2 and 15 gram per litre La2O3 respectively. FESEM/SEM, EDS and XRD confirmed that the La2O3 incorporated nickel matrix and the co-deposited lanthanum oxide controls the grain

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size of nickel. This is the reason behind the improvement of hardness up to 750 HV. Potentiodynamic polarization curves and impedance spectra reveal the corrosion resistance of

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Ni-La2O3 composite. Thermal stability at 500 0C of the composite was evaluated by SEM and XRD. SEM images showed the surface morphology is almost retained after the heat treatment and there were no appreciable phase changes observed in XRD and thus the composite film shows excellent thermal stability. The composite film improves the hardness as well as corrosion resistance and thermal stability of the aluminum alloy.

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Acknowledgements This work is supported by the Council of Scientific and Industrial Research- India through the project CSC-0132. The authors thank to Dr.Vijayamohanan K Pillai, Director, CSIR-CECRI for

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his support.

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References

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[1] Joseph R. Davis, Corrosion of Aluminum and Aluminum Alloys, ASM International, (1999). [2] Dietrich G. Altenpohl, Aluminum: Technology, Applications and Environment- A profile of

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modern metal, The Aluminum Association, Inc. Washington DC, (1998).

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[3] Z.H. Xu, X. Zhou, K. Wang, J.W. Dai, L.M. He, Thermal barrier coatings of new rare-earth composite oxide by EB-PVD, J. Alloys Compd, 587 (2014) 126–132.

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[4] G. Di Girolamo, C. Blasi, A. Brentari, M. Schioppa, Microstructural, mechanical and thermal characteristics of zirconia-based thermal barrier coatings deposited by plasma spraying, Ceram. Int., 41(9) (2015) 11776–11785.

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[5] J.M. Hu, L. Liu, J-Q. Zhang, C-N Cao, Electrodeposition of silane films on aluminum alloys for corrosion protection, Prog. Org. Coat., 58 (2007) 265–271.

CE

[6] H. Ferkel, B. Müller, W. Reihemann, Electrodeposition of particle-strengthened nickel films Mater. Sci. Eng. A 234 (1997) 474-476.

AC

[7] M.H. Fawsy, M.M. Ashour, A.M. Abd El-Halim, Trans. Inst. Met. Finish. 74 (1996) 72. [8] Z. Xiaowei, S. Yifu, Z. Yingying, J. Huiming, Mechanism and microstructure of nickel-ceria composite coatings prepared by pulse current deposition under the ultrasonic field, J. Rare Earths 29 (2011) 883-887. [9] W. Wang, F.Y. Hou, H. Wang, H.T. Guo, Fabrication and characterization of Ni– ZrO2 composite nano-coatings by pulse electrodeposition, Scripta Mater. 53 (2005) 613-618. [10] I. Ul-Haq, T.I. Khan, Tribological behavior of electrodeposited Ni–SnO2nanocomposite coatings on steel, Surf. Coat. Technol. 205 (2011) 2871-2875.

9

ACCEPTED MANUSCRIPT [11] K. Kumar, R. Chandramohan, D. Kalyanaraman, Effect of heat treatment on cobalt and nickel electroplated surfaces with Cr2O3 dispersions, Appl. Surf. Sci. 227 (2004) 383-386. [12] S.C. Wang, W.C.J. Wei, Kinetics of electroplating process of nano-sized ceramic particle/Ni composite, Mater. Chem. Phys. 78 (2003) 574-580.

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[13] P. Nowak, R.P. Socha, M. Kaisheva, J. Fransaer, J.P. Celis, Z. Stoinov, Electrochemical investigation of the codeposition of SiC and SiO2 particles with nickel, J. Appl. Electrochem. 30 (2000) 429-437.

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[14] G. Maurin, A. Lavanant, Electrodeposition of nickel/silicon carbide composite coatings on a rotating disc electrode, J. Appl. Electrochem. 25 (1995) 1113-1121.

US

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[15] K. Helle, F.C. Walsh, Electrodeposition of Dispersion Composite Coatings Based Upon Polymer and Ceramic Particles in a Metal Matrix, Transactions of the Institute of Metal Finishing, 75(2), (1997), 53-58.

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[16] C. Kerr, B.D. Barker, F.C. Walsh, J. Archer, The Electrodeposition of Composite Coatings based on Metal Matrix-Included Particle Deposits, Transactions of the Institute of Metal Finishing, 78(5), (2000), 171-178.

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[17] C.T.J. Low, R.G.A. Wills, F.C. Walsh, Electrodeposition of Composite Coatings containing Nanoparticles in a Metal Deposit, Surface & Coatings Technology, 201, (2006), 371-383.

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[18] F.C. Walsh, C. Ponce de León, A Review of the Electrodeposition of Metal Matrix Composite Coatings by Inclusion of Particles in a Metal Layer: An Established and Diversifying Coatings Technology, Transactions of the Institute of Materials Finishing, 92, (2014), 83-98.

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[29] P. Gyftou, E.A. Pavlatou, N. Spyrellis, K.S. Hatzilyberis, Trans. Inst. Met. Finish. 78 (2000) 223.

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[20] P. Gyftou, M. Stroumbouli, E.A. Pavlatou, N. Spyrellis, Trans. Inst. Met. Finish. 80 (2002) 88. [21] P. Gyftou, E.A. Pavlatou, N. Spyrellis, Effect of pulse electrodeposition parameters on the properties of Ni/nano-SiC composites, Appl. Surf. Sci. 254 (2008) 5910-5916. [22] M. Stroumbouli, P. Gyftou, E.A. Pavlatou, N. Spyrellis, Codeposition of ultrafine WC particles in Ni matrix composite electrocoatings, Surf. Coat. Technol. 195 (2005) 325-332. [23] D.K. Singh, V.B. Singh, Electrodeposition and characterization of Ni–TiC composite using N-methylformamide bath, Mater. Sci. Eng. A 532 (2012) 493-499.

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[24] M.A. Khazrayie, A.R.S. Aghdam, Si3N4/Ni nanocomposite formed by electroplating: Effect of average size of nanoparticulates ,Trans. Nonferrous Met. Soc. China 20 (2010) 1017-1023. [25] C.M.P. Kumar, T.V. Venkatesha, Electrodeposition, characterization and corrosion behavior of Ni–Si3N4 composites, Phys. Scr. 86 (2012) 015804.

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[26] E. Pompei, L. Magagnin, N. Lecis, P.L. Cavallotti, Electrodeposition of nickel–BN composite coatings, Electrochim. Acta 54 (2009) 2571-2574. .

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[27] T. Lampke, B. Wielage, D. Dietrich, A. Leopold, Details of crystalline growth in codeposited electroplated nickel films with hard (nano) particles, Appl. Surf. Sci. 253 (2006) 2399-2408.

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[28] AG McCormack, MJ Pomeroy, VJ Cunnane, Microstructural Development and Surface Characterization of Electrodeposited Nickel/Yttria Composite Coatings, J. Electrochem Soc. 150 (5) (2003) c356- c361.

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[29] Adel M.A. Mohammed and Terasa D.Golden., Electrodeposition of Composite Materials, ISBN: 978-953-51-2270-8.

Figure Captions:

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Fig. 1. SEM images (a-d) of Ni-La2O3 at 5,10,15, 20 g dm-3 La2O3 dispersed bath at the current density of 3A/dm2

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Fig. 2. FESEM image of cross sectional view with EDS spectrum Fig. 3. EDS spectrum of Ni-La2O3 at 15g dm-3 La2O3 content (Top surface)

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Fig. 4. XRD pattern of Ni-La2O3 deposited from 15 g dm-3 La2O3 at the current density of 3A/dm2 Fig. 5. Microhardness of Ni-La2O3 at various current densities at optimized bath compositions Fig. 6. Amount of La wt % at different deposition current densities Fig. 7. Weight percentage of La2O3 at different concentration of La2O3 content at various current densities Fig. 8. Potentiodynamic polarization curves of bare AA6061, Pure Ni and Ni-La2O3 composite coated AA6061 alloy, recorded from 3.5 wt % NaCl solution. 11

ACCEPTED MANUSCRIPT Fig. 9. Impedance spectra of Ni-La2O3 electrodeposited at different current densities. (15 g dm3 particle content, 3 A/dm2 current density) Fig. 10. Differential scanning calorimetric curve of Ni-La2O3 composite Fig. 11. SEM images of before and after annealing the Ni-La2O3 coated AA6061 alloy and bare AA6061 alloy. (a: before annealed Ni-La2O3coated AA 6061, b: after annealed Ni-La2O3 coated AA 6061, c: before annealed bare AA6061, d: after annealed bare AA6061).

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Fig. 12. XRD patterns of before and after heat treatment of Ni-La2O3 and AA6061 alloy. A: After heat treated Ni-La2O3 at 500 0C, B: without heat treated Ni-La2O3, C: After heat treated AA6061 alloy, D: without heat treated AA6061 alloy. La2O3 • Ni ♦ Al2O3 ‫٭‬

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Table. 1 Corrosion rate values corresponding to the polarization curves (Fig. 7)

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Figures and Captions:

Fig.1. SEM images (a-d) of Ni-La2O3 at 5,10,15, 20 g dm-3 La2O3 dispersed bath at the current density of 3A/dm2

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Fig. 2. FESEM and EDS spectrum of Ni-La2O3 composite at 15 g dm-3 La2O3 content. ( In cross sectional view- yellow square indicates the EDS taken location)

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Fig.3. EDS spectrum of Ni-La2O3 composite at 15g dm-3 La2O3 content (Top surface)

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Fig.4. XRD pattern of Ni-La2O3 deposited from 15 g dm-3 La2O3 at the current density of 3A/dm2

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Fig.5. Microhardness of Ni-La2O3 at various current densities at optimized bath composition

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Fig.6. Amount of La wt % at different current densities

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Fig.7. Weight percentage of La2O3 at different concentration of La2O3 content at various current densities 19

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Fig.8. Potentiodynamic polarization curves of bare AA6061, Pure Ni and Ni-La2O3 composite coated AA6061 alloy, recorded from 3.5 wt % NaCl solution. 20

Sample

Pure Ni coated AA6061

(mm / year) 14.08 x E-5

1.515

-1.14

9 x E-5

1.410

-0.83

0.9 x E-6

0.170

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Ni-La2O3 coated AA6061

Corrosion rate

-1.517

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AA6061

icorr (A)

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Ecorr (V)

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Table. 1. Corrosion rate values corresponding to the polarization curves

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Equivalent circuit

Fig.9. Impedance spectra of Ni-La2O3 electrodeposited at different current densities. (15 g dm-3 particle content, 3 A/dm2 current density), Inset: Magnification at high frequency range 22

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Fig.10. Differential scanning calorimetric curve of Ni-La2O3 composite

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Fig. 11. SEM images of before and after annealing the Ni-La2O3 coated AA6061 alloy and bare AA6061 alloy. (a: before annealed Ni-La2O3coated AA 6061, b: after annealed Ni-La2O3 coated AA 6061, c: before annealed bare AA6061, d: after annealed bare AA6061).

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Fig. 12. XRD patterns of before and after heat treatment of Ni-La2O3 and AA6061 alloy. A: after heat treated Ni-La2O3 at 5000 C, B: without heat treated Ni-La2O3, C: after heat treated AA6061 alloy, D: without heat treated AA6061 alloy. La2O3 • Ni ♦ Al2O3 ‫٭‬

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Highlights:

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1. Electrolyte composition and plating parameters were studied for lanthanum oxide reinforced nickel metal matrix composite on AA6061 alloy. 2. The agitation speed and oxide particle content in the bath are the main parameters in the composite plating. 3. Rare earth oxide reinforced composites not only improves the corrosion resistance but also the hardness and thermal stability.

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