Effect of Magnetic Field on Corrosion Performance of Ni–Co Alloy Coatings

The corrosion protection efficacy of Ni–Co alloy coatings was tried to improve by magnetoelectrodeposition (MED) approach. The magnetic field of varying strength (B) was applied in perpendicular and parallel to the direction of diffusion of metal ions, simultaneously to the process of deposition. The corrosion behaviour of the deposited coatings was studied through electrochemical DC method and results revealed that Magneto-electrodeposited (MED) Ni–Co alloys coatings were found to be more corrosion resistant than their conventionally electrodeposited (ED) counterparts. Moreover, the effect of magnetic field is more pronounced in perpendicular field direction and was explained by Lorentz force. Under optimal condition, MED Ni–Co alloy coating obtained at a magnetic field intensity of B = 0.3 T (Perpendicular) was found to be less prone to corrosion than its ED alloy (B = 0 T) counterpart. The increased limiting current density (iL) of Co2+ ions in turn increases the corrosion resistant properties of MED Ni–Co alloy coatings. The effect of magnetic field on improved corrosion resistance of the deposited coatings have been investigated in terms of their changed surface morphology, composition, phase structure and surface roughness using Scanning electron microscopy (SEM), Energy dispersion spectroscopy (EDS), X-Ray diffraction (XRD) technique and Atomic Force Microscopy (AFM) respectively.


Introduction
The Ni-Co alloys have been widely used in variety of corrosion resistant application including aircraft gas turbines, nuclear power plant system, chemical and petrochemical industries [1]. They have been used in recorder head materials and computer hard drives as corrosion resistant materials and also emerging as good engineering materials due to their uniqueness in corrosion wear resistance and magnetic properties [2][3][4][5][6]. Recently Ni-Co coatings have been used in micro lenses to increase brightness effect [7]. In this regard, surface properties of the Ni-Co materials were modified by employing different techniques like electrodeposition, electroless plating, physical vapor deposition (PVD) and chemical vapor deposition (CVD) processes. Among this method, electrodeposition is the best technique to produce series of Ni-Co alloy coating for various corrosion resistant applications. The electrodeposition of Ni-Co alloy coatings gained tremendous attention in researchers due to their wide spread applications, and ease of fabrication [8]. Further, properties of the deposited coatings can be varied by altering the bath variable and composition with the advent of magnetoelectrodeposition process [9].
The effect of composition on magnetic properties of the Ni-Co alloy coatings was studied [10]. Another group studied the effect of current density on magnetic properties of Ni-Co alloy coatings [11]. Usually, current density is an important variable in electrodeposition process. The variation of current density in Ni-Co sulphate bath was preferred for electrodeposition process, due to their non-polluting and inexpensive behaviour [12]. It is appropriate to recall here that the difference in standard electrode potential of Ni and Co is about 0.05 V. Hence, Ni-Co electroplating follows anomalous type of codeposition, where percentage of Cobalt content in deposit is more as compared to Nickel [13]. This phenomenon of preferential deposition of less noble metal (Co), compared to more noble metal (Ni) was attributed to the formation hydroxide of less noble metal on the surface of substrate. This phenomenon was described and classified by Brenner [14]. The mechanism of deposition of Ni-Co alloy have been improved by controlling the deposition parameter such as temperature, pH value, current density and also by changing the mass transfer process at the cathode [15]. The modulation in mass transfer could be done with the help of magnetic field effect. In this direction, from the literature only few reports are available with respect to the effect of magnetic field on Cobalt and Co-Ni alloy electrodeposition for corrosion resistant applications [16][17][18]. In this regard, present paper explains about inhibition of anomalous behaviour of Ni-Co alloy coatings by the application of magnetic field at constant effect of current density. Hence, magnetoelectrodeposition was used as a best tool to improve the corrosion resistant property of the mild steel materials.
The review of magnetic field effect on electrodeposition was done by Fahidy. In this method, diffusion of ion towards cathode was controlled by the variation of magnetic field strength, which enables change in mass transport mechanism at the cathode and also this effect plays an important role in changing the microstructure of the deposited coatings at different magnetic field strength in different direction [19][20][21][22]. The application of magnetic field brings about changes in mode of electrodeposition and develops new materials with definite composition of Ni-Co alloy coatings for corrosion resistant applications. The impact of this effect on deposit characteristic mainly dependant on direction (perpendicular and parallel) and intensity of applied magnetic field. Hence, this paper detailed about the study of magnetic field effect in parallel and perpendicular direction to the flow of ions, at different magnetic field intensities with constant current density on a corrosion performance of Ni-Co alloys on mild steel.

Materials and Methods
The chemicals of analytical grade was dissolved in double distilled water. The Hull cell method was used for the optimization of Ni-Co electrolytic bath and its composition are given in the Table 1. The study revealed that current density values are in the range of 1.0-4.0 A dm −2 . The pH of the bath was maintained using pH Meter (Systronics-362) at desired value 3.4, by adding either HCl, or NH 4 OH, depending on the requirement after each deposition. The added glycerol enhances the brightness of the coatings. The simple designed electrolytic cell was used for electrodeposition process. Prior to deposition, the mild steel strips were pretreated with 10% sulfuric acid and pickled with 1:1 HNO 3 acid. The surface of the mild steel is mechanically polished with bench polisher and degreased with Trichloroethylene and washed with water. Further, pure surface was used for electrodeposition process. During deposition, Nickel was used as anode and mild steel as cathode and both were kept at a distance of 5 cm. The electrodes were dipped in optimized bath and deposition was carried out different current densities and magnetic field intensities in electrodeposition and magnetoelectrodeposition process, respectively.

Characterization
The electrodeposited and magnetoelectrodeposited coatings were studied for its surface morphology and composition using Scanning Electron microscopy (SEM) using (EVO18 from Carl Zeiss, Germany) with Energy Dispersive X-ray spectroscopy (EDS) facility (Oxford EDS (X-act). The phase information of alloy coatings were analysed using X-ray diffraction (XRD) study (Rigaku-miniFlex 600) and surface roughness of the coatings was measured using Atomic Force Microscopy (AFM, Innova SPM Atomic Force Microscope).

Electrochemical Characterization
The corrosion performances of the deposited coatings were evaluated by Potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS) methods. Here for convenience, electrodeposited and magnetoelectrodeposited Ni-Co alloy coatings are represented as ED (Ni-Co) and MED (Ni-Co) alloy coatings, respectively. Further, conventional electrodeposited coatings represented as (Ni-Co) x where x-represents the c.d. at which deposition was carried out from the optimized bath and magnetoelectrodeposited Ni-Co alloy coatings are conveniently represented as (Ni-Co) 4.0/BT/Per or para, where subscript represent the c.d. and magnetic field intensity (B = 0.1, 0.2, 0.3 and 0.4, depending on the direction). The corrosion study of ED and MED coatings was studied in 5% NaCl using an instrument VersaS-TAT3 (Princeton Applied Research). The potentiodynamic polarization study was done in a potential range of ± 250 mV at a scan rate of 1mVsec −1 . The impedance study was done in the frequency range of 100 kHz-10 mHz, with perturbing sine wave of 10 mV amplitude. The impedance plots were fitted and analysed using the Z-view software.

Electrodeposition and Characterization of Ni-Co Alloy Coatings
The electrodeposition was carried out at four different current densities from 1.0 to 4.0A dm −2 . The deposited series of coatings were studied for its composition, surface morphology, phase analysis, surface roughness and electrochemical characterization.

Compositional Analysis
The composition of the deposited Ni-Co alloy coatings were reported in Table 2. The change in the wt. % of constituting metals of the alloy, i.e., Ni and Co with increase of c.d. is as shown in Fig. 1. It was observed that at lower current density limit, i.e., at 1.0 A dm −2 , wt. % of Co in the deposit is higher than the wt.% Ni (noble metal) in the deposit. It evidences the fact that Ni-Co bath follows anomalous type of codeposition. But as the c.d. increases, wt. % Co in the deposit decreases with increase of wt. % Ni in the deposit [23]. This peculiar behaviour of the bath with respect to current density is attributed to low concentration of Co in the bath. As a result, decrease of transition c.d. of the cobalt ions was observed [24]. At higher current density, Ni deposition is kinetically controlled whereas content of cobalt is controlled through diffusion process. Therefore, on increasing the current density, discharge of Ni +2 ions are more favoured, with transfer of electrons. This in turn decreases the Co content of the alloy [24].

Surface Morphology
The surface morphology of Ni-Co alloy coatings at different c.d.'s is shown in the Fig. 2. It was observed that the surface morphology of the alloy coating changed drastically with increase c.d., as shown from The uniformity of the coating was found to be increased with increase of deposition current density. The granular structure of alloy coatings has changed to more uniform and fine-grained at higher current density, which is as shown in Fig. 2d. This change is attributed to decrease of cobalt content with increase of current density [25]. The morphology of the coatings also revealed that applied current density influences on surface smoothness of the coatings. The smoothness of the coating was enhanced with increase of current density along with decrease of granular size. Hence, c.d. has vital role on the microstructure of the alloy coatings.

X-ray Diffraction Study
The phase structure of the electrodeposited Ni-Co alloys, developed under varying conditions of current densities were studied through X-ray diffraction (XRD) analysis. Identification of different phases of the electrodeposited alloy coatings, corresponding to different c.d.'s was obtained from   (220) planes of fcc structure of Ni(JCPDS 04-0850). One more distinct peak at 73.9° belongs to (311) plane of reflection of CoNiO 2 (JCPDS10-0188). Increase or decrease in Intensity of the peaks with c.d. without any significant change in the diffraction angle indicates that Ni-Co alloy coatings form a single-phase solid solution of Co in Ni with slightly different compositions, without change in the phase structures [26] The increase in intensity of peak corresponding to (220) plane may be attributed to the change in the phase composition of alloy. In other words, Ni content of the alloy increases with c.d. and was supported by composition data as shown in Table 2. The XRD study revealed that formation of alloy costings on the surface of mild steel materials. The average grain size of alloy coating was found to be 32 nm, calculated from full width at half maximum (FWHM) of all peaks using Debye-Scherrer formula [27], given by Eq. (1). where D = crystallite size (nm), λ = 1.5406 A°(Cu K α radiation) is the wavelength of X-ray used, K = 0.9(Debye coefficient), β = full width at half maximum (FWHM) in radian and θ = Bragg's angle(Degree).

Corrosion Study
The electrochemical characterization of conventional Ni-Co alloy coatings was carried out using Potentiodynamic Polarization and Electrochemical impedance spectroscopy (EIS) methods.

Potentiodynamic Polarization Study
The three-electrode system was used to check corrosion behaviour of Ni-Co alloy coatings. The electrode assembly in which electroplated specimens are used as working electrode, platinum as counter electrode and saturated calomel electrode as reference electrode. Tafel's extrapolation method was used to calculate to corrosion rates (CR's) of the deposited coatings and corresponding Tafel plots are shown in the Fig. 4. The corrosion potential (E corr ), corrosion current density (i corr ) and CR's values for the coatings are reported in the Table 2.
T h e d a t a r e ve a l e d t h a t c o r r o s i o n r a t e increases in t he order of (Ni-Co) 4 Th is behaviour of the coa tin gs is attributed to the change in Co content with curre nt den sity and subsequently prevents the corrosion of the deposited coatings [28]. The Ni-21.8% Co coating obtained at a current density 4.0Adm −2 was found to be more corrosion resistant as compared with other lower current density coatings. Hence, cobalt content has a significant role to prevent corrosion of mild steel materials [29].

Electrochemical Impedance Spectroscopy (EIS) Study
EIS study of Ni-Co alloy coatings was carried out at different current densities and corresponding impedance plots are as shown in the Fig. 5. The single charge transfer process of Ni-Co alloy coatings was confirmed by single diameter circle involved in the plots [30]. Further, width of semicircle proportionately varies with charge transfer resistance (R ct ), which in turn increases the corrosion resistance of the base materials [31]. Hence, coating obtained at a c.d of 4.0A dm −2 showed less corrosion rate with higher value of (R ct ) as compared to other c.d coatings. This is due to the fact that with increase of current density, ion diffusion process got decreases and it affects the mechanism of corrosion [32] and corresponding R ct values are reported in the Table 2.
The ECE fitting corresponding to optimal c.d.

Magneto-Electrodeposition and Characterization of Ni-Co Alloy Coatings
In magnetoelectrodeposition process, magnetic field was induced in perpendicular and parallel direction to the flow of ions to enhance the surface and corrosion resistant properties of the coatings. The deposition was carried out at different magnetic field intensities in the range of 0.1-0.4 T. The electrode set up was placed between the two poles of magnet. The schematic representation of deposition process was as shown in the Fig. 6.

Potentiodynamic Polarization Study
The potentiodynamic polarization curves for parallel and perpendicular deposited MED Ni-Co coatings, are as shown in Figs. 7 and 8. The corrosion rates (CR's) of magnetoelectrodeposited Ni-Co alloy coatings were listed in Table 3. From the corrosion data, it was clear that the corrosion rates of MED Ni-Co alloy coating decreases sequentially with increase of B till 0.3 T, and increases thereafter in both parallel and perpendicular direction of B. From Table 3, it may be noted that superimposition of B on the process of electrodeposition increases the Ni (noble metal) content of the alloy from 78.20 to 87.86%. It is interesting to note that CR of MED Ni-Co alloy coating decreases with increase of intensity of B. This is attributed to the increase of Co content of the alloy in MED coatings. The increase in cobalt content was observed with increase of B, which was reasoned by the fact that Co is more magnetically active than Ni. In other words, Cobalt is highly magnetically active than nickel [33]. The magneto-convection effect at higher field intensities decreases the nickel content of the alloy and which in turn decreases the CR of the deposited coatings. However, when magnetic field B, higher than its limiting value (of the bath) is applied it throws an adverse effect on the deposit characters, due to increase of hydrogen evolution reaction (HER) at optimal c.d. Therefore, at higher limits of induced B (at 0.4 T), the coatings were found to be more porous, and shows more CR, in both parallel and perpendicular B. (Table 3). Thus, it may be summarised that MED (Ni-Co) 4.0/0.3 T/Per coating exhibits least corrosion rate (2.1 × 10 -2 mm y −1 ) as compared to (Ni-Co) 4

Electrochemical Impedance Study
The impedance behaviour of MED (Ni-Co) alloy coatings, under the effect of both parallel and perpendicular B were studied, and are as shown in Figs. 9 and 10, respectively. The Nyquist plots are characterized by single semicircle, which gives information about charge transfer resistant values. It may be seen that in both parallel and perpendicular B, width of the semicircle got increases till 0.3 T and then got decreases to 0.4 T. The ECE circuit for optimal coatings i.e., (Ni-Co) 4 Table 4. From the data, it was clear that the charge transfer resistance (R ct ) of MED coatings increases with intensity of B. The value of R ct was found to be decreases, due the increase in speed of diffusion of ions at higher field intensity B = 0.4 T. Hence, minimum Rct value, increases the corrosion rate of the deposited coatings. On comparing axial radii of semicircles, corresponding to MED (Ni-Co) alloy coatings of different configurations (both in intensity and direction of B), it may be concluded that MED (Ni-Co) 4.0/0.3 T/Per coating was found to be more corrosion resistant, due to higher value of R ct .

XRD Study
The XRD patterns for MED Ni-Co alloy coating obtained at different field strengths, under parallel and perpendicular direction are given in the Figs. 11 and 12. It may be noted that XRD patterns of all MED Ni-Co alloy coatings remains same, regardless of the intensity and direction of B. However, the intensity of reflection was found to be changed with change in the magnetic field intensities. Thus, XRD study of MED Ni-Co alloy coatings, under both parallel and perpendicular B, reveals that applied magnetic field has a vital role on the composition of the alloy, but not with the phase structure of alloy. This confirms that fact that magneto electrodeposition of Ni-Co alloy coating is diffusion or magnetic field controlled at different field intensities. The constancy of phase structure of Ni-Co alloy coatings with direction and intensity of B may be explained as follows: The Ni-Co alloys, it is known that the electrochemically deposited Ni-Co alloy can form a solid solution of Co in a nickel matrix (up to 25 wt.% Co) [36].In the present study, Ni-Co alloy containing less than 25 wt.% Co forms a single-phase solid solution of Co in Ni with slightly different compositions and very similar diffraction patterns as shown in the Figs. 11 and 12. Thus, solid solution of chemical components (metals) remain in a single homogeneous phase in all proportions of constituents [37].
The average grain size of MED Ni-Co alloy coatings deposited under parallel and perpendicular conditions of B, calculated using Eq. (1) and it was found to be in the range of 26 nm and 20 nm, respectively. The grain size of the normal electrodeposited coatings was reduced on the application of magnetic field in particular perpendicular direction of B, which accelerates the rate of reaction and improves the nucleation and mass transfer process [35]. Hence, improved corrosion resistance of MED alloy coatings was observed under the influence of perpendicular B [38]. The finer grains were produced under the effect of magnetic field as compared to normal electrodeposited alloys. Further, refinement in grain size of MED coatings was confirmed by the increased charge transfer resistance of EIS curves. Basically, MED coatings blocks the active growth sites for corrosion and decreases the activation energy for nucleation [39].

Compositional Analysis
The EDX analysis of magnetoelectrodeposited coatings was given in the Table 3. From the data, it was observed that the content of cobalt increases with increase of magnetic field intensities upto 0.3 T. This is attributed to the fact the under the influence of magnetic field cobalt is more magnetically active than Nickel. Hence, cobalt content got increased gradually with increase of field intensities. At B = 0.4 T cobalt content again got decreased,  4 since under the influence of magnetic field the wt% of Co content reached a optimum value at B = 0.3 T i.e. limiting value, Beyond that coating was not found to be stable. The wt% of Cobalt coatings obtained in perpendicular direction (B) was found to be high. This is due to the fact that Lorentz force is more pronounced in perpendicular direction magnetic field than that of magnetic field in parallel direction. From the Table 3, it was clear that the presence of magnetic field in perpendicular and parallel direction limits the contents of both Nickel and cobalt in the coatings to produce better corrosion resistant coatings. From the literature, it was observed that the content of cobalt plays an important role to increase the corrosion resistance of Ni-Co alloy. The content of cobalt is feasible in the range of 11-20% [27,29,34]. This could be achieved with the help of magnetic field effect. The induced magnetic field intensity 0.3 T in a perpendicular direction restricts the amount of cobalt to 20%. Hence, magnetoelectrodeposition technique sets a particular wt% value for Ni and Co in the coatings to produce more corrosion resistant materials.

SEM Study
The surface morphology of MED Ni-Co alloy coatings, developed under different conditions of B have been examined under SEM, and are shown in Figs. 13 and 14. A clear difference in microstructure of MED alloy coatings was observed with change of intensity of B from 0.1 to 0.4 T, in both parallel and perpendicular B and corresponding SEM images are as shown in Figs. 13a-d and 14a-d. The morphology of the coating was inferred that with increase of field intensities the surface smoothness of the coating also increases, in other words nodular size of the coatings decreases and it provides more nucleation site, which was leading to more compact structure [40].
The effect of magnetic field is more pronounced in case of perpendicular direction as compared to parallel direction. The surface smoothness, increases when the magnetic field oriented in perpendicular direction. Since the Lorentz force acting maximal in perpendicular direction of B on the surface of base materials. Hence, MED (Ni-Co) 4.0/0.3 T/Per coating surface was found to be smoother, uniform and crack free, compared all other deposited coatings. The surface roughness of (Ni-Co) 4.0/0.4 T/Per or (Ni-Co) 4.0/0.4 T/Par coatings were relatively higher with increase of grain size, which was attributed to increase of hydrogen evolution reaction at higher magnetic field intensity. The excess evolution of hydrogen gas at higher field intensity B = 0.4 T was indicated by the formation of bubbles on the surface of coatings and alternatively increases the surface roughness of the coating [41]. The surface morphology of ED Ni-Co alloy coatings (optimal) in comparison with MED Ni-Co alloy coatings, under optimal conditions of both parallel and perpendicular B is as shown in Fig. 15a-c. It may be noted that ED Ni-Co alloy coatings, where B = 0 T exhibits a rough surface, compare to MED Ni-Co alloy coatings, under both parallel and perpendicular conditions. This may be attributed to the excessive evolution of hydrogen during conventional codeposition process [42].
When B is oriented perpendicular to the electrode surface, maximum magneto convection effect was observed on the surface of the cathode. As a result, change in surface morphology of the coating was observed tremendously in a perpendicular direction magnetic field. The Lorentz force was responsible for increase in mass transfer process towards cathode [43]. This in turn decreases the thickness of diffusion layer towards electrode [44]. Hence, the surface has become flat in the case of perpendicular direction coating as compared to parallel direction and conventional coatings. Hence, this effect smoothens the surface of the coatings and increases the corrosion performance of the coatings. On comparing Fig. 15a-c, it was clear that nodular size has decreased with the application of magnetic field, this is beneficial to obtain uniform dense structure. As a result, it is very difficult for corrosive media to enter into dense structure to cause corrosion mechanism. Hence, corrosion resistant of the coating increases (Jiang et al.) [40].

AFM Study
The surface roughness of alloy coatings were studied using three-dimensional Atomic Force Microscopy (AFM) techniques. The AFM image of Ni-Co alloy coatings, corresponding to three optimal conditions, i.e. ED (Ni-Co) 4 The ED (Ni-Co) 4.0 Adm −2 coating exhibits nodular like protrusion structure with higher average surface roughness (R a ) values. The surface roughness of the alloy coatings has reduced substantially, with the induced magnetic field B in parallel and perpendicular direction. The AFM study revealed that the average roughness of alloy coatings corresponding to (Ni-Co) 4 Table 5. From the data, it was clear that (Ni-Co) 4.0/0.3 T/per and (Ni-Co) 4.0/0.3 T/par coatings posses lower R a values as compared to (Ni-Co) 4.0 Adm −2 coating and results revealed that applied magnetic field facilitated the decrease of roughness values and suitable condition of magnetic field (0.3 T, in perpendicular direction) increases the smoothness of the coatings and hence, corrosion performance of the coatings.
On comparing Fig. 16a-c, coatings developed under the influence of magnetic field exhibited relatively smaller granular structure, which alternatively enhances the corrosion resistant behaviour of the developed coatings.

Discussion
The MED approach was adopted to improve corrosion resistance property of normal electrodeposited Ni-Co alloy coating. The factor responsible for improved corrosion resistance of MED Ni-Co alloy coatings is limited to wt% of cobalt and nickel. According to simple diffusion theory, under the influence of magnetic field, change in composition of the coatings was observed and is directly proportional to concentration change of the ions near the diffusion layer of cathode and schematic representation is as shown in Fig. 17.
The relationship between limiting current density of ions and diffusion layer thickness is given in Eq. (2).
where n is the valency of the metal ions and F is the Faraday constant (96,400 C), D is the diffusion coefficient of the reacting species, C B is the concentration and δ is the thickness of electrical double layer (EDL).
Under normal electrodeposition process, it was found that coating with 78.2 wt% of Ni and 21.80% of Co was found to be more corrosion resistant with corrosion current density value 20 µA cm −2 . In the presence of magnetic field, minimum corrosion current density (2 µA cm −2 ) was observed for (Ni-Co) 4.0/0.3 T/per coating with 79.51 wt% of Ni and 20.49 wt% of Co. Hence, drastic decrease in corrosion current density was observed in the presence of applied magnetic field.
The (Ni-Co) 4.0/0.3 T/per coating obtained in a perpendicular direction magnetic field was found to be more corrosion resistant as compared other coating configurations. This may be attributed to the combined effect of Lorentz force and non-electrostatic force acting on ions during deposition in the presence of magnetic field. The Lorentz force is maximal when field is applied perpendicular to the direction of flow of ions, which is responsible for macro-MHD to decrease the thickness of diffusion layer near to the electrode. It may be noted that thickness of diffusion layer decreased from δ 0 to δ D , as the mode of the coating is changed from ED to MED type. Further, an increase of i L for deposition of Co, due to induced of magnetic field is shown schematically in Fig. 17, supported by the Eq. (2). The coating with Co content to a particular value 20.49 wt% was found to be more corrosion resistant, due to increase of its limiting current (i L) and this effect was responsible for decreased corrosion rates of Ni-Co alloy  Table 5 The surface roughness data of ED (Ni-Co) 4 coatings [45]. Further increase of B = 0.4 T, both parallel and perpendicular causes diminish in the mass transport of cobalt ions and increases the evolution of hydrogen bubbles at the cathode. Hence, increase in corrosion rate was observed. Under the influence of magnetic field, the presence of cobalt prevents the formation of holes during hydrogen evolution reaction. Hence, at lower magnetic field intensities improvement in corrosion resistant behaviour of the material was observed.

Conclusions
In an effort to optimise a sulphate bath of Ni-Co alloy, and to improve its corrosion resistance behaviour using the benefit of magnetic field, applied parallel to the process of normal electrodeposition and following conclusions are drawn: 1. Under normal electrodeposition (Ni-Co) 4.0A dm −2 was found to be more corrosion resistant. This is attributed to change of electrodeposition from anomalous to normal type. 2. The corrosion performance of Ni-Co alloy coatings has been improved with advent of magnetoelectrodeposition (MED) by inducing the magnetic field B in parallel and perpendicular to the flow of ions. 3. The modulation in mass transfer has been observed in the presence of applied magnetic field and it improved the corrosion resistant behaviour of Ni-Co alloy. 4. Under optimal conditions, MED coatings exhibits eleven-time better corrosion resistance compared to conventionally electrodeposited (ED) coatings, using same bath, deposited for same time. 5. The roughness of Ni-Co alloy coatings was found to be decreased under magnetoelectrodeposition process, supported by SEM and AFM analyses. 6. The improved corrosion resistance of MED Ni-Co alloy coatings in a perpendicular direction magnetic field was attributed to maximal action of Lorentz force on movement of ions towards cathode. And results were supported by supported by EDX, XRD, SEM and AFM study.