TECHNICAL FIELD
The present disclosure relates to the field of electroplating. Particularly, the present disclosure
relates to electroplating compositions to provide pure zinc (Zn) coatings, methods of preparing
them, direct and pulsed current methods of depositing these electroplating compositions on
steel substrates and steel substrates obtained therefrom.
BACKGROUND OF THE DISCLOSURE
Zinc coatings have extensively been used for improving the corrosion resistance of steel. Zinc
is well known for imparting sacrificial corrosion resistance to steel, along with the benefit of a
low cost. Hot dip galvanised steel is the most popular coated steel product used in automotive
segment. However, hot-dip galvanising has certain disadvantages like poor coating thickness
control, and impossibility of single sided coatings. Another problem with the hot-dipping of
zinc for high strength alloy steels is that they suffer from selective oxidation of alloying
elements in the steel during annealing, resulting in poor wettability of molten zinc.
One of the ways by which these problems can be addressed is by electrodeposition of zinc
(electrogalvanising) instead of hot-dipping. Electrogalvanising offers many advantages in
comparison to hot-dipping, like coating at room temperature, production of more compact
coatings, better control over coating thickness, and the possibility of one-sided coating.
However, there is a lot of scope to introduce special functionalities in the coating as demanded
by the automotive segments. At present, functionalities like self-passivation and self-
lubrication are achieved through an additional inorganic or organic coating over and above the
zinc metallic coating.
The present disclosure aims to provide a comprehensive coating solution where the
multifunctional requirements of the automotive industry can be achieved through a single
coating system. Further, the present disclosure aims to provide Zn coatings with corrosion
resistance properties similar to the conventional galvanised steel at a reduced coating thickness
along with a refinement in the morphologies.

STATEMENT OF THE DISCLOSURE
The present disclosure relates to an electroplating composition comprising zinc sulphate, zinc
chloride, and boric acid, wherein the electroplating composition has a pH of about 3-4.5. In
some embodiments, the electroplating compositions comprise additives selected from cetyl
trimethyl ammonium bromide (CTAB), benzylidene acetone, or a combination thereof.
The present disclosure also relates to a method for preparing the electroplating composition
described herein, comprising: a) heating water to about 50-60℃ to obtain a heated water; b)
adding boric acid to the heated water to obtain a first solution; c) adding zinc sulphate to the
first solution to obtain a second solution; d) adding zinc chloride to the second solution to
obtain a third solution; and e) adjusting pH of the third solution to provide the electroplating
composition. When the electroplating composition comprises an additive, the additive is added
to the first solution prior to adding zinc sulphate.
The present disclosure provides direct current and pulsed current methods for depositing the
electroplating compositions. The direct current method for depositing the electroplating
composition on a steel substrate, comprises: a) providing the steel substrate as a cathode; and
b) depositing the electroplating composition on the steel substrate at a constant current with a
current density of about 170-190 mA/cm2 and at a stirring rate of about 250-350 rpm to provide
a steel substrate comprising a Zn coating.
The pulsed current method for depositing the electroplating composition on a steel substrate,
comprises: a) providing the steel substrate as a cathode; and b) depositing the electroplating
composition on the steel substrate by employing a pulsed current with an average current
density of about 170-190 mA/cm2, a peak current density of about 240-720 mA/cm2, a duty
cycle of about 25-75%, and a frequency of about 25-200 Hz; wherein the electroplating
composition is stirred at a rate of about 250-350 rpm during said depositing to provide a steel
substrate comprising a zinc (Zn) coating
The present disclosure further relates to steel substrate comprising Zn coatings, wherein the Zn
coatings show a uniform morphology and fine grain structure and have superior corrosion
resistance.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1 shows the schematic of an exemplary method of preparing the electroplating
composition.
Figure 2 shows morphologies of the Zn coatings deposited using the direct current method at
varying current densities.
Figure 3 shows morphologies of the Zn coatings deposited using the pulsed current method at
different duty cycles and frequencies.
Figure 4 shows the combined effect of unique pulsed current deposition parameters along with
the best additive concentration to control the morphology at a max to achieve the best corrosion
properties.
Figure 5 shows the morphology and the corrosion current of the Zn coatings of the present
disclosure and those of the benchmark (commercial) coating.
Figure 6 shows the morphology, cross-section of the coating (throughout uniformity),
deposition kinetics, corrosion current and corrosion potential.
DETAILED DESCRIPTION OF THE DISCLOSURE
With respect to the use of substantially any plural and/or singular terms herein, those having
skill in the art can translate from the plural to the singular and/or from the singular to the plural
as is appropriate to the context and/or application. The various singular/plural permutations
may be expressly set forth herein for sake of clarity. The use of the expression “at least” or “at
least one” suggests the use of one or more elements or ingredients or quantities, as the use may
be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Throughout this specification, the word “comprise”, or variations such as “comprises” or
“comprising” or “containing” or “has” or “having”, or “including but not limited to” wherever
used, will be understood to imply the inclusion of a stated element, integer or step, or group of
elements, integers or steps, but not the exclusion of any other element, integer or step, or group
of elements, integers or steps.

Reference throughout this specification to “some embodiments”, “one embodiment” or “an
embodiment” means that a particular feature, structure or characteristic described in connection
with the embodiment may be included in at least one embodiment of the present disclosure.
Thus, the appearances of the phrases “in some embodiments”, “in one embodiment” or “in an
embodiment” in various places throughout this specification may not necessarily all refer to
the same embodiment. It is appreciated that certain features of the disclosure, which are, for
clarity, described in the context of separate embodiments, may also be provided in combination
in a single embodiment. Conversely, various features of the disclosure, which are, for brevity,
described in the context of a single embodiment, may also be provided separately or in any
suitable sub-combination.
As used herein, the term “electroplating composition” refers to an electroplating bath
comprising electrolytes (Zn salts) and optionally additives.
The term “about” as used herein encompasses variations of +/-5% and more preferably +/-
2.5%, as such variations are appropriate for practicing the present invention.
The present disclosure provides electroplating compositions for depositing Zn coatings on steel
substrates. These compositions broadly fall into two categories: compositions without additives
and compositions with additives. Further, the present disclosure provides two different
methods for depositing/electroplating these compositions on steel substrates: a direct current
(DC) method and a pulsed current method.
In some embodiments, the present disclosure provides an electroplating composition
comprising zinc sulphate, zinc chloride, and boric acid, wherein the electroplating composition
has a pH of about 3-4.5. In some embodiments, the electroplating composition comprises zinc
sulphate in an amount of about 200-300 g/L, zinc chloride in an amount of about 5-8 g/L, and
boric acid in an amount of about 22-35 g/L. In some embodiments, the electroplating
composition comprises zinc sulphate in an amount of about 250 g/L, zinc chloride in an amount
of about 5-8 g/L, and boric acid in an amount of about 22-35 g/L. In an exemplary embodiment,
the electroplating composition comprises zinc sulphate in an amount of about 250 g/L, zinc
chloride in an amount of about 6 g/L, and boric acid in an amount of about 30 g/L.

Table 1A: Electroplating Composition without additives
Constituent Concentration (g/L) Exemplary Embodiment
Concentration (g/L)
Zinc sulphate 200-300 250
Zinc chloride 5-8 6
Boric acid 22-35 30
Table 1A: Electroplating Composition without additives
Constituent I Concentration (g/L) I Exemplary Embodiment
Concentration (g/L)
Zinc sulphate 200-300 ~250
Zinc chloride 5-8 ~6
Boric acid ~22-35 "30
The inventors found that concentrations lower than 200 g/L of zinc sulphate caused burnt
deposits at the edges, particularly at high current density. On the other hand, although higher
concentrations of zinc sulphate provided higher deposition kinetics, the corrosion properties of
the Zn coatings were found to be better at lower concentration of the salts. The inventors found
that zinc sulphate in the amount of about 200-300 g/L provides Zn coatings with desired
morphology and corrosion properties.
In some embodiments, the electroplating composition further comprises an additive selected
from cetyl trimethyl ammonium bromide (CTAB), benzylidene acetone, or a combination
thereof. Accordingly, in some embodiments, the electroplating composition comprises zinc
sulphate, zinc chloride, boric acid, and an additive selected from CTAB, benzylidene acetone,
or a combination thereof wherein the electroplating composition has a pH of about 3-4.5.
In some embodiments, the electroplating composition comprises about 200-300 g/L zinc
sulphate, about 5-8 g/L zinc chloride, about 22-35 g/L boric acid, about 0.5-2.5 g/L CTAB,
and/or about 0.05-0.2 g/L benzylidene acetone.
In some embodiments, the electroplating composition comprises about 250 g/L zinc sulphate,
about 5-8 g/L zinc chloride, about 22-35 g/L boric acid, about 0.5-2.5 g/L CTAB, and/or about
0.05-0.2 g/L benzylidene acetone.
In some embodiments, the electroplating composition comprises about 250 g/L zinc sulphate,
about 6 g/L zinc chloride, about 30 g/L boric acid, about 0.5-2.5 g/L CTAB, and/or about 0.05-
0.2 g/L benzylidene acetone.

In some embodiments, the electroplating composition comprises about 250 g/L zinc sulphate,
about 5-8 g/L zinc chloride, about 22-35 g/L of boric acid, and about 2 g/L CTAB and/or about
0.15 g/L benzylidene acetone. This is shown in Table 1B.
Table 1B: Electroplating Composition with additives
Constituent I Concentration (g/L) I Exemplary Embodiment
Concentration (g/L)
Zinc sulphate 200-300 "250
Zinc chloride 5-8 6
Boric acid 22-35 30
CTAB or benzylidene 2 g/L CTAB and/or 0.15 g/L 2 g/L CTAB and/or 0.15
acetone benzylidene acetone g/L benzylidene acetone
In some embodiments, the electroplating composition comprises about 250 g/L zinc sulphate,
about 5-8 g/L zinc chloride, about 22-35 g/L of boric acid, and about 1 g/L CTAB and/or about
0.07 g/L benzylidene acetone. This is shown in Table 1C.
Table 1C: Electroplating Composition with additives
Constituent I Concentration (g/L) I Exemplary Embodiment
Concentration (g/L)
Zinc sulphate 200-300 "250
Zinc chloride 8 6
Boric acid 22-35 30
CTAB or benzylidene 1 g/L CTAB and/or 0.07 g/L 1 g/L CTAB and/or 0.07
acetone benzylidene acetone g/L benzylidene acetone
The inventors have found that the compositions shown in Tables 1A, 1B, and 1C when
deposited in the manner described herein provide Zn coatings with the highest corrosion
resistance. Further, these compositions show high deposition kinetics.
In some embodiments, zinc sulphate is present in the electroplating composition in an amount
of about 200-300 g/L, including values and ranges thereof. For example, in some embodiments,
zinc sulphate is present in the electroplating composition in an amount of about 200, 205, 210,
215, 220, 225, 230, 235, 240, 245, 250, 255, 260, 265, 270, 275, 280, 285, 290, 295, or 300
g/L, including values and ranges thereof. In some embodiments, zinc sulphate is present in the

electroplating composition in an amount of about 230-270, 235-265, 240-260, or 245-255 g/L,
including values and ranges thereof. In some embodiments, zinc sulphate is present in the
electroplating composition in an amount of about 250 g/L. In some embodiments, zinc sulphate
is ZnSO4.xH2O where x is 0 to 7. In an exemplary embodiment, the electroplating composition
comprises the heptahydrate form of zinc sulphate (ZnSO4.7H2O).
In some embodiments, zinc chloride is present in the electroplating composition in an amount
of about 5-8 g/L, including values and ranges thereof. For example, in some embodiments, zinc
chloride is present in the electroplating composition in an amount of about 5, 5.5, 6, 6.5, 7, 7.5,
or 8 g/L, including values and ranges thereof. In some embodiments, zinc chloride is present
in the electroplating composition in an amount of about 5.5-6.5 g/L. In some embodiments,
zinc chloride is present in the electroplating composition in an amount of about 6 g/L.
In some embodiments, boric acid is present in the electroplating composition in an amount of
about 22-35 g/L, including values and ranges thereof. For example, in some embodiments,
boric acid is present in the electroplating composition in an amount of about 22-34, 22-30, 24-
32, 24-30, 25-32, 25-30, 26-35, 26-32, 26-30, 27-35, 27-33, 27-31, 27-30, 28-33, 28-32, or 29-
31 g/L, including values and ranges thereof. In some embodiments, boric acid is present in the
electroplating composition in an amount of about 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33,
34, or 35 g/L.
In some embodiments, CTAB is present in the electroplating composition in an amount of
about 0.5-2.5 g/L, including values and ranges thereof. In some embodiments, CTAB is present
in the electroplating composition in an amount of about 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, or
2.5 g/L. In exemplary embodiments, CTAB is present in the electroplating composition in an
amount of about 1 g/L or 2 g/L.
In some embodiments, benzylidene acetone is present in the electroplating composition in an
amount of about 0.05-0.2 g/L, including values and ranges thereof. In some embodiments,
benzylidene acetone is present in the electroplating composition in an amount of about 0.05,
0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, or 0.2 g/L. In
exemplary embodiments, benzylidene acetone is present in the electroplating composition in
an amount of about 0.15 g/L or 0.07 g/L.

In some embodiments, a combination of CTAB and benzylidene acetone is present in the
composition in the amounts described herein.
One of ordinary skill in the art would understand that any combination of the individual
amounts of zinc sulphate, zinc chloride, boric acid, and optionally CTAB or benzylidene
acetone disclosed herein is contemplated by the present disclosure.
The electroplating compositions of the present disclosure have a pH of about 3-4.5 such as the
pH of about 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, or 4.5. In some
embodiments, the pH of the electroplating composition is about 3.2-4.5, 3.2-4.3, 3.2-4.2, 3.2-
4.1, 3.2-3.8, 3.5-4.5, 3.5-4.4, 3.5-4.3, 3.5-4.2, 3.5-4.1, 3.7-4.5, 3.7-4.3, 3.7-4.2, 3.8-4.5, 3.8-
4.4, 3.8-4.3, 3.8-4.2, 3.9-4.5, 3.9-4.4, 3.9-4.3, 3.9-4.2, 4-4.5, 4-4.4, or 4-4.3, including values
and ranges thereof. In an exemplary embodiment, the pH of the electroplating composition is
about 3.5.
The present disclosure also provides methods for preparing the electroplating compositions
described herein. In some embodiments, the method for preparing the electroplating
composition without additives comprises: a) heating water to about 50-60 ͦ C to obtain heated
water; b) adding boric acid to the heated water to obtain a first solution; c) adding zinc
sulphate to the first solution to obtain a second solution; d) adding zinc chloride to the second
solution to obtain a third solution; and e) adjusting pH of the third solution to provide the
electroplating composition. Heating to about 50-60℃ is continued during the addition of boric
acid, zinc sulphate and zinc chloride. The heated water and the solutions are stirred
continuously throughout the preparation of the composition at a rate of about 250-350 rpm. In
some embodiments, the stirring rate is about 300 rpm.
In some embodiments, the method for preparing the electroplating composition with additives
comprises: a) heating water to about 60-70 ͦ C to obtain heated water; b) adding boric acid to
the heated water to obtain a first solution; c) adding CTAB and/or benzylidene acetone to the
first solution to obtain a second solution; d) adding zinc sulphate to the second solution to
obtain a third solution; e) adding zinc chloride to the third solution to obtain a fourth solution;
and f) adjusting pH of the fourth solution to provide the electroplating composition. Heating to
about 50-60 ͦ C is continued during the addition of boric acid, CTAB and/or benzylidene
acetone, zinc sulphate and zinc chloride. The heated water and the solutions are stirred

continuously throughout the preparation of the composition at a rate of about 250-350 rpm. In
some embodiments, the stirring rate is about 300 rpm. An exemplary schematic of the process
is shown in FIG. 1.
The pH of the electroplating composition is adjusted to about 3-4.5. In an exemplary
embodiment, the pH of the electroplating composition is adjusted to about 3.5. In some
embodiments, the pH of the electroplating composition is adjusted using sulphuric acid and/or
sodium hydroxide.
The present disclosure also provides methods for depositing the electroplating compositions
described herein on a steel substrate to provide steel substrates comprising Zn coatings. In some
embodiments, the electroplating compositions are deposited using a direct current (DC)
method. In some embodiments, the electroplating compositions are deposited using a pulsed
current method.
Direct Current (DC) Deposition
In some embodiments, the method for depositing the electroplating composition on a steel
substrate comprises: a) providing the steel substrate as a cathode; and b) depositing the
electroplating composition on the steel substrate at a constant current with a current density of
about 170-190 mA/cm2 and at a stirring rate of about 250-350 rpm to provide a steel substrate
comprising a Zn coating. Exemplary parameters for depositing the electroplating composition
are shown in Table 2.
Table 2: Exemplary parameters for DC deposition of a Zn coating
Electroplating parameter pValue
Current density of deposition 170-190 mA/cm2
Stirring rate of deposition 250-350 rpm 25
In some embodiments, the compositions shown in Tables 1A and 1B are deposited by the DC
method.
The inventors have found that at a zinc sulphate concentration of about 200-300 g/L and at a
current density of about 170-190 mA/cm2, Zn coatings with a uniform and fine morphology
are obtained. FIG. 2 shows a comparison of the morphologies (grain structure) of the Zn

coatings obtained at 250 g/L of zinc sulphate and at current densities of 50, 150, and 250
mA/cm2.
In some embodiments, the current density employed in the DC method of deposition is about
170, 175, 180, 185, or 190 mA/cm2, including values and ranges thereof. In some embodiments,
the current density employed in the DC method of deposition is about 175-185 mA/cm2,
including values and ranges thereof. In an exemplary embodiment, the current density for the
DC deposition is about 180 mA/cm2.
Unlike prior studies on Zn electrodeposition, the present disclosure has explored the effect of
stirring the electroplating composition during the process of deposition. The inventors observed
that the stirring rate affects the Zn content, the morphology, and the corrosion rate of the
deposit. In some embodiments, the stirring rate of the electroplating composition in the method
of depositing ranges from about 250-350 rpm, 275-325 rpm, 280-320 rpm, or about 290-310
rpm, including values and ranges thereof. In some embodiments, the stirring rate of the
electroplating composition is about 300 rpm.
In some embodiments, the DC method for depositing the electroplating composition is carried
out for about 5-8 minutes such as for about 5, 6, 7, or 8 minutes. In an exemplary embodiment,
the DC method is carried out for about 5 minutes.
In some embodiments, the Zn coatings provided by the DC method of depositing the
electroplating composition exhibit a corrosion current density (Icorr) of about 1.2-1.6 μA/cm2,
including values and ranges thereof. In some embodiments, the Zn coatings obtained by the
DC method exhibit a corrosion current density of about 1.2, 1.3, 1.4, 1.5, or 1.6 μA/cm2. In
some embodiments, the composition without additives (e.g., compositions shown in Table 1A)
deposited by employing the DC method provides the corrosion current in the range of about
5.4-6 µA/cm2. The inventors found that the addition of an additive (CTAB and/or benzylidene
acetone) to this composition lowers the corrosion current values substantially. For example,
upon addition of CTAB and/or benzylidene acetone, the corrosion current is lowered to about
1.2-1.5 µA/cm2.
In some embodiments, the Zn coatings provided by the DC method of depositing the
electroplating composition exhibit a corrosion potential (Ecorr) of about -1.08 to -1.20 V,

including values and ranges thereof. In some embodiments, the Zn coatings obtained by the
DC method exhibit a corrosion potential of about -1.08, -1.09, -1.1, or -1.2 V.
In some embodiments, the DC method for depositing the electroplating composition provides
a deposition rate of about 0.8-4 µm/min, including values and ranges thereof. In some
embodiments, the DC method provides a deposition rate of about 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4,
1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6,
3.7, 3.8, 3.9, or 4 µm/min. In exemplary embodiments, the DC method provides a deposition
rate of about 3.7 µm/min.
In an exemplary embodiment, a set up for depositing the electroplating composition on a steel
substrate comprises placing the steel substrate as a cathode and a pure zinc plate as an anode
in the electroplating composition, stirring the electroplating composition, and passing a direct
current between these two electrodes.
Pulsed Current Deposition
In some embodiments, the method for depositing the electroplating composition on a steel
substrate comprises: a) providing the steel substrate as a cathode; and b) depositing the
electroplating composition on the steel substrate by employing a pulsed current with an average
current density of about 170-190 mA/cm2, a peak current density of about 240-720 mA/cm2, a
duty cycle of about 25-75%, and a frequency of about 25-200 Hz; wherein the electroplating
composition is stirred at a rate of about 250-350 rpm during said depositing to provide a steel
substrate comprising a Zn coating.
Exemplary parameters for depositing the electroplating composition are shown in Table 3.

Table 3: Exemplary parameters for pulsed current deposition of a Zn coating
Electroplating parameter Value
Average current density of deposition 170-190 mA/cm2
Peak current density 240-720 mA/cm2
Duty cycle 25-75% 30
Frequency 25-200 Hz
Stirring rate of deposition 250-350 rpm

In some embodiments, the compositions shown in Tables 1A and 1C are deposited by the
pulsed current method.
The inventors found that zinc sulphate concentrations higher than 300 g/L did not provide good
corrosion resistance to Zn coatings. On the other hand, at zinc sulphate concentration of about
200-300 g/L and an average current density of about 170-190 mA/cm2, Zn coatings with a
uniform and fine morphology (grain structure) are obtained. The more uniform the grain
structure, the better is the corrosion resistance.
Further, in the pulsed method, the duty cycle and the frequency of the pulsed current also
affected the morphology of the coating. A uniform and fine grain structure of the Zn coating is
obtained with moderate duty cycle (50%) with high frequency (200 Hz) and high duty cycle
(75%) with low frequency (25Hz). The coatings obtained using these duty cycles and
frequencies provide very low corrosion currents. For example, the coating deposited by a
pulsed current at 50% duty cycle and 200 Hz frequency showed a corrosion current of 1.64
μA/cm2 and the coating deposited by a pulsed current at 75% duty cycle and 25 Hz frequency
showed a corrosion current of 1.58 μA/cm2.
FIG. 3 shows a comparison of the morphologies (grain structure) of the Zn coatings obtained
at different duty cycles and frequencies.
The inventors found that the addition of CTAB or benzylidene acetone also improved the grain
structure of the Zn coating. FIG. 4 shows the effect of addition of CTAB and benzylidene
acetone to the electroplating composition on the morphology of the Zn deposits. In some
embodiments, exemplary compositions comprising additives shown in Table 1C are employed
in the pulsed current method.
Although the addition of CTAB or benzylidene acetone improved the grain structure of the Zn
coating, it is noted that the composition without these additives such as those shown in Table
1A also provided satisfactory corrosion resistance when deposited using the DC or pulsed
method. One would understand that the addition of CTAB or benzylidene acetone to the
electroplating composition would increase the overall cost of the deposition; therefore, in some
embodiments, to keep the costs in control, it is desirable to employ the compositions in Table
1A as these compositions provide satisfactory corrosion resistance.

In some embodiments, the average current density employed in the pulsed method of
deposition is about 170, 175, 180, 185, or 190 mA/cm2, including values and ranges thereof.
In some embodiments, the average current density employed in the pulsed method of
deposition is about 175-185 mA/cm2, including values and ranges thereof. In an exemplary
embodiment, the average current density for the pulsed deposition is about 180 mA/cm2.
In some embodiments, the peak current density employed in the pulsed method of deposition
is about 240-720, including values and ranges thereof. In some embodiments, the peak current
density in the pulsed method of deposition is about 240-680, 240-640, 240-600, 240-580, 240-
540, 240-500, 240-460, 240-420, 240-360, 240-320, 280-720, 280-680, 280-640, 280-600,
280-580, 280-540, 280-500, 280-460, 280-420, 280-360, 320-720, 320-680, 320-640, 320-600,
320-580, 320-540, 320-500, 320-460, 320-420, 320-360, 360-720, 360-680, 360-640, 360-600,
360-580, 360-540, 360-500, 360-460, 360-420, 400-720, 400-680, 400-640, 400-600, 400-580,
400-540, 400-500, 400-460, 400-420, 440-720, 440-680, 440-640, 440-600, 440-580, 440-540,
440-500, 480-720, 480-680, 480-640, 480-600, 480-580, 480-540, 520-720, 520-680, 520-640,
520-600, 520-580, 560-720, 560-680, 560-640, 560-600, 600-720, 600-680, 600-640, 640-720,
640-680, or 680-720 mA/cm2, including values and ranges thereof. In an exemplary
embodiment, the peak current density for the pulsed deposition is about 240, 250, 260, 270,
280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460,
470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 610, 620, 630, 640, 650,
660, 670, 680, 690, 700, 710, or 720 mA/cm2.
In some embodiments, the duty cycle of the pulsed current varies from about 25-75%, such as
about 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or 75%. In an exemplary
embodiment, the duty cycle is about 25%, 50%, or 75%.
In some embodiments, the frequency of the pulsed current is about 25-200 Hz, such as about
25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135,
140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, or 200 Hz. In some embodiments,
the frequency is about 25, 50, 75, 100, 125, 150, 175, or 200 Hz. In some embodiments, the
pulsed current has a duty cycle of about 15%, 25%, or 50% and the frequency of about 175-
200 Hz. In some embodiments, the pulsed current has a duty cycle of about 65%, 70%, or 75%
and the frequency of about 25-50 Hz. In some embodiments, the pulsed current has a duty cycle

of about 50% and the frequency of about 200 Hz. In some embodiments, the pulsed current has
a duty cycle of about 75% and the frequency of about 25 Hz. The effect of the duty cycle and
the frequency of the pulsed current on the morphology of the Zn coatings is shown in FIG. 3.
In some embodiments, the pulsed current has ton of about 25-35 ms and toff of about 5-15 ms,
including values and ranges thereof. In an exemplary embodiment, the pulsed current has ton
of about 30 ms and toff of about 10 ms.
Stirring the electroplating composition during deposition was found to affect the Zn content,
the morphology, and the corrosion rate of the deposit. In some embodiments, the stirring rate
of the electroplating composition in the pulsed method of depositing ranges from about 250-
350 rpm, 275-325 rpm, 280-320 rpm, or about 290-310 rpm, including values and ranges
thereof. In some embodiments, the stirring rate during deposition is about 300 rpm.
In an exemplary embodiment, the electroplating composition of Table 1A and 1C is deposited
on a steel substrate by employing the pulsed current having an average current density of about
180 mA/cm2, a peak current density of about 240 mA/cm2, a duty cycle of about 75%, a
frequency of about 25 Hz, and at a stirring rate of about 300 rpm.
In some embodiments, the pulsed method for depositing the electroplating composition is
carried out for about 5-8 minutes such as for about 5, 6, 7, or 8 minutes. In an exemplary
embodiment, the pulsed method is carried out for about 5 minutes.
In some embodiments, the Zn coatings provided by the pulsed method of depositing the
electroplating composition exhibit a corrosion current density (Icorr) of about 1.0-1.7 μA/cm2,
including values and ranges thereof. In some embodiments, the Zn coatings obtained by the
pulsed method exhibit a corrosion current density of about 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, or
1.7 μA/cm2. In some embodiments, the Zn coatings obtained by the pulsed method exhibit a
corrosion current density of about 1.2-1.6 μA/cm2.
In some embodiments, the Zn coatings provided by the pulsed method of depositing the
electroplating composition exhibit a corrosion potential (Ecorr) of about -1.08 to -1.15 V,
including values and ranges thereof. In some embodiments, the Zn coatings obtained by the

pulsed method exhibit a corrosion potential of about -1.08, -1.09, -1.1, -1.11, -1.12, -1.13, -
1.14, or -1.15 V.
In some embodiments, the pulsed method for depositing the electroplating composition
provides a deposition rate of about 1.5-3 µm/min, including values and ranges thereof. In some
embodiments, the pulsed method provides a deposition rate of about 1.5, 1.6, 1.7, 1.8, 1.9, 2,
2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3 µm/min. In exemplary embodiments, the pulsed
method provides a deposition rate of about 1.7-2.8 µm/min.
In an exemplary embodiment, a set up for depositing the electroplating composition on a steel
substrate comprises placing the steel substrate as a cathode and a pure zinc plate as an anode
in the electroplating composition, stirring the electroplating composition, and passing the
pulsed current between these two electrodes.
The present disclosure also provides steel substrates comprising Zn coatings. In some
embodiments, the thickness of the Zn coatings is reduced compared to conventional Zn
coatings; at the same time, the corrosion resistance and the microstructure (i.e.,
morphology/grain structure) of the Zn coating is improved compared to conventional Zn
coatings. In some embodiments, the present disclosure provides steel substrates comprising Zn
coatings where the thickness of the Zn coatings is reduced by about 10%, 15%, 20%, 25%,
30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or 75% compared to conventional Zn
coatings.
In some embodiments, provided herein are steel substrates comprising Zn coatings, wherein
the coating exhibits uniform morphology. In some embodiments, the Zn coatings exhibit
uniform, fine, and compact morphology.
In some embodiments, provided herein are steel substrates comprising Zn coatings, wherein
the coatings exhibit a corrosion current density (Icorr) of about 1.0-1.7 μA/cm2, including values
and ranges thereof. In some embodiments, the steel substrates comprise Zn coatings that exhibit
a corrosion current density of about 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, or 1.7 μA/cm2. In some
embodiments, the steel substrates comprise Zn coatings that exhibit a corrosion current density
of about 1.2-1.6 μA/cm2.

In some embodiments, provided herein are steel substrates comprising Zn coatings, wherein
the coatings exhibit a corrosion potential (Ecorr) of about -1.08 to -1.20 V, including values and
ranges thereof. In some embodiments, the steel substrates comprise Zn coatings that exhibit a
corrosion potential of about 1.08, -1.09, -1.1, -1.11, -1.12, -1.13, -1.14, -1.15 V, -1.17, -1.18, -
1.19, or -1.2 V.
The electroplating compositions, methods of producing them, methods of depositing them on
a steel substrate and steel substrates comprising Zn coatings disclosed herein provide many
advantages. First, while there have been many attempts to develop Zn coatings in the art, the
present disclosure provides electroplating compositions, which when deposited on a steel
substrate in the manner described herein, provide coatings that show uniform, fine and compact
morphology. This morphology in turn provides excellent corrosion properties. The Zn coatings
provided by the compositions and methods of the present disclosure show better corrosion
resistance than the commercially used Zn-Ni coatings (FIGs. 5 and 6). As nickel is much more
costly, the Zn coatings of the present disclosure are cost-effective and at the same time provide
superior corrosion properties than the commercially used Zn-Ni coatings.
It is to be understood that the foregoing descriptive matter is illustrative of the disclosure and
not a limitation. While considerable emphasis has been placed herein on the particular features
of this disclosure, it will be appreciated that various modifications can be made, and that many
changes can be made in the preferred embodiments without departing from the principles of
the disclosure. Those skilled in the art will recognize that the embodiments herein can be
practiced with modification within the spirit and scope of the embodiments as described herein.
Similarly, additional embodiments and features of the present disclosure will be apparent to
one of ordinary skill in art based upon description provided herein.
Descriptions of well-known/conventional methods/steps and techniques are omitted so as to
not unnecessarily obscure the embodiments herein. Further, the disclosure herein provides for
examples illustrating the above-described embodiments, and in order to illustrate the
embodiments of the present disclosure certain aspects have been employed. The examples used
herein for such illustration are intended merely to facilitate an understanding of ways in which
the embodiments herein may be practiced and to further enable those of skill in the art to
practice the embodiments herein. Accordingly, the following examples should not be construed
as limiting the scope of the embodiments herein.

EXAMPLES
Example 1: Effects of varying concentrations of zinc sulphate
Electroplating compositions comprising zinc chloride (6 g/L), boric acid (30 g/L), and varying
amounts of zinc sulphate from 50 g/L to 500 g/L were prepared to test the effect of the zinc
sulphate concentration on the deposited coating. Lower concentrations caused burnt deposit at
the edges due to high current density whereas at higher concentrations, although higher
deposition kinetics (amount of coating deposited per minute) was achieved, the corrosion
resistance was better at relatively lower concentration of zinc sulphate. Zinc sulphate
concentrations in the range of about 200-300 g/L provided Zn coatings with uniform
morphology when deposited at a current density of about 170-190 mA/cm2, thereby providing
satisfactory corrosion properties.
Example 2: Effect of current density on the morphology of the Zn coating
An electroplating composition comprising 250 g/L zinc sulphate, 6 g/L zinc chloride, and 30
g/L boric acid was deposited on a steel substrate at varying current densities from 50 mA/cm2
to 250 mA/cm2 to test the effect of current density on the morphology of the Zn coating. FIG.
2 shows a comparison of the morphologies (grain structure) of the Zn coatings obtained at
current densities of 50, 150, and 250 mA/cm2.
Example 3: Effect of duty cycle and frequency of the pulsed current on the morphology
of the coating
An electroplating composition comprising 250 g/L zinc sulphate, 6 g/L zinc chloride, and 30
g/L boric acid was deposited on a steel substrate using a pulsed current having an average
current density of 180 mA/cm2, with variation in duty cycle of 25%, 50%, and 75% and
applying frequencies varying from 25 Hz, 75 Hz, and 200 Hz. FIG. 3 shows a comparison of
the morphologies/grain structure of the Zn coatings obtained with variations in duty cycle and
frequency of the pulsed current. Zn coatings obtained with moderate duty cycle (50%) with
high frequency (200 Hz) or high duty cycle (75%) with low frequency (25Hz) showed uniform
and fine grain structure.
Example 4: Effect of additives on the morphology of Zn coatings

An electroplating composition comprising 250 g/L zinc sulphate, 6 g/L zinc chloride, 30 g/L
boric acid, and CTAB or benzylidene acetone as an additive was deposited on a steel substrate
using a pulsed current having an average current density of 180 mA/cm2, with duty cycles
varying from 25%, 50%, or 75% and at a frequency of 25 Hz. Electroplating compositions
comprising CTAB at a concentration of 1 g/L or benzylidene acetone at a concentration of 0.07
g/L, when deposited at a duty cycle of 75% and frequency of 25 Hz, gave coatings with uniform
morphology, fine grain structure and very low corrosion current. See FIG. 4.
Example 5: Comparison with commercially available coating
The current commercially available products to provide corrosion resistance to steel substrates
are electrodeposited Zn-Ni alloy coatings. The Zn coatings of the present disclosure were
compared with the commercial Zn-Ni coating. For this, electroplating compositions were
prepared as shown in Table 4 below:

Table 4: Electroplating Compositions
Constituent Composition A
(g/L) Composition B
(g/L) Composition C
(g/L)
Zinc sulphate 250 250 250
Zinc chloride 6 6 6
Boric acid 30 30 30
CTAB - 1
Benzylidene acetone - 0.15 0.07
Composition A was deposited using both DC and pulsed current method. Composition B was
deposited using the DC method and Composition C was deposited using the pulsed method.
Deposition parameters employed in the DC and pulsed method are shown in Table 5.
Table 5: Parameters for DC and pulsed current deposition of Zn coatings
DC method Pulsed method
Current density: 180 mA/cm2 Current density: 180 mA/cm2 20
Stirring rate: 300 rpm Peak current density: 240 mA/cm2
Duty cycle: 75%
Frequency: 25 Hz
Stirring rate: 300 rpm

FIGs. 5 and 6 show the morphology and corrosion properties of the Zn coatings of the present
disclosure and those of the commercial coating (shown as “Benchmark”). The corrosion
potential of the Zn coatings of the present disclosure is more negative than that of commercially
available Zn-Ni coating, implying a higher sacrificial corrosion resistance. The corrosion
current is also lower than that of the commercially available coating. Also, the deposition rate
of the present coating is higher than that of the commercial coating. Thus, the developed Zn
coatings show a higher sacrificial protection to steel along with a much lower corrosion rate
than the commercially available coating and shows a higher deposition rate than the
commercial coating.

We Claim:
1. An electroplating composition comprising zinc sulphate, zinc chloride, and boric acid,
wherein the electroplating composition has a pH of about 3-4.5.
2. The electroplating composition as claimed in claim 1, wherein the zinc sulphate is present
in an amount of about 200-300 g/L, the zinc chloride is present in an amount of about 5-8
g/L, and the boric acid is present in an amount of about 22-35 g/L.
3. The electroplating composition as claimed in claim 3, wherein the zinc sulphate is present
in an amount of about 250 g/L, the zinc chloride is present in an amount of about 5-8 g/L,
and the boric acid is present in an amount of about 22-35 g/L.
4. The electroplating composition as claimed in claim 2 or 3, wherein the zinc sulphate is
present in an amount of about 250 g/L, the zinc chloride is present in an amount of about 6
g/L, and the boric acid is present in an amount of about 30 g/L.
5. The electroplating composition as claimed in any one of claims 1-4, comprising an additive
selected from cetyl trimethyl ammonium bromide (CTAB), benzylidene acetone, or a
combination thereof.
6. The electroplating composition as claimed in claim 5, wherein the CTAB is present in an
amount of about 0.5-2.5 g/L and/or benzylidene acetone is present in an amount of about
0.05-0.2 g/L.
7. The electroplating composition as claimed in claim 6, wherein the zinc sulphate is present
in an amount of about 250 g/L, the zinc chloride is present in an amount of about 5-8 g/L,
the boric acid is present in an amount of about 22-35 g/L, the CTAB is present in an amount
of about 2 g/L or benzylidene acetone is present in an amount of about 0.15 g/L.
8. The electroplating composition as claimed in claim 7, wherein the zinc chloride is present
in an amount of about 6 g/L and the boric acid is present in an amount of about 30 g/L.
9. The electroplating composition as claimed in claim 6, wherein the zinc sulphate is present
in an amount of about 250 g/L, the zinc chloride is present in an amount of about 5-8 g/L,
the boric acid is present in an amount of about 22-35 g/L, the CTAB is present in an amount
of about 1 g/L or benzylidene acetone is present in an amount of about 0.07 g/L.
10. The electroplating composition as claimed in claim 9, wherein the zinc chloride is present
in an amount of about 6 g/L and the boric acid is present in an amount of about 30 g/L.

11. A method for preparing the electroplating composition as claimed in any one of claims 1-
4, comprising:
a. heating water to about 50-60 ͦ Co obtain a heated water;
b. adding boric acid to the heated water to obtain a first solution;
c. adding zinc sulphate to the first solution to obtain a second solution;
d. adding zinc chloride to the second solution to obtain a third solution; and
e. adjusting pH of the third solution to provide the electroplating composition.
12. The method as claimed in claim 11, wherein an additive selected from CTAB, benzylidene
acetone, or a combination thereof is added to the first solution prior to adding zinc sulphate.
13. The method as claimed in claim 11 or 12, wherein each step is carried out under constant
stirring at a rate of about 250-350 rpm.
14. A method for depositing the electroplating composition as claimed in any one of claims 1-
8 on a steel substrate, comprising:
a. providing the steel substrate as a cathode;
b. depositing the electroplating composition on the steel substrate at a constant
current with a current density of about 170-190 mA/cm2 and at a stirring rate of
about 250-350 rpm to provide a steel substrate comprising a zinc (Zn) coating.
15. The method as claimed in claim 14, wherein the current density is about 180 mA/cm2.
16. The method as claimed in claim 14 or 15, wherein the Zn coating provided by the method
exhibits a corrosion current density of about 1.2-1.6 μA/cm2.
17. The method as claimed in any one of claims 14-16, wherein the Zn coating provided by the
method exhibits a corrosion potential of about -1.08 to -1.20 V.
18. The method as claimed in any one of claims 14-17, wherein the method provides a
deposition rate of about 1.5-4 µm/min.
19. A method for depositing the electroplating composition as claimed in any one of claims 1-
6 and 9-10 on a steel substrate, comprising:
a. providing the steel substrate as a cathode;
b. depositing the electroplating composition on the steel substrate by employing a
pulsed current with an average current density of about 170-190 mA/cm2, a peak
current density of about 240-720 mA/cm2, a duty cycle of about 25%-75%, and
a frequency of about 25-200 Hz; wherein the electroplating composition is

stirred at a rate of about 250-350 rpm during said depositing to provide a steel
substrate comprising a zinc (Zn) coating.
20. The method as claimed in claim 19, wherein the pulsed current has an average current
density of about 180 mA/cm2, a peak current density of about 240 mA/cm2, a duty cycle of
about 75%, a frequency of about 25 Hz, and wherein the electroplating composition is
stirred at a rate of about 300 rpm.
21. The method as claimed in claim 19, wherein the pulsed current has an average current
density of about 180 mA/cm2, a peak current density of about 240 mA/cm2, a duty cycle of
about 50%, a frequency of about 200 Hz, and wherein the electroplating composition is
stirred at a rate of about 300 rpm.
22. The method as claimed in any one of claim 19-21, wherein the pulsed current has ton of
about 30 ms and toff of about 10 ms.
23. The method as claimed in any one of claims 19-22, wherein the Zn coating provided by the
method exhibits a corrosion current density of about 1.0-1.7 µA/cm2.
24. The method as claimed in any one of claims 19-23, wherein the Zn coating provided by the
method exhibits a corrosion potential of about -1.08 to -1.15 V.
25. The method as claimed in any one of claims 19-24, wherein the method provides a
deposition rate of about 1.5-3 µm/min.