FIELD OF INVENTION
The present Invention relates to an improved coating material of steel. More
particularly the present invention relates to an Improved Zn-A! alloy coating
adaptable to steel materia! to increase corrosion property and the process of
BACKGROUND OF THE INVENTION WITH PRIOR ART DIFFEICULTIES
Building materials, structures, white goods and automobiles made of iron and
steel and steel are coated with molten zinc for protection against corrosion.
Cathodic protection (CP) reduces corrosion by changing the thermodynamics of
the steel, i.e, the chemical potential of steel is changed to make it more inert.
More electropositive material like Zn. fig and A! have a tendency to give
sacrificial protection to base steel where the coating material is likely to be
damaged and the base metal remain free from corrosion.
A series of long term exposure test reported that galvanized coating delay the
onset of corrosion in marine environment, but do not prevent it completely. An
eleven-year exposure programme In marine environment revealed that the Zinc
coating suffered 2 to 3 mil loss )n thickness of the original zinc layer due to
corrosion,
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Zine is an amphoteric metal, it is stable in a specific range of pH 6-12 only and
corrosion behavior of galvanized steel In the presence of chlorides is controlled
by the medium pH. Ductility of the coating of pure Zinc coated materia! is very
poor due to presence of thick brittle phase zeta phase. Alloying element like
copper and cadmium is harmful for ductility of the coating. Addition of nickel in
Zinc coating reduces the hydrogen evolution reaction as well increase the
corrosion resistance property against chloride. The minimum requirement of
nickel in a Zinc-nickel alloy is 12 wt % for drastic improvement in corrosion
resistance against chloride ions, Alloy making with such composition is cost
prohibitive and difficult due to wide difference of their melting temperature.
The addition of 0.18-0.02% Al to the bath leads to the rapid formation of an Al-
Fe phase (Fe^Ah or Fe-Al-Zn) which inhibits the growth of Fe-Zn intermetallic
compounds snd therefore improves the mechamlca! properties of galvanized
steel.
Zn- A! alloy have a better corrosion resistance property than pure Zinc in
aggressive chloride environment. 5% A!-Zn alloy is nobler than Zinc. The passive
current densisties of Zn-5AI alloy bath is advantageous to improve bath fluidity.
Considerable efforts have teen made In recent years to Improve the
characteristic of galvanized coatings, particularly corrosion resistance, the
addition of various alloy to the bath were proposed of which Ai, and Mg seemed
particularly particularly Interesting.
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To solve the disadvantages of the prior state of art m the present invention an
alloy coating process of Zn has been development on different grades of steel
substrate in various forms. The new alloy coating have significant improvement
of coating properties regarding its enhanced corrosion resistance in industrial
environment and adverse saline environment description
OBJECTS OF THE INVENTION
It is thereof, an object of the present invention to propose an improved Zn-A!
alloy coating adaptable to steel substrate to Increase the corrosion property
which eliminates the disadvantage of prior Art.
Another object of the present invention is to propose an Improved Zn-A.l alloy
coating adaptable to steel subtract which develops significant improvement in
coating properties,
A still another object of the present invention, is to propose an Improved Zn-AI
alloy coating adaptable to steel subtract which Is feasible for both as well as
continuous galvaning route.
A. ftirther object of the present invention. Is to propose an improved Zn=A! alloy
coating adaptable to steel subtract which is feasible for annealing as well as
flexing route,
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A still further object of the present invention is to propose an improved Zn-Al
alloy coating adaptable to steel subtract which increases the corrosion resistance
against aggressive saline environment increased up to 10 times for same coating
thickness.
An yet further object of the present invention is to propose an improved Zn-A!
alloy coating adaptable to steel subtract which Increases resistance against white
rust form action upto 10 times for the same coating thickness.
A still further object of the present Invention Is to propose an improved Zn-Al
alloy coating adaptable to steel subtract which improves signification in ductility
property of the coating.
DETAILS DESCRIPTION OF THE INVENTION
From the present invention various grades of steel in various forms can be
coated by different Zn alloys through hot dip route. Process route can be
annealing or fluxing before dip In galvanizing bath, Coating property very much
depends on stee! as well as Zn bath composition, dipping time, temperature and
cooling media, The new alloy coated steel surface shows significant
Improvement of corrosion resistance against aggressive saline, Industrial and
rural environments and powdering index (see Table IV). Powering index is
defined as comparative weight loss of the coated steel after deformation respect
to standards. It Is defined ~m a scale of ranges 1 to 10 Higher Powdering Index
indicates higher weight loss.
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WE CLAIM
1, An improved Zn-A! alloy coating adaptable to steel substrate for
increasing corrosion resistance property in different corrosion
environments comprising:-
a Zn-AI alloy containing 0.25 wt% A! and rest Zn
2= The Zn-A! Coating as claimed in claim 1 wherein the said coating is
applicable In all steel substrate like wire, pipe, rebar and sheet metal,
3. The Zn, Al Coating As claimed in Claim iwherein the said coating is
applicable to high media low carbon grinded structural steel,
4. The coating as claimed 1 wherein corrosion resistance against
aggressive saline environment increased up to 8 times for same coating
thickness,
5. The coating as claimed m claim 1 wherein corrosion resistance against
industrial environment increased up to IStimes for same coating
thickness.
6. The coating as claimed in claim 1 wherein resistance to rust formation
increased upto 9 times for same coating thickness,
7. The coating as claimed in claim i wherein powdering index drop down
to 3.

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An improved Zn-Al alloy coating adaptable to steel substrate for
increasing corrosion resistance property in different corrosion
environments comprising:-
a Zn-Al alloy containing 0.25 wt% Al and rest Zn