Surface Coating Alloys

7/31/2019 Surface Coating Alloys

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Surface Coating Alloys


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Why surface coating?

Annual loss due to corrosion isestimated to be 3-5 % of GNP, about80,000 Cr `/ year

Direct Loss: material cost, over design,use of costly material

Indirect losses: loss of production,contamination of product, liability inaccidents


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Corrosion inIndia


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Coated Steels

Most common metallic coating forcorrosion protection of steel is a zinc(sacrificial coating)

Offers Barrier and Galvanic protection

Scrat

ch ElectrolyteZincCoatingSteel

Substrate

Zinc

and

Steel

forms of alloy

used Zinc, PureAl,

Al-Zn and

Zn-Al-Si alloy


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Surface Coating Alloy composition usedworldwide

Chemical Composition(%)

Zn Si Fe Al

43 ---- -- 55

12-24 Up to 4 0.25 Balance

12-24 0.3-4 0.3-3.5 Balance


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AlZnSi Alloy (Galvalume)

Minex manufactures Pre-mixed

AlZnSi alloy and

Aluminum Silicon master alloys

AlZnSi Alloy

- assures consistent alloy chemistry

- ease of addition and control

- close control on coating bath


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Minex Manufacturing Facilities

Coating alloysmanufactured at Nimji

2 set of 1MT InductionFurnace

1MT Uni DirectionalStirring Furnace


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ISO 9001:2008 andNABL accredited labfacilities

Adherence to strictquality control during

production andprocess


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Alloys manufacturedwith ASTM standardsand specifications

500 Kgs to 1MT castsize or Custom sows

for large capacity

Use of AlSi 50% alloy

for close control of

d i


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Raw MaterialAluminum Melt +

AlSi50 & Zinc Metal

Weighing as perrequirement

RM Inspection by Lab

Transfer Aluminum Meltfrom Skelner Furnace to

UDS

(temp. 70015C)

Dissolve AlSi50 alloy inAluminum Melt

After dissolution clean dross(temp. 76015C)

Zn Metal added in AlSi meltTill homogenization

Cleaning of C.I.mould, maintain

mould temp in range150C max, with

mould wash coating

Sample token is withdrawnfor Chemical Analysis

Dilution or addition ofmaterial depends upon

sample analysis

Alloy Casting in C I mould(temp. 68515C)

Results Analyzedwith ED-XRF

Ingot Surface FinishAnalyzed for packing &

dispatch

Mould:Mass ratio >1.5is for better heat

dissipation

ProductionProcessRM used

EC grade Al

AlSi 50

Zn metal???

Element Al Si Fe Others

% 99.70 0.10Max

0.20Max

traces

Element Al Si Fe Ca

% 50.0 50.0

Max

0.20

Max

0.10

Max

Element Zn Si Fe others

% 99.0 0.20

Max

0.20

Max

0.10

Max


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Minex Alloyfor Surface Coating

AlloyGrade

Chemical Composition (%)Al Zn Si Fe

(max)Cu(max)

Cd(max)

Pub(max)

Sn(max)

Ni(max)

Ti+Ba+Cr(max)

Al-Zn-Si

Alloy

55 -

58

41-

43

1.5-2 0.25 0.03 0.05 0.01 0.05 0.05 0.05

Alloy

Composition

Ingot Forms

AlSi 3% Finished AlloyElement Si Fe Others Al% 2.8-3.2 0.20 max Trace Balance


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Advantage

AlZnSi coating alloy v/s AlSi master alloy

Coating alloy directly melted in coating

tank Consistent alloy chemistry restricts

charge balance for each alloy addition

Alloy chemistry designed with closetolerance over tramp and impurities

High degree of homogeneity with UDSfurnace


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Advantage and Effects

Corrosion performance is mostly relatedto Al Zn alloy,

Silicon addition minimize the growth of

brittle intermetallic layer of steel andzinc

during Hot Dip Process.


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Al-Zn-Si alloy microstructure2 layers i.e.an Al Zn overlay coating and Fe

containing intermetallic/alloy layer.

Alloy layer forms at the interface between thecoating and steel substrate.

Due to this, Al Zn Si Alloy combines the Galvanic corrosion protection of Zn with the barrier protectionof Aluminum


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thank

you!

Surface Coating Alloys

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