Acid Zinc

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A. Noack, SurFin 2009, Louisville, Kentucky

Acid Zinc Nickel

A new chapter in zinc nickel plating

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Development of corrosion protection

Advantages of zinc nickel coatings

Comparison alkaline vs acid zinc nickel

Application examples

Summary

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Summary

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4 A. Noack, SurFin 2009, Louisville, Kentucky


first use of Zn layers as corrosion protection

introduction of the dynamo mass production

introduction of cyanide alkaline processes

zinc nickel alloy predominantly alkaline based

mid 19th

century

1867

1920th

State of the art

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Summary

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Best corrosion protection

against red rust

Low contact corrosion in combination

with aluminum

Reduced white rust formation

High wear resistance

Very good temperature stability

Benefits


Best cathodic corrosion protection among

zinc and zinc alloy layers

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7/277 A. Noack, SurFin 2009, Louisville, Kentucky

Corrosion Performance

Time to Red Rust

panels without passivate

ISO 9227 NSS

750 h to Red Rust gamma phase zinc nickel

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Corrosion Performance

Protection relative to pure zinc (ISO 9227 NSS)

function of nickel concentration

Maximum gamma phase concentration with 12 16 % nickel

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Conclusion

Homogenous distribution of gamma phase deposition is crucial

Alkaline electrolytes ensure this

Alkaline zinc nickel robust well established but with limits

but

Alkaline zinc nickel electrolytes still state-of-the-art

limits for certain base materials hardened steel

cast iron

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Summary

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Introduction of a new generation ammonia-free acid zinc nickel

Does it come with the same properties as alkaline zinc nickel?

The new electrolyte extensive testing to prove perfomance

Series of investigation to prove

Surface Morphology

Crystallite Texture

Analysis for gamma phase

Influence of working parameters

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Surface Morphology

acidic electrolyte alkaline electrolyte

2.5A/dm

0.7

A/dm

All deposits share a globular morphology

SEM pictures - 10 kX magnification

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Morphology actual comparison

All samples clearly show the same columnar texture of field oriented

crystal growth

No significant difference is seen between both alkaline and the acidic

electrolyte

zinc nickel plated from alkaline electrolyte

Same columnar, field oriented texture with all deposits

zinc nickel plated from acid electrolyte

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XRD diagrams* actual comparison

XRD indicates -phase composition of all deposits*All XRDs recorded using Cu K x-ray.

alkaline zinc nickel with known -phase

2 A/dm; 8 m

acid zinc nickel

2 A/dm; 8 m

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New generation acid zinc nickelelectrolytes

Homogenous nickel incorporation is a must

Acid electrolytes are known to have worse metal distribution

compared with alkaline ones

First generation acid zinc nickel with weakness in

variation of Ni over current densities

variation of Ni with temperature

intensive testing to ensure operation window

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Influence of working parameters

constant -phase composition

Current density

XRD of acid zinc nickel deposits plated at different current densities from an ammonia free electrolyte

Lin(Counts)

0

1000

2000

3000

4000

5000

2-Theta - Scale

30 40 50 60 70 80 90 100 110 120 130 140

(330)

(600)

1.5 A/dm

(Cu K )

3.0 A/dm

0.5 A/dm

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Influence of working paramters

constant nickel distrubition over a wide working window

Current density

XRF analysis of nickel incorporation

Current density Nickel incorporation

3 A/dm 12. 8 %

1.5 A/dm 12.7 %

0.5 A/dm 13.7 %

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Influence of working paramters

no negative influence of temperature variation

Electrolyte Temperature

XRD scan of deposits plated at two different temperatures

Temperature Nickel

25 C 13.8 %

35 C 14.3 %

_ _ _

_ _ _

Log

(Counts)

1

10

100

1000

1e4

1e5

2e5

2-Theta - Scale

31 40 5 0 60

25 C

35 C

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Conclusion

new acid zinc nickel performs equal compared to alkaline electrolytes

in terms of

new acid zinc nickel more reliable than first generations

Surface Morphology

Texture

Gamma phase formation

new generation acid zinc nickel is less sensitive

to variation on current density

to variation in temperature

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Summary

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Common practice: use acid Zinc with trivalent passivate

Cast iron base material contains significant carbon concentration in the surface Fast initial plating is required for good coverage

Ammonia-free acid zinc nickel recognized for brake systems

Brake calipers

Adhesion

Delaminating

Increased quality demands ask for use of zinc nickel

up to now duplex systems were used: acid zinc strike alkaline zinc nickel

new acid zinc nickel allows direct plating on cast iron

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Brake calipers

Corrosion Resistance

Process sequence

no substrate corrosion after 1000 h

ammonia-free acid zinc nickel

trivalent chromium passivate

inorganic reactive sealer

assembly

subject to ISO 9227 NSS

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Application example

ABC

Fastener

Thickness distribution M10 x 60

comparable thickness distribution

Point alkaline zinc nickel electrolyte forbarrel plating

acid zinc nickelelectrolyte in barrel plating

A 10 m 10 m

B 7.2 m 6.1 m

C 6.1 m 5.4 m

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Fastener

Plating speed M10 x 60

19 % reduction of plating time achieved

alkaline zinc nickel electrolyte forbarrel plating

acid zinc nickelelectrolyte in barrel plating

Time to reach 10m in point A

0,85 A/dm 52 min 42 min

A

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Summary

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Summary

Increased demands on sacrificial coatings require more and more the use of

zinc alloys

zinc nickel provides best performance for commercially available zinc alloys

Formation of Ni2Zn11 gamma phase is crucial for the deposit performance

best corrosion protection with maximum concentration at 12 16 % Ni

Troubles with first ammonia-based acid zinc nickel electrolytes lead to broad

product acceptance of alkaline based electrolytes

New ammonia-free electrolyte shows same deposit properties than alkaline

based deposits

accepted already for the brake caliper industry

benefits for the fastener industry

a new chapter acid zinc nickel plating has started

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Documents

Acid Zinc