Product Introduction

Brightener series for zinc-nickel alloy plating
Stron Ni Zinc, High Ni Zinc, Acid Ni Zinc
Nippon Hyomen Kagaku Kabushiki Kaisha R & D center

Introductionsuspension parts, fuel system pipes, and other locations

Zinc and zinc alloy plating are widely used as anti-requiring high corrosion resistance.

corrosion plating for automotive parts. About 40 years ago,

Currently, the bath types of zinc-nickel alloy plating in thethe Canadian Code (1 year for exterior rust and 3 years formarket are classified as shown in Figure 1, and they are usedperforated rust, 1978) and the Nordic Code (3 years foraccording to the bath type and the nickel co-deposition rate

exterior rust and 6 years for perforated rust, 1983) werein the plating film. 2

issued with the goal of ensuring that the products could

Sulfate bathwithstand use under severe corrosive environments whereAcid bath

5 to 10% nickel ratio bath
Chloride bathsnow melting chemicals are applied in winter, such as North
America and Northern Europe. In the 1990s, the U.S.

Ammonium bath
13 to 18% nickel ratio bath

Potassium bath

13 to 18% nickel ratio bathautomotive industry established specific rust-preventive
5 to 10% nickel ratio bathcapabilities, including a voluntary 10-year rust-preventive

Alkaline bath

Zincate bath
13 to 18% nickel ratio bathstandard, etc. Around 1998, European manufacturers beganoffering a 12-year perforated rust warranty, and Japanese

Figure 1: Type of Zinc-nickel Alloy Plating

manufacturers followed suit. The anti-corrosion code wasthe catalyst for a major development in zinc alloy plating,

Product Summary

which offers more stable corrosion resistance than zinc

The JASCO brightener series for zinc-nickel alloy platingplating. 1

are available in both alkaline and acidic baths, and the lineup

Zinc alloy plating includes zinc-iron, zinc-cobalt, zinc-includes products with different nickel co-deposition rates tonickel, and tin-zinc. Among them, zinc-nickel alloy plating

meet a variety of quality requirements. (Table 1)

is widely used for parts around automobile engines,
Table 1: Brighteners for Zinc-nickel Alloy Plating
Product nameNi (%)

Stron Ni Zinc ZN-202

5 to 10Stron Ni Zinc ZN-208H

Stron Ni Zinc ZN-208J
Acid Ni Zinc AZN-6900
Acid Ni Zinc AZN-6900KPlating

plating bathmethod
Rack,
BarrelAlkaline

Stron Ni Zinc ZN-208K
High Ni Zinc ZN-204J

Type of13 to 18AcidNi (%): nickel co-deposition rate in plating film

Rack
BarrelFeatures
Ideal for plating with emphasis on bending
Available at high plating temperatures

Rack,

Iron plate can be used as anode,Barrelimproved current efficiency reduction

Rack,High current efficiency

BarrelBoron and ammonia free
202010301 JASCO Nippon Hyomen Kagaku Kabushiki Kaisha 1

[Product Introduction] Brightener series for zinc-nickel alloy platingDegreasing

Electrolyticcleaning

PicklingPlating

Chemicalpassivation

Activation

DryingFigure 2: Zinc-nickel Alloy Plating Process (general processing process)Features of brighteners for zinc-nickel alloy plating

zinc plating while having sacrificial corrosion protection. 2・ZN-202: ideal for pipe parts that are bent after plating

It also has high heat resistance and little degradation of・ZN-208H, ZN-208K: operation at a plating temperature ofcorrosion resistance in high temperature environments

30°C reduces cooling costs.

(Figure 3). For this reason, it is often applied to areas where・ZN-204J, ZN-208J: the use of iron plate anodes reduceshigher corrosion resistance is required, or to areas used in

the amount of brightener replenishment and the loss ofhigh-temperature environments, such as around engines.

current efficiency.

The reasons for this are explained in terms of corrosion

・AZN-6900: high current efficiency, ideal for iron castings,

potential and spreading of corrosion currents.

small screws, etc.

1. Corrosion potential

・ AZN-6900K: excellent wastewater treatability due toTable 2: Natural Potential of Metals in Seawater (vs. SCE)

boron and ammonia freeMetal
NickelIronZinc

All products can be analyzed for bath composition andnickel stabilizers, thereby maintaining stable plating quality.

Natural potential (Ｖ)
-0.24
-0.65
-1.07

When two metals are brought into contact in a corrosive

Treatment processenvironment, a battery is formed due to the potential

The treatment process for zinc-nickel alloy plating isdifference between the metals. The base metal (metal on thesimilar to that for zinc plating, but organic acids are

low potential side) becomes the anode and dissolves, while

generally used for activation after plating. (Figure 2)

the noble metal (metal on the high potential side) becomesthe cathode and inhibits corrosion (sacrificial corrosion
prevention function).

Mechanisms
The most significant feature of zinc-nickel alloy plating isthat it has three to five times higher corrosion resistance thanElapsed time (h)Dryingcondition

06

2448

72

96

120

168

240

360

480

600

720

840

1008

1200

1440

1680

1920

2160

2400

80°C
Zn plating+

20 minTrivalent
chromiumpassivation

Zn-Ni

150°C
24 h80°Calloy
plating

20 min+Trivalent
chromiumpassivation

150°C
24 h

Figure 3: Comparison of Zinc plating and Zinc-nickel Alloy Plating by Salt Spray Test
202010301 JASCO Nippon Hyomen Kagaku Kabushiki Kaisha 2

[Product Introduction] Brightener series for zinc-nickel alloy plating

When galvanized iron is present in seawater, the naturalpotential of zinc is -1.07 V (vs. SCE), while iron is -0.65 V(vs. SCE), so zinc becomes the anode and dissolves, whileiron becomes the cathode and inhibits corrosion. On theother hand, in nickel plating, the sacrificial corrosion
protection function does not work because the naturalpotential of nickel is -0.24 V (vs. SCE) while that of iron is-0.65 V (vs. SCE). (Table 2)

Before salt spray

After salt spray

Figure 4: Zinc-nickel Alloy Plated Surface Before and After
Salt Spray
Plating type: alkaline zincate bath (Ni: 13 w%)

The large potential difference between zinc and iron (0.42

Test condition: salt spray JIS Z2371, 48 hV) has a high sacrificial corrosion protection effect on iron.
However, due to the high dissolution rate of zinc, the zincdisappears early, and the sacrificial corrosion protection

In closingeffect also decreases. If the potential difference can beZinc-nickel alloy plating is an indispensable technology

reduced by making the potential of the plating film closer tofor automotive parts and other steel industry products and isthat of the steel material, the dissolution rate of the plating

particularly suitable for areas subjected to heat or requiring

film itself will be reduced and the duration of the sacrificial

high corrosion protection. JASCO's zinc-nickel alloy plating

corrosion protection effect can be extended. 3brightener series can be used for a wide range of applicationsIn the case of zinc-nickel alloy plating, the naturalpotential of the plating film itself approaches iron due to thethanks to its long track record in the field and extensive
lineup.

co-deposition of nickel in the plating film, and the differencein electrode potential between the plating film and theReferencesmaterial metal becomes small. In this case, by controlling

1: Thethe electrode potential so that it does not become more noble

Statueand Challenges of Automobile Corrosion andthan iron, a long-term sacrificial corrosion protection effectCorrosion Protection -The 1st Report of Automobile

can be obtained.

Corrosion Sub-committee Activity-, pp. 4-64 (2017)

2. Spreading of corrosion currents

2: Nippon Hyomen Kagaku Kabushiki Kaisha, Technical

Under the corrosive environment of salt spray test, zinc

186th

husyokubousyokusinpoziumu,Current

News, Nos. 181, 186, 204, 235

electrochemically dissolves preferentially compared to

3: Minoru Hiramatsu, Makoto Hino, Takashi Omi, Current

nickel. This causes stress in the plating film, resulting in theTrend in Development of Corrosion Protective Plating,formation of micro cracks on the plated surface (Figure 4).

Zairyo-to-Kankyo, 45 pp. 33-41 (1996)

The micro cracks become finer as the corrosion progresses,

4: Hideki Hagi, Hiroyuki Yotsugi, Corrosion Process ofresulting in spreading of the corrosion current and a

Zinc-Nickel Alloy Electroplated Steel. Journal of thereduction in the corrosion rate. At this time, a non-Surface Finishing Society of Japan 48, pp. 206-212 (1997)

conductive ZnCl2/4Zn(OH)2 layer is formed, which acts asa protective film and suppresses the progress of corrosion.4202010301 JASCO Nippon Hyomen Kagaku Kabushiki Kaisha 3