This work offers a synthesis of researches performed in laboratory and regards the nickel microalloying of hot galvanizing baths. Experiments followed the structural changes of both hot galvanizing bath and deposed layer with effect on layer properties.
Characterization of deposed layer and nickel microalloying of galvanizing bath performed by spectral chemical analysis, optical microscopy and X ray diffraction emphasized the structural constituents nature as well as changes shown up depending on nickel concentration of galvanizing bath. Correlation diagrams between deposed layer thickness and structural constituents were also made.
Experimental results emphasized a close interdependence between nickel concentration and microstructure. This allowed to settle the optimal nickel concentration required by galvanizing bath microalloying with maximum effect upon hot galvanizing coating properties

Adriana PREDA

Radu BOICIUC

Simona BOICIUC

The Annals of “Dunarea de Jos” University of Galati Fascicle IX Metallurgy and Materials Science

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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI 
FASCICLE IX METALLURGY AND MATERIALS SCIENCE, ISSN 1453 – 083X. NR 2 – 2005 
 
 
 
 
RESEARCHES REGARDING STRUCTURAL CHANGES DUE TO  
NICKEL MICROLALLOYING OF HOT GALVANIZING BATHS 
 
Radu BOICIUC1, Adriana PREDA1,  
Simona BOICIUC2
 
1 S.C. Uzinsider Engineering S.A. Galaţi, 
2“Dunărea de Jos” Galaţi University 
e-mail: boiciuc.simona@ugal.ro
 
ABSTRACT 
 
This work offers a synthesis of researches performed in laboratory and regards 
the nickel microalloying of hot galvanizing baths. Experiments followed the 
structural changes of both hot galvanizing bath and deposed layer with effect on 
layer properties. 
Characterization of deposed layer and nickel microalloying of galvanizing bath 
performed by spectral chemical analysis, optical microscopy and X ray diffraction 
emphasized the structural constituents nature as well as changes shown up 
depending on nickel concentration of galvanizing bath. Correlation diagrams 
between deposed layer thickness and structural constituents were also made. 
Experimental results emphasized a close interdependence between nickel 
concentration  and microstructure. This allowed to settle the optimal nickel 
concentration required by galvanizing bath microalloying with maximum effect 
upon hot galvanizing coating properties.  
 
1. Generals 
 
Experiments performed on a pilot plant used A5K steel 
strip (as per STAS 10.318) or A35 – 401 type (according to 
ZE French standard) and included coating by hot 
galvanizing of several samples (P1-P7 code) suitable for the 
following nickel concentrations in galvanizing bath: 0%; 
0,02%; 0,06%; 0,09%; 0,11%; 0,16% and 0,20%. 
Galvanizing technology used is the classical one. 
Samples were degreased, pickled, preheated for 30 
seconds, immersed in galvanizing bath for 60 
seconds and then freely cooled in air.  
 
2. Spectral chemical composition of 
deposed layer 
 
Spectral chemical analysis on coating layer 
performed by Baird DV 6 optical emission 
spectrometer got the results included in table  
no.1. 
 
Table no.1 – Spectral chemical composition (%) of samples 
 galvanized and microalloyed  by nickel 
 
Sample 
code Ni Fe Cu Pb Sn Cd 
P1 0 4.651 0.000 0.001 0.004 0 
P2 0.02 1.599 0.001 0.001 0.008 0.001 
P3 0.06 0.412 0.001 0.001 0.005 0.001 
P4 0.09 0.264 0.001 0.001 0.005 0.001 
P5 0.11 0.177 0.001 0.001 0.003 0.001 
P6 0.16 0.168 0.001 0.001 0.002 0.001 
P7 0.20 0.163 0.001 0.001 0.002 0.001 
 
 
 
 
 
 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI 
FASCICLE IX METALLURGY AND MATERIALS SCIENCE, ISSN 1453 – 083X. NR 2 – 2005 
 
 
 
It may be seen an important decrease of Fe content in 
the coating layer in the same time with increasing the 
degree of bath microalloying up to 11% nickel content. 
Over this value the Fe content will stay approximate 
constantly.  
 
3.  Structural methallographic determinations 
Methallographic analysis performed by 
Olympus microscope, endowed by data 
acquisition automatic system, on specimens 
sampled from galvanized steel sheets and 
galvanizing bath.  
Measurements results are given in table no.2. 
 
 
Table no. 2. Thickness of zinc layer and intermetallic  layers 
 
Zn layer thickness (eta)  [μm] Intermetalllic composes layer thickness [μm] Sample 
code     g1    g2    g3     g4     g5 Gm Zn     g6     g7     g8      g9     g10 gm Cmet
P1 31.64 32.52 30.77 29.10 29.84 30.77 48.35 49.77 48.52 50.25 50.11 49.40 
P2 46.61 42.19 48.41 48.34 46.59 43.43 37.55 34.89 37.07 35.16 36.93 36.32 
P3 58.89 57.16 56.87 58.02 58.89 57.96 15.85 15.82 15.81 15.26 15.82 15.71 
P4 61.73 60.68 60.65 60.65 61.54 61.05 14.85 15.59 15.49 15.94 15.77 15.53 
P5 71.19 71.24 71.22 71.19 70.95 71.16 15.70 15.33 15.78 15.43 15.20 15.48 
P6 69.25 69.34 70.11 70.08 69.53 69.66 15.82 15.27 15.84 15.83 15.83 15.72 
P7 70.34 70.86 70.64 71.48 71.20 70.84 20.21 19.13 20.23 20.21 20.19 19.99 
 
Note: gm – the average value of deposed layer 
 
Analyzing the results it may be remarked that changes 
of deposed layers thickness took place depending on Ni 
percentage added in the bath. 
Up to 11% Ni content inside bath the Zn layer thickness 
increase and intermetallic compounds layer thickness 
decrease are recorded. Over this value the 
deposed layers thickness is kept approximately 
steady and it is a relevant aspect on diagrams in 
figures no.1 and 2.  
0
20
40
60
80
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.2
[% Ni]
g 
Zn
 [m
m
]
 
Fig. no.1. Variation of Zn layer thickness  
depending on Ni content of metallic bath 
0
10
20
30
40
50
60
0 0.02 0.06 0.09 0.11 0.16 0.2
Ni [%]
G
ro
si
m
e 
st
ra
tu
ri 
in
te
rm
et
al
ic
e 
[m
m
]
 
Fig. no.2.  Variation of intermetallic 
compounds layer thickness depending on  
Ni content of metallic bath 
 
Gradually by increasing the nickel microalloying 
degree of galvanizing bath, metallographic analysis 
emphasized (figures no. 3÷6) important changes in deposed 
layer structure: 
- Finishing of Zn grains and apparition of Ni-Zn 
intermetallic compound disperse particles in eta layer; 
- Decreasing and finishing the layer in “palisade”; 
- Coalescence of Ni-Zn intermetallic 
compound particles precipitated in eta layer. 
 Metallic bath microalloying by nickel, 
even in very small concentrations, made 
essential changes of its microstructure (Fig. no. 
7÷12). 
 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI 
FASCICLE IX METALLURGY AND MATERIALS SCIENCE, ISSN 1453 – 083X. NR 2 – 2005 
 
 
 
 
Fig. no. 3 Microstructure of deposed layer,  
0 % Ni. (x 500). 1% nital attach. 
 
 
Fig. no. 4 Microstructure of deposed layer,  
0.06 % Ni. (x 500). 1% nital attach. 
 
Fig. no. 5 Microstructure of deposed layer,  
0.11 % Ni. (x 500). 1% nital attach. 
 
Fig. no. 6  Microstructure of deposed layer,  
0.20 % Ni. (x 500). 1% nital attach. 
 
   
Fig. no. 7 Microstructure of  the bath 0 % Ni. 
 (x 100). 1% nital attach. 
Zn large crystals with macles. 
Fig. no. 8 Microstructure of  the bath 0,02 % Ni.  
(x 100). 1% nital attach. 
Zn large crystals with tendency to form Zn-Ni eutectic.
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI 
FASCICLE IX METALLURGY AND MATERIALS SCIENCE, ISSN 1453 – 083X. NR 2 – 2005 
 
 
 
 
Fig. no. 9. Microstructure of  the bath  
0,06 % Ni (x 100). 1% nital attach. 
 Inhomogeneous eutectic structure in which very fine 
dispersed particles of Ni-Zn intermettalic  
compound show up. 
 
 
Fig. no. 10. Microstructure of  the bath  
0,09 % Ni. (x 100). 1% nital attach. 
Eutectic structure in which fine dispersed particles of 
Ni-Zn intermettalic compound show up. 
 
Fig. no. 11. Microstructure of  the bath  
0,11 % Ni. (x 100). 1% nital attach. 
Fine eutectic structure in which fine particle 
agglomeration of Ni-Zn intermettalic compound show 
up dispesed. 
 
Fig. no. 12. Microstructure of  the bath  
0,20 % Ni. (x 100). 1% nital attach. 
Fine eutectic structure in which globular particle 
agglomeration of Ni-Zn intermetallic compound show 
up. 
 
Large Zn crystals grained in the same time with Ni 
content increasing up to a very fine eutectic structure where 
the Ni-Zn intermetallic compound particles precipitated. 
Coalescence and crowding of these particles made in the 
same time with alloying percentage increasing.X ray 
diffractometric analysis confirmed the results got by both 
spectral chemical and metallographical analysis . 
Phases identified in metallic layer were  
- ( γ) gamma adherence layer : Fe5Zn21; 
- (δ) delta frail layer in ”palisade” : FeZn7; 
- (ξ) zeta intermediary layer - Fe3Zn10; 
      - (η) eta layer or pure Zn; 
      - NiZn3 intermetallic compound. 
Quantitative ratio of the first four phases 
varies depending on Ni content up to Fe3Zn10 
intermediary phase vanishing. 
NiZn3 intermetallic compound apparition was 
signaled in the same time with feeding the Ni in 
metallic bath, its quantitative ratio increasing 
direct proportional by this element content 
recording a level inside  0.11÷0.16% Ni range 
(fig. no. 13). 
 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI 
FASCICLE IX METALLURGY AND MATERIALS SCIENCE, ISSN 1453 – 083X. NR 2 – 2005 
 
 
 
0
2
4
6
8
10
12
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20
[% Ni]
N
iZ
n 3
 - 
ra
po
rt 
ca
nt
ita
tiv
 [%
]
 
Fig. no. 13. Variation of NiZn3 phase quantitative ratio 
 depending on Ni content of metalic bath 
 
Fine structure additionally hardened by NiZn3 
intermetallic compound, dispersed in pure zinc in 
quantitative ratio up to 10.8%, confers special resistance 
and corrosion properties. 
 
4. Conclusions 
 
Nickel microalloying of hot galvanizing bath 
determines essential changes of both bath and deposed 
layer microstructures. 
Fe content decreases by Ni content increasing up to 
0.11 % as a result of FexZny type layers decreasing and 
apparition of NiZn3  compound. 
Eta zinc layer thickness increases by 131% and that one 
of intermetallic layers decreases by 69% Ni in galvanizing 
bath. Over this value thickness stays steadily.  
Deposed layer structure records the following changes: 
- Decreasing and finishing the layer in “palisade”; 
- Finishing of Zn grains and apparition of disperse 
particles of Ni-Zn intermetallic compound in eta layer; 
- Coalescence of Ni-Zn intermetallic compound 
particles precipitated in eta layer. 
Large Zn crystals grained in the same time 
with Ni content increasing up to a very fine 
eutectic.  
NiZn3 intermetallic compound presence in 
deposed layer, in a quantitative ratio of up to 
7.5% suitable for 0.11% Ni content determines 
both structure finishing and additional hardening 
of coating with maximum effects on coating 
quality. 
 
References 
 
[1]. G. Reumont, P. Perrot, J. Foct - Thermodynamic 
study of the galvanizing process in a Zn – 0,1 % Ni bath, 
Journal of Materials Science 33, pg. 4759-4768, 1998. 
[2]. G. P. Lewis, J. Pederson - Optimizing the Ni-Zn 
process for hot dip galvanizing, Cominco LTD., 1998 
[3]. C. Alonso, J. Sanchez, J. Fullea, C. Andrade, P. 
Tierra, M. Bernal - The addition of nickel to improve the 
corrosion resistance of galvanized reinforcement, 1995 
[4]. D. Stroud - Galvanizing with Zn-Ni alloy, 
Proceedings first Asian-Pacific General Galvanizing 
Conference, Taiwan, 1992 
 
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Researches Regarding Structural Changes due to nickel Microlalloying of Hot Galvanizing Baths

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Researches Regarding Structural Changes due to nickel Microlalloying of Hot Galvanizing Baths

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