Available online at www.sciencedirect.com
ScienceDirect
Procedia Materials Science 9 (2015) 377 – 386
International Congress of Science and Technology of Metallurgy and Materials, SAM – CONAMET 2014
Zinc + nickel + microparticles coatings: production process and structural characterization
Zulema A. Mahmuda,*, Franco Amelottia, Carlos Serpia, Jorge Maskaricb, Martín Mirabalb, Norma Mingoloc, Liliana Gassad, Paulo Tulioe, Gabriel Gordillof
aINTI, Av. Gral Paz 5445 Procesos Superficiales Ed 46. CC 157-1650 San Martín. Argentina bDropur S.A. L N Alem 3560, Munro, Buenos Aires, Argentina
CCNEA. Comisión Nacional de Energía Atómica, Buenos Aires, Argentina dInstituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, INIFTA, UNLP, Argentina
eUniv. Tecnológica Federal do Paraná UTFPR/PR, Brazil fFacultad de Ciencias Exactas y Naturales, UBA, Argentina
Abstract
The properties of coatings obtained from Ni-Zn electrodeposition baths containing microparticles is analyzed. The incorporation of alumina or silicon carbide microparticles improves properties of hardness and protection of the coating. The Ni content in the alloy, which normally varies between 10 and 15 %, was measured by X-ray fluorescence. ZnNi-particles coatings show a high nickel content and high corrosion resistance. The incorporation of uniformly distributed particles in the coatings is achieved under controlled conditions of current density and mechanical stirring. It was found that in the present case, 8 A/dm2 is the optimal electrodeposition current density. Frontal coatings samples were studied by scanning electron microscope while cross sectional area by optical microscope. The surface analysis was performed by energy dispersive X-rays spectroscopy microprobe and the structural characterization by X-ray diffraction. The last technique showed that the phase (3,3,0) is reinforced after 10 minutes of electrodeposition in the presence of CSi, while there is a change from ZnNi (3,3,0) to ZnNi (1,1,0) in the presence of Al2O3. This led to an increment of the compressive forces in the material. The charge transfer resistance (RTC) of the coating depended on its own thickness. High values of RTC corresponded to lower values of corrosion current J0. Experimental results showed that RTC10 microns> RTC 20 microns > RTC5 microns, indicating that the best properties of the material were obtained at 10 microns. In industrial scale process and in the laboratory, it was found that electrolyzing during 10 minutes with different J is: RTC(8 A dm-2) > RTC(10 A dm-2) > RTC(6 A dm-2). Zn-Ni-CSi coatings showed a decrease in the crystal size when saccharin is added to the electrodeposition solution. ©©22001155TThheeAAutuhtohros.rPs.uPbluisbhleisdhbeydEblyseEvilesrevLitedr. TLhtdis. is an open access article under the CC BY-NC-ND license (Phettepr:-/r/cerveiaetwiveucnomdemr ornes.poorgn/slicbeinlisteys/obfyt-hnec-Sndc/i4e.n0t/i)f.ic Committee of SAM– CONAMET 2014. Peer-review under responsibility of the Scientific Committee of SAM–CONAMET 2014 Keywords: Surface treatments; Zn alloys; electrocomposite; coatings; corrosion proteccion; texture; saccharine; additives
* Corresponding author. Tel.: +54-11-4-724-6333; fax: +54-11-4-724-6313. E-mail address: zulema@inti.gob.ar
2211-8128 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Scientific Committee of SAM–CONAMET 2014 doi:10.1016/j.mspro.2015.05.007
378
Zulema A. Mahmud et al. / Procedia Materials Science 9 (2015) 377 – 386
1. Introduction
The corrosion resistance of zinc (Zn) can be improved by alloying Zn with nickel (Ni), iron or cobalt. ZnNi coatings have high hardness and best decorative Zn properties [Mosavat et al. (2011), Mahmud (2010 tesis)].
The steel sheets coated with ZnNi, particularly those whose composition is about 11-14 % Ni, are widely used in panels of the automobile industry due to its superior corrosion resistance, malleability, weldability, are much better than those of Zn [Espenhahn et al. (1992), Soepenberg et al. (1992), Ichida (1995), Fratesi et al. (1996)].
Rajagopalan (1970) and Winand (1994) have reported that alloys containing 20 to 25 % nickel are six times harder than zinc. The codeposition of Ni and Zn was first studied by Schoch and Hirsch (1907) using sulfate solutions with the addition of ammonium sulfate and aluminum sulfate. They remarked the importance to note that the greater the Ni content in the alloy the material resistance against corrosion is higher [Mahmud (2010)].
Beltowska and Lehman (2002) showed that ZnNi electrolyte is stabilized with an additive containing acetate at pH values between 2 and 5.2. An increase of pH leads to a decrease in the nickel content in the coatings for the complexation of acetates, in this case all depends on surface pH and the reaction during the electrolysis.
Byk et al. (2008) have studied the behavior of alloys produced from bath compositions over a wide range. It has been shown that changing the bath composition and the deposition conditions may appear normal or anomalous codeposition of Zn and Ni.
I. Brooks (1998) found that ZnNi alloys hardness could be related to an increase of Ni content in the alloy and it is independent of grain size and texture. Furthermore, the mechanical properties of the material depend stoichiometrically (ZnxNiy) on its composition. It is known that usually an increase in the thickness involves an increase in resistance to corrosion, was reported by D. Thomas (1984). In this work we have studied the correlation between thickness, texture [Mahmud et al. (2010)] and corrosion resistance [Mahmud et al. (2012)]. Applying independent techniques it was found that the texture changes are related to the thickness of the coating and also to the corrosion resistance in both Zn and in Zn and Ni alloys [Mahmud (2013)]. The study of the microstructure has shown brighter coatings when saccharin is added to the Ni-Zn electrodeposition bath [Park and Szpunar (2000), Oniciu and Muresan (1991), Mahmud et al. (2009)].
2. Experimental procedures
The experiments were carried out in a conventional electrolysis cell. The solution was Zn sulphate 1 M and Ni sulphate 1 M in acid media with pH = 3, with alumina or silicon carbide micro particles (2-6 μm diameter). Electrodeposition was performed under mechanical agitation to attain higher mass transfer to the cathode. The electrolysis was made by applying a current density of 8 A/dm2 for different electrolysis times (5-30 min). Finally, we removed the particles attached to the surface by using ultrasound. We have used SEM: scanning electron microscope, EDX: energy dispersive X-ray analysis and optical microscope to observe the cross-sectional area samples of Zn-Ni plus particles on steel included in epoxy resin cured and polished with 600 emery paper. The nickel content and the coating thickness were measured with an X-ray fluorescence (XRF) equipment. Microhardness was quantified with a Leitz Miniload 2. For determining the Zn-Ni hardness, an appropriate load of 25 g was used, which was obtained according to the coatings (from tables). In the texture measurements, the samples were prepared at 8 A/dm2 with deposition times of 5, 10, 20 and 30 minutes. The measurements were performed with a potentiostat-galvanostat EGG Princeton Applied Research Par 273 and 273 A. Electrochemical Impedance measurements (EIS) were carried out at open circuit potentials in the frequency range from 0.005Hz to 105 Hz. The studies of the effect of saccharin as an additive were made by XRD and XRF. For these purposes, the samples were prepared by galvanostatic electrolysis at current density 8 A/dm 2 for 10 min at different saccharine concentrations. The solution of Zn and Ni salts with the addition of micro particles of CSi or micro particles of Al2O3 plus saccharin additive at concentrations 1.2 × 10-4 M to 5.0 × 10-4 M and then the electrolysis with con8 Atrolled stirring bath along the cathode at room temperature.
Zulema A. Mahmud et al. / Procedia Materials Science 9 (2015) 377 – 386
379
3. Results and discussions
3.1 Incorporation of particles
The incorporation of a particle into the coating is shown in the area indicated in Fig. 1(a) and its EDX spectrum analysis is shown in Fig. 1(b).
Analysis of Ni % vs J (current density) at different particles concentration, was measured by X-ray fluorescence and the microhardness was measured in a microdurometer (charge: 25 g) and are shown in Fig. 2.
3.2 Nickel content vs J and Al2O3 concentration. Microhardness vs J and CSi concentration
Fig. 2(a) shows that an increment of the amount of particles into the electrolytic solution produces an increment in the content of Ni in the surface alloy. Likewise, the values of hardness Hv (Vickers) also increase with the increment of the particles concentration in the electrolytic solution, see Fig. 2(b).
(a)
(b)
Al
Zn
Zn
Ni
Fig. 1. Photomicrograph by SEM and EDX of ZnNi alloy coatings with (a) alumina particle incorporated; (b) spectrum analysis in a zone of 20 μm × 20 μm: the elements are Zn, Ni and Al (from alumina) were found in the particle.
380
Zulema A. Mahmud et al. / Procedia Materials Science 9 (2015) 377 – 386
Ni (%)
15,0 14,5 14,0 13,5 13,0 12,5 12,0 11,5 11,0
5
ZnNi in bath
(a)
+ Al O g/l 23
0
20
60
10
15
20
25
30
j (A/dm2)
Hardness (Hv: Vickers)
400 350 300 250 200 150
16
(b)
ZnNi in bath + CSi in g/l
0 20 60
18
20
22
24
26
j / (Adm-2)
Fig. 2. ZnNi with microparticles: (a) Ni content in ZnNi alloy coating vs j at different Al2O3 concentration in the solution and (b) Microhardness vs j at different CSi concentrations in the solution.
Zulema A. Mahmud et al. / Procedia Materials Science 9 (2015) 377 – 386
381
3.3 Coating phases and Thickness
We have studied samples with different thicknesses in attention to the importance of choosing a material that resists more drastic conditions in service. We have prepared the specimens at J = 8 A/dm2 because at this current density, the thickness deposited is compatible with industry requirement.
The textures were measured by XRD, and the present phases were determined. The predominant phases in ZnNi coatings are J (3,3,0) and Zn (0,0,2) or phase K (1,1,0) for alumina, see Fig. 3. The presence of SiC J (3,3,0) is reinforced for thicknesses greater than 10 microns (10 minute electrolysis), see Fig. 3(b). In the presence of Al2O3 a maximum of intensity shows that the alloy crystallizes in phase K (1,1,0), Fig. 3(c). According to XRD analysis the material presents compressive forces, which is an important property in the case where cracks are present in the alloy. In Fig. 3(b) there is a reinforced intensity vs thickness, at 10 μm, with CSi. In addition, in Fig. 3(c) there is a maximum of intensities in arbitrary unities indicating that a change to phase K(1,1,0) occurs, generating compressive forces. In this case a best material is obtained. From Fig. 3, we have found an optimum thickness 10 μm, in the presence of microparticles.
(a)
(b)
(c)
Thickness in μm
Thickness in μm
Thickness in μm
Fig. 3. XRD - FDP “pole figures extracted data from XRD studies”. Intensities vs thickness for ZnNi obtained at 8 A/dm2 for thickness: 5 μm, 10 μm, 20 μm. ZnNi (a) without partícles; (b) with CSi 20 g/l; (c) with Al2O3 20 g/l. In the horizontal axis the time in minutes is proportional to the
thickness.
382
Zulema A. Mahmud et al. / Procedia Materials Science 9 (2015) 377 – 386
3.4 Characterization of ZnNi coatings by EIS and polarization curves
Values of charge transference resistance (RTC) and J0 were obtained applying EIS and polarization curves. Results for different thickness of coating obtained at 8 A/dm2 are shown in Table 1.
ZnNi e / μm
5 10 20
Table 1. Characterization of material a j= 8 A/dm2 with several thicknesses 5 μm, 10 μm, and 20 μm.
EIS- RTC ( cm2)
Polarization Curve Corrosion Current J0 (ȝA/cm2)
Sin part.
CSi
Al2O3
Sin part.
CSi
4000
10000
7000
1,2
20
Al2O3 18
2000
13000
20000
1.9
1.5
1.0
5200
6300
7500
4.0
4.0
1.0
The RTC values are large for 10 μm, with particles. J0 corrosion currents are low. In these conditions the material performance is better at the optimum thickness of 10 μm.
3.5 The influence of saccharine on the corrosion current J0
Polarization curves in Fig. 4, show that J0 (corrosion current) increases when the saccharin concentration is increased in the ZnNi+CSi electrodeposition bath. On the other hand there is a shift on the corrosion potential towards negative values.
1E-5 1E-6
8Adm-2 10 min Tafel in NaOH 0.1N ZnNi + CSi 20g/l +saccharine
0 1.2 X10-4 M 5.0 X10-4 M
J (A/cm2)
1E-7
1E-8
1E-9 -0,9 -0,8 -0,7 -0,6 -0,5 -0,4 -0,3 -0,2 -0,1 0,0
E/V
Fig. 4. Polarization curves ZnNi + CSi (a) without saccharine, (b) with 1 × 10-4 M saccharine, (c) with 5 × 10-4 M saccharine in Na OH 0.1 N with buffer boric borate, pH 9.2. Scan rate v = 1 mV/s.
Z" (:
Zulema A. Mahmud et al. / Procedia Materials Science 9 (2015) 377 – 386
383
25000 20000 15000
(a)
8Adm-2 10 min
Nyquist in NaSO 0.1N 4
ZnNi + CSi 20g/l +saccharine
0
1.2 x 10-4 M
5.0 x 10-4 M
10000
5000
0 0
5000 10000 15000 20000 25000
Z´(:
30000
(b)
25000
20000
ZnNi bath + CSi +saccharine
0 1.2 x10-4 M 5.0 x10-4 M
IZI / :
15000
10000
5000
0
0,1
1
10
100 1000 10000
frequency / Hz
Fig. 5. EIS curves obtained in Na2SO4 0.1 M, pH 6.0. Scan from 100 KHz to 5 mHz. ZnNi +CSi (20 g/l) + saccharine: 0 (squares), 1.2 × 10-4 M saccharine (circles), 5.0 × 10-4 M saccharine (triangles). (a) Nyquist Diagram Z'' (imaginary component) vs Z' (real component);
(b) Bode Diagram |Z| vs. frequency.
Coatings obtained using solutions without saccharine show the same RTC value of those produced from solutions with a concentration 10-4 M of this additive, but in the last case with a better microstructure and reduced crystal size.
384
(a)
Zulema A. Mahmud et al. / Procedia Materials Science 9 (2015) 377 – 386
(b)
(c)
(d)
Fig. 6. Photomicrograph obtained by SEM in ZnNi coatings obtained at 8 A/dm2 10 min (a) without particles, (b) with CSi, (c) with CSi + 1.2 × 10-4 M and (d) with CSi + 5.0 × 10-4 M.
Fig. 7. shows that the Ni content decreased as the saccharin concentration increased to 5.0 × 10-4 M.
3.6 X-ray diffraction XRD studies, presented in Fig. 8, show the intensities of the phases obtained in the deposition conditions at variable J values for a deposition time of 10 min. It is known that in the ZnNi the J (3,3,0) phase is always present with varying intensity and depends on the coating.
16
14
12
Ni (%)
10
8
6 2
5x10-5M sac 20g/l CSi 20 g/l CSi + 1.2X10-4M sac 20 g/l CSi + 5.0X10-4M sac
4
6
8
10
J (A/dm2)
Fig. 7. Ni (%) vs J for different ZnNi compositions in the bath. black 5 × 10-5 M saccharine, blue CSi 20 g/l, pink CSi 20 g/l + 1.2 × 10-4 M, red CSi 20g/l + 5.0 × 10-4M.
Intensity / (c / s)
Zulema A. Mahmud et al. / Procedia Materials Science 9 (2015) 377 – 386
385
Phase J3,3,0)
1400
ZnNi 10 min, electrolysis
(a)
1200
with additions 5x10-5M sac
CSi 20g/l
1000
CSi +1,2x10-4M sac CSi +5,0x10-4M sac
800
600
400
200 2345678
j (A / dm2)
Intensity / c / s
Fase Zn 0,0,2)
450 (b)
400
350
300
250
200 150 100 50
ZnNi 10 min, de elect. with adittions
5x10-5M sac CSi 20g/l CSi +1,2x10-4M sac CSi +5,0x10-4M sac
2345678 j (A / dm2)
Fig. 8. Intensities of present phases in the ZnNi coatings with CSi microparticles and saccharine I vs j (A/dm2). (a) phase (3,3,0); (b) phase Zn (0,0,2).
The ZnNi phase Zn (0,0,2) seen in Fig. 8(b) shows that ZnNi in the presence of SiC and saccharin (5 × 10-4 M) has high intensity at all current densities studied.
This is due to the high binding energy of the atoms on the surface and the total energy involved in the structure. In these conditions the material is electrochemically less active.
386
Zulema A. Mahmud et al. / Procedia Materials Science 9 (2015) 377 – 386
4. Conclusion
x Alumina or silicon carbide particles incorporated in the Ni-Zn coating modify the corrosion resistance of the material. This is because the presence of alumina or SiC particles increases the percentage of Ni in the alloy.
x The hardness of the material increases in the presence of both types of particles in the Ni-Zn. The material thickness influences the quality of the material.
x There is an optimum thickness of 10 μm in which ZnNi with CSi reinforces J (3,3,0) textures and changes to K(1,1,0) phase in ZnNi with Al2O3.
x The analysis of operation variables to obtain the material has shown that using a current density electrolysis of 8 A/dm2 for 10 minutes and an adequate concentration in the component of bath and controlled stirring a material with better barrier properties and microstructure is achieved in the presence of particles and saccharine additive.
References
Beltowska and Lehman., 2002. Surface and Coating Technology 151-152, 444. Byk, T. V. Gaevskaya, and L. S. Tsybulskaya., 2008. Effect of electrodeposition conditions on the composition, microstructure, and corrosion
resistance of Zn–Ni alloy coatings. Surf. Coatings Technol., vol. 202, no. 24, pp. 5817–5823. Brooks, I. 1998. Thesis. Characterization of Nanocrystalline Single. Douglas Thomas ; 1985. Corrosion Test”, Electroplating Engineering Handbook. Durney, L.J. 4th ed. 328. Espenhahn, M., 1992. 2nd International Conference on Zinc and Zinc Alloy Coated Steel Sheet; Galvatech 92,273. Fratesi, R. Roventi, G.,1996. Corrosion resistance of Zn-Ni alloy coatings in industrial production, vol. 82, pp. 158–164. Ichida, T., 1995. 3rd International Conference on Zinc and Zinc Alloy Coated Steel Sheet; Galvatech 95, 359. Mahmud, Z., 2009. Efecto de los aditivos en el desempeño de los recubrimientos de ZnNi. SAM. Asoc. Argentina Mater. Regist. N° ISSN 1668-
4788, vol. 6 N° 1, pp. 5–11. Mahmud, Z., 2010. Influencia de los aditivos utilizados en el cincado en medio ácido. Thesis. Universidad de Buenos Aires, FCEN-UBA. pp323. Mahmud, Z. A. Pina, J. Mingolo N. Gassa, L. Gordillo, J. 2010. RECUBRIMIENTO CONSTITUÍDO DE UNA ALEACIÓN DE ZnNi MÁS
PARTÍCULAS CERÁMICAS DE CARBURO DE SILICIO Ó ALÚMINA. In Encuentro de Primavera INTI. Mahmud, Z., 2011. Efecto del agregado de alúmina en la calidad del recubrimiento de aleación de Zinc Níquel in Congreso Internacional de
Materiales- CIM – Colombia. Mahmud Z. Paulo T. Gordillo, J. M. N. 2012. Efecto del agregado de partículas cerámicas en la composición de la aleación de Zinc Niquel. In
XX Congresso da Sociedade Iberoamericana de Electroquímica (pp. 2–3). Mahmud, Z., 2013. New material comprising a Zn metal matrix and ceramic particles having very good mechanical properties and high corrosion
resistance Alumina incorporated steel, in EUROMAT 2013- European Congress and Exhibition on Materials in Sevilla-2013. Mosavat, S H, Bahrololoom, M E, Shariat, M H. 2011. Applied Surface Science Electrodeposition of nanocrystalline Zn – Ni alloy from alkaline
glycinate bath containing saccharin as additive. Applied Surface Science, Vol 257- 8311-8316. Oniciu, L.., Muresan, L., 1991. Some fundamental aspects of levelling and brightening in metal electrodeposition. Journal of Applied
Electrochemistry 21-565-574. Park and Szpunar. 2000. The microstructural characterization of electrogalvanized zinc-iron and zinc- nickel coatings. Textures and
Microstructures, Vol. 34. pp. 119-146. Printed in Malaysia. Rajagopalan., S.1970. Metal Finishing Vol70- pp52. Schoch , A., 1907. J.Am. Soc., 29- 311. Soepenberg, E., 1992. 2nd International Conference on Zinc and Zinc Alloy Coated Steel Sheet; Galvatech 92, 278. Winand, R. 1994. Electrodeposition of metals and alloys—new results and perspectives. Electrochimica Acta. doi:10.1016/0013-4686(94)E0023-
S.
Ver+/-
