Journal of Alloys and Compounds 513 (2012) 449–454 Contents lists available at SciVerse ScienceDirect Journal of Alloys and Compounds jou rn al h om epage: www.elsevier.com/locate/jallcom Comparative study on structure, corrosion and hardness of Zn–Ni alloy deposition on AISI 347 steel aircraft material RM. Gnanamuthu a , S. Mohan b,∗ , G. Saravanan b , Chang Woo Lee a,∗ a Department of Chemical Engineering, College of Engineering, Kyung Hee University, 1732 Deogyeong-daero, Gihung, Yongin, Gyeonggi 446-701, South Korea b Central Electrochemical Research Institute, (CSIR), Karaikudi 630 006, Tamilnadu, India a r t i c l e i n f o Article history: Received 23 August 2011 Received in revised form 20 October 2011 Accepted 22 October 2011 Available online 7 November 2011 Keywords: Metals and alloys Corrosion: Electrochemical reactions: Pulse plating AFM a b s t r a c t Zn–Ni alloys were electrodeposited on AISI 347 steel aircraft materials from various electrolytes under direct current (DCD) and pulsed electrodepositing (PED) techniques. The effects of pulse duty cycle on thickness, current efficiency and hardness of electrodeposits were studied. Alloy phases of the Zn–Ni were indexed by X-ray diffraction (XRD) techniques. Microstructural morphology, topography and elemental compositions were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray fluorescence spectroscopy (XRF). The corrosion resistance properties of electrode- posited Zn–Ni alloy in 3.5% NaCl aqueous solution obtained by DCD and PED were compared using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) technique. Elemen- tal analysis showed that 88% of Zn and 12% of Ni obtained from electrolyte-4 by PED technique at 40% duty cycle for 50 Hz frequencies having better corrosion resistance than that of deposits obtained from other electrolytes. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Electrodeposited Zn–Ni alloy provides an excellent corrosion resistance for steel in relatively aggressive environments. Recently Zn–Ni alloys have received more interest than other alloys [1,2] because of more negative than Fe and dissolve rapidly in highly corrosive environments. Nickel-based alloys are used in a wide variety of applications for aerospace, energy generation and corro- sion protection, especially in an environment where materials have to withstand high temperatures and oxidizing conditions. Zn–Ni alloy electrodeposition was carried out in a sulfamate bath by pulse plating [3]. Zn–Ni alloy coatings were carried out by direct current (DC), pulse current (PC) and pulse reverse current (PRC) methods in a sulfate bath [4]. Ramanauskas et al. studied the effects of the pulse parameters on the surface morphology, grain size and cor- rosion properties of Zn–Ni alloy coatings. Compared with coatings deposited by DC plating, the grain size became smaller, the coat- ing surface became denser and smoother, the crystal grains evenly distributed and the number of lattice lacuna also increased, which led to the improvement of the corrosion resistance in a ZnO bath [5]. The structure morphology of electrodeposited Zn–Ni alloy is fine grained than that of a Zn electrodeposits. A nanocrystalline ∗ Corresponding authors. Tel.: +82 31 201 3825; fax: +82 31 204 8114. E-mail addresses: sanjnamohan@yahoo.com (S. Mohan), cwlee@khu.ac.kr (C.W. Lee). Zn–Ni coating can be obtained from an ammonium chloride and chloride based electrolytes [6,7]. Although alkaline Zn–Ni electro- plating has been successfully developed, there are no unambiguous reports regarding the nanocrystalline Zn–Ni coating obtained from an alkaline bath. Particularly Zn–Ni alloys owing to their excellent corrosion resistance behaviour in saline environments. The mechanism for electrodeposition of Zn–Ni alloys in NH 4 Cl electrolyte is the formation of mixed intermediate surface com- pound (ZnNi + ads ) adsorbed at cathode surface is shown in Eq. (2) [8]. (ZnNi + ads ) + e - → Zn + Ni (1) Also, Hadian and Gabe reported that pulse plating mode could reduce the residual stress of the alloy coatings in a certain degree [9]. The properties of alloy coatings greatly depend on the structure and the composition [10]. Due to be favor of resolving many prob- lems of the direct current (DC) plating, these techniques present the promising prospects in the inexpensive metal plating field [11]. However, there are only a few instances of the research on Zn–Ni alloy coating by PC and PRC plating technique reported at present. The present work demonstrates the structure, hardness and cor- rosion properties of Zn–Ni alloy and Zn on AISI 347 stainless steel aircraft materials under direct and pulsed current techniques using various electrolytes. 0925-8388/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2011.10.078