Corrosion evaluation of multi-pass welded nickel–aluminum bronze alloy in 3.5% sodium chloride solution: A restorative application of gas tungsten arc welding process Behnam Sabbaghzadeh a , Reza Parvizi a , Ali Davoodi b,⇑ , Mohammad Hadi Moayed a a Department of Materials and Metallurgical Engineering, Faculty of Engineering, Ferdowsi University of Mashhad, 91775-1111, Iran b Department of Materials and Polymer Engineering, Faculty of Engineering, Hakim Sabzevari University, Sabzevar 391, Iran article info Article history: Received 15 October 2013 Accepted 10 February 2014 Available online 18 February 2014 Keywords: Gas tungsten arc welding Nickel–aluminum bronze Galvanic corrosion EIS abstract In this research, the corrosion behavior of a gas tungsten arc welded nickel–aluminum bronze (NAB) alloy is investigated by DC and AC electrochemical techniques in 3.5% sodium chloride solution. Regarding the electrochemical impedance spectroscopy and potentiodynamic results, uniform corrosion resistance of instantly immersed weld and base samples are almost analogous and increased (more in weld region) during the immersion times. Moreover, zero resistant ammeter results demonstrated that the few nano- ampere galvanic currents are attributed to microstructural and morphological differences between these two regions. Therefore, the welding procedure could not deteriorate the general corrosion resistance of the restored damaged NAB parts operating in marine environments. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Nickel–aluminum bronze (NAB) alloys containing 9–12% (wt.%) aluminum with additions of up to 6% (wt.%) of iron and nickel, rep- resent one of the most important groups of commercial aluminum bronzes. As the major alloying element, aluminum content would result in higher strength and improve the corrosion resistance (by formation of an oxide/hydroxide film) and castings/hot work- ing properties. On the other side, nickel also improves corrosion resistance, strength and stabilises the microstructure while iron refines grains and increases the alloy tensile strength [1,2]. Both cast and wrought aluminum bronze compounds offer a good com- bination of mechanical properties and corrosion resistance. Conse- quently, aluminum bronzes have been widely used for decades in a variety of marine or saline environments including valves, fittings, ship propellers, pump castings, pump shafts, valve stems and heat exchanger water boxes [2–4]. However, these alloys can suffer from localized corrosion (e.g. pitting, crevice, etc.) especially in flow conditions [5]. NAB alloys are metallurgical complex alloys with several intermetallic phases such as a, b 0 , j i , j ii , j iii and j iv in which small variations in composition can result in development of markedly different microstructures. This can also lead to exten- sive changes of alloy corrosion resistance in seawater. The microstructures that can result in an optimum corrosion resistance can be obtained by controlling the composition and the heat treat- ment procedure [1]. Wharton et al. used five types of NAB alloys (as-cast and wrought) with different compositions and heat treat- ment (annealing) backgrounds and compared their corrosion behaviors through various electrochemical techniques [1]. They reported that the cast/annealed samples represented higher corro- sion current densities in compared to wrought samples in seawater [1]. However, NABs are the most corrosion resistant types of copper-based alloys to flow-induced corrosion [5,6]. Their resis- tance has been attributed to a thin protective layer, containing alu- minum and copper oxides [7,8]. Due to the presence of stable intermetallic compounds in NAB and the a/b phase boundary that is near the solidus line, it is very difficult to homogenize these al- loys at their solid state and thus, a welding approach can be per- formed for this aim [9]. Indeed, this is a crucial matter whenever an inevitable industrial assembling process such as welding oper- ation is carried out. Alternatively, some defects and cracks can be induced by cavitation, de-alloying, stress corrosion cracking, pitting and ero- sion–corrosion mechanisms in some parts of NAB alloys (e.g. impellers), after long exposure times to seawater [10–14]. For in- stance, Alfantazi et al. reported that for a couple of copper alloys in 1 M NaCl solution (pH = 6), the samples experienced a general dissolution mechanism at higher overpotentials and did not suffer from localized corrosion while at more alkaline pH conditions, they revealed a type of passivity (and passivity breakdown) behavior in http://dx.doi.org/10.1016/j.matdes.2014.02.019 0261-3069/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel./fax: +98 5714003520. E-mail address: a.davoodi@hsu.ac.ir (A. Davoodi). Materials and Design 58 (2014) 346–356 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes