International Journal of Minerals, Metallurgy and Materials Volume 25, Number 8, August 2018, Page 967 https://doi.org/10.1007/s12613-018-1646-z Corresponding author: Ali Shamsipur E-mail: Shamsipur@aut.ac.ir © University of Science and Technology Beijing and Springer-Verlag GmbH Germany, part of Springer Nature 2018 Improvement of microstructure and corrosion properties of friction stir welded AA5754 by adding Zn interlayer Ali Shamsipur 1) , Amir Anvari 1) , and Ahmad Keyvani 2) 1) Department of Mining and Metallurgical Engineering, Amirkabir University of Technology, Tehran 15875-4413, Iran 2) School of Metallurgy and Materials Engineering, Faculty of Technology and Engineering, Shahrekord University, Shahrekord 8818634141, Iran (Received: 20 January 2018; revised: 10 March 2018; accepted: 20 March 2018) Abstract: This study investigated the effect of Zn foil layers on the microstructure and corrosion characteristics of friction stir welded alu- minum alloy 5754. Samples of various joints were prepared by applying different rotational and welding speeds, and their microstructures were evaluated via a metallographic technique and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy ele- mental analysis. The anticorrosion behavior of joints in the absence and presence of a Zn interlayer was studied by cyclic potentiodynamic polarization test in 3.5wt% NaCl aqueous solution, and sound welds were obtained in the presence of the Zn interlayer foil. The results re- vealed that the joint made at a rotational speed of 800 r/min and traveling speed of 15 mm/min achieved a chemical composition identical to that of aluminum alloy 7xxx series, and as such, it showed the best resistance to corrosion. Keywords: friction stir welding; AA5754 aluminum alloy; zinc interlayer; microstructure; corrosion resistance 1. Introduction Aluminum alloys, as prominent engineering materials, have many industrial applications because of their light weight and high strength [1]. For example, the 2xxx and 7xxx series can be used in aircraft structural parts, and 5xxx and 6xxx series can be used to fabricate automotive parts [2-3]. However, many challenges of manufacturing with aluminum parts, particularly joining methods, need to be well addressed. Over the recent years, there has been an increasing inter- est on novel welding techniques. For instance, friction stir welding (FSW), introduced by The Welding Institute (TWI), UK in 1991, is a solid state joining method that eliminates conventional welding defects such as cracking, gas porosity, and distortion [4]. Meanwhile, much attention has also been focused on joining materials with adherent oxide layers, particularly aluminum alloys [5-7] as well as structural ma- terials with high melting temperatures, such as steels [8-13]. In addition, various studies have been conducted on the joining of various dissimilar metals and alloys by FSW [14]. Several investigations have been dedicated to welding parameters (pin geometry, rotational and traveling speeds, etc.) in FSW of Al alloys [15-24], and it has been discov- ered that the ratio of rotational speed to traveling speed is important in determining the mechanical properties of a joint [25-26]. In addition, many attempts have been imple- mented to add precipitating particles to the joint gaps to achieve composite weld zones [27-29]. More recently, the joint properties have been improved by adding an intermediate layer, which can be in forms of sheet, filler, or foil [30-32]. In a study by Xu et al. [33] on dissimilar joint between aluminum 5754 and high strength steel, a layer was coated on steel to control the formation of brittle intermetallic compounds. They fabricated a friction stir spot welded Mg-Zn-Al alloy by adding zinc (Zn) inter- layer and reported a reduction of weld defects. In this study, we investigated the effect of Zn foil insert on friction stir welded 5754 joints and assess the microstructural changes and corrosion behaviors. 2. Experimental A 4 mm aluminum H114-5754 sheet of 100 mm × 200 mm with the chemical composition presented in Table 1 was