  Citation: Ghiasvand, A.; Suksatan, W.; Tomków,J.; Rogalski, G.; Derazkola, H.A. Investigation of the Effects of Tool Positioning Factors on Peak Temperature in Dissimilar Friction Stir Welding of AA6061-T6 and AA7075-T6 Aluminum Alloys. Materials 2022, 15, 702. https:// doi.org/10.3390/ma15030702 Academic Editors: Eduardo Garcia, Alberto Murillo-Marrodán and Hamed Aghajani Derazkola Received: 27 December 2021 Accepted: 13 January 2022 Published: 18 January 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). materials Article Investigation of the Effects of Tool Positioning Factors on Peak Temperature in Dissimilar Friction Stir Welding of AA6061-T6 and AA7075-T6 Aluminum Alloys Amir Ghiasvand 1 , Wanich Suksatan 2 , Jacek Tomków 3 , Grzegorz Rogalski 3 and Hesamoddin Aghajani Derazkola 4, * 1 Department of Mechanical Engineering, University of Tabriz, Tabriz 5166616471, Iran; amir.ghiasvand@tabrizu.ac.ir 2 Faculty of Nursing, HRH Princess Chulabhorn College of Medical Science, Chulabhorn Royal Academy, Bangkok 10210, Thailand; wanich.suk@pccms.ac.th 3 Institute of Manufacturing and Materials Technology, Faculty of Mechanical Engineering and Ship Technology, Gda´ nsk University of Technology, Gabriela Narutowicza Street 11/12, 80-233 Gda´ nsk, Poland; jacek.tomkow@pg.edu.pl (J.T.); grzegorz.rogalski@pg.edu.pl (G.R.) 4 Department of Mechanical Engineering, Islamic Azad University of Nour Branch, Nour 21655432, Iran * Correspondence: h.aghajany@live.com Abstract: Among the emerging new welding techniques, friction stir welding (FSW) is used frequently for welding high-strength aluminum alloys that are difficult to weld by conventional fusion-welding techniques. This paper investigated the effects of tool-positioning factors on the maximum tem- perature generated in the dissimilar FSW joint of AA6061-T6 and AA7075-T6 aluminum alloys. Three factors of plunge depth, tool offset, and tilt angle were used as the input parameters. Nu- merical simulation of the FSW process was performed in ABAQUS software using the coupled Eulerian–Lagrangian (CEL) approach. Central composite design (CCD) based on response surface methodology (RSM) was used to analyze and design the experiments. Comparison of the numeri- cal and experimental results showed that numerical simulations were in good agreement with the experimental ones. Based on the statistical model results, plunge depth, tilt angle, and tool offset were the most significant factors on maximum process temperature, respectively. It was found that increasing the plunge depth caused a sharp increase in the maximum process temperature due to increased contact surfaces and the frictional interaction between the tool and workpiece. Keywords: friction stir welding (FSW); tool offset; tilt angle; plunge depth; maximum process temperature 1. Introduction Friction stir welding (FSW) was one of the relatively novel welding techniques in- vented at The Welding Institute (TWI) in the UK in 1991 [1,2]. This process is categorized into a group of welding processes called solid-state bonding techniques [3]. The FSW joint is formed using a non-consumable tool that plunges into the workpiece and translates along the weld line [4,5]. Unlike other conventional welding processes, this technique does not need any filler materials, and the tool retracts from the workpiece after welding formation [6]. The main factors in producing an appropriate and defect-less joint are heat generation and its proper distribution into the welding zones [7]. To achieve the best conditions to form an adequate plastic flow, the maximum temperature created in the weld nugget should be in the range of 0.8 to 0.9 of the melting temperatures of involved materials in the joint [8]. In the FSW process, total heat is generated by two factors: severe friction between tool and workpiece and material flow created during the joint formation [9]. Based on the literature, a significant portion of generated heat belongs to the frictional condition between tool and workpiece, and the rest is related to plastic flow [10,11]. Due Materials 2022, 15, 702. https://doi.org/10.3390/ma15030702 https://www.mdpi.com/journal/materials