Materials Science and Engineering B 148 (2008) 82–87 Friction stir welding of dissimilar AA2024 and AA7075 aluminum alloys Saad Ahmed Khodir ∗,1 , Toshiya Shibayanagi Joining and Welding Research Institute, Osaka University, 11-1, Mihogaoka, Ibaraki, Osaka 567-0047, Japan Received 22 May 2007; received in revised form 25 August 2007; accepted 3 September 2007 Abstract The present study focuses on the microstructure and mechanical properties of dissimilar joints of 2024-T3 Al alloy to 7075-T6 Al alloy produced by friction stir welding. Effects of welding speed and fixed location of base metals on microstructures, hardness distributions, and tensile properties of the welded joints were investigated. SEM-EDS analysis revealed that the stir zone contains a mixed structure and onion ring pattern with a periodic change of grain size as well as a heterogeneous distribution of alloying elements. The maximum tensile strength of 423.0 MPa was achieved for the joint produced at welding speed of 1.67 mm/s when 2024 Al alloy was located on the advancing side. © 2007 Elsevier B.V. All rights reserved. Keywords: Friction stir welding; 2024-T3 Al alloy; 7075-T6 Al alloy; Welding speed; Microstructure; Mechanical properties 1. Introduction Friction stir welding (FSW) is a solid-state joining process invented at The Welding Institute (UK) in 1991 [1,2]. The joint- ing process proceeds in a solid-state where temperature during welding is relatively less than the melting point of welded metal [3–5]. The heat generation caused by the friction between the welding tool and weld metal makes the surrounding material around the tool is soft and allows the tool to move along the joint line [5]. Dissimilar joints of 2024-T3 to7075-T6 Al alloys are required for aerospace application to optimize mechanical and chemical properties. Although, there are some previous reports about dissimi- lar joining of 2024-T3 to 7075-T6 Al alloys [6,7], there is no information about the effect of welding conditions on the microstructure and mechanical properties of butt welded joints. The present study aims to investigate the effects of welding speed and fixed location of material on microstructure, hardness distribution, and tensile properties for dissimilar of 2024-T3 to 7075-T6 Al alloys joints produced by FSW. ∗ Corresponding author. E-mail address: saad@jwri.osaka-u.ac.jp (S.A. Khodir). 1 Graduate Student of Osaka University, Japan. 2. Experimental procedures Plates 3 mm thick of 2024-T3 and 7075-T6 Al alloys were friction stir butt welded using a tool (SKD61) composed of 12 mm diameter shoulder and 4.0 mm diameter threaded pin. Chemical compositions in mass% of base metals (BMs) 2024 and 7075 Al alloys are 5.35Cu, 0.67Mn, 2.7Mg, Al balance and 7.99Zn, 2.52Mg, 2.4Cu, 0.1Mn, Al balance, respec- tively. Mechanical properties at room temperature of the BMs are shown in Table 1. Rotation speed was kept constant at 20 s -1 and welding speed was set at 0.7, 1.2, 1.7 and 3.3 mm/s. Microstructures of various regions of welds were observed in the cross-section of the joint by optical microscopy. The homogeneity of constituents in the stir zone (SZ) was ana- lyzed by SEM-EDS method. Microhardness measurement was carried out 4.3 Ms (50 days) after natural aging. The ten- sile test was carried out at room temperature at a strain rate of 1.2 × 10 -3 s -1 . 3. Results and discussion 3.1. Macro and microstructures of joints Macroscopic appearances of the cross-section of the joints produced at a rotation speed of 20 s -1 and welding speeds of 0921-5107/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2007.09.024