Dissimilar friction welding of 6061-T6 aluminum and AISI 1018 steel: Properties and microstructural characterization Emel Taban a, * , Jerry E. Gould b , John C. Lippold c a Kocaeli University, Engineering Faculty, Dept. of Mechanical Engineering, Kocaeli 41380, Turkey b Edison Welding Institute, Edison Joining and Technology Center, Columbus, OH 43221, USA c The Ohio State University, Dept. of Integrated Systems Engineering, Welding Eng. Program, Columbus, OH 43221, USA article info Article history: Received 26 October 2009 Accepted 4 December 2009 Available online 11 December 2009 Keywords: Dissimilar welding Aluminum Steel Microstructural characterization abstract Joining of dissimilar materials is of increasing interest for a wide range of industrial applications. The automotive industry, in particular, views dissimilar materials joining as a gateway for the implementa- tion of lightweight materials. Specifically, the introduction of aluminum alloy parts into a steel car body requires the development of reliable, efficient and economic joining processes. Since aluminum and steel demonstrate different physical, mechanical and metallurgical properties, identification of proper welding processes and practices can be problematic. In this work, inertia friction welding has been used to create joints between a 6061-T6 aluminum alloy and a AISI 1018 steel using various parameters. The joints were evaluated by mechanical testing and metallurgical analysis. Microstructural analyses were done using metallography, microhardness testing, scanning electron microscopy (SEM), energy dispersive spectros- copy (EDS), X-ray elemental mapping, focused ion beam (FIB) with ultra high resolution SEM and trans- mission electron microscopy (TEM) in TEM and STEM modes. Results of these analysis first suggested that joint strengths on the order of 250 MPa could be achieved. In addition, failures were seen in the plasti- cized layer on the aluminum side of the joint. Further, bond lines were characterized by a thin layer of formed Al–Fe intermetallic. This intermetallic layer averaged roughly 250 nm thick and compositionally appears related to the FeAl and Fe 2 Al 5 phases. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Dissimilar metal joining offers the potential to utilize the advantages of different materials often providing unique solutions to engineering requirements. The main reasons for dissimilar join- ing are due to the combination of good mechanical properties of one material and either low specific weight or good corrosion resistance or good electrical properties of second material. Conse- quently, joining processes for dissimilar materials have received considerable attention in the recent years. Much of this activity has focused on the transportation industries such as aerospace, aviation, shipbuilding, railway transportation. This is especially in the automotive industry due to the potential weight reduction of both vehicle components and structures. The need to expand the use of lightweight structures in the automotive industry has in- creased interest in the use of both aluminum and magnesium as structural materials. However, the cost of aluminum compared to steel restricts its application for automobile parts. As a result alu- minum is more economical when it can be used in hybrid struc- tures with steel. In order to incorporate these hybrid structures, proper joining methods for aluminum-to-steel dissimilar combina- tions are necessary. Steel and aluminum have been successfully joined for production applications using both mechanical fastening and adhesive bonding. Although these approaches have demon- strated fitness for the intended applications, they suffer from low specific strengths and are largely limited to lap geometries. In con- sidering structural joints between steel and aluminum, welding processes should be taken into account [1–10]. Research conducted on the welding of aluminum to steel ranges from solid state to fusion welding processes. Specific processes investigated include as resistance spot [4–12], friction stir [3,13– 15], friction stir knead [16], friction stir spot [17–19], diffusion [20], magnetic pulse [21,22], magnetic pressure seam [23], electro- magnetic impact [24], and explosion welding processes [25,26], and gas metal arc welding (GMA)–cold metal transfer (CMT) [27], laser beam [28–31], laser assisted pressure [32], laser hybrid [33], laser roll [34], and braze assisted [35–37] welding processes. Mechanical bonding between steel and aluminum is challenged due to significant differences in both physical and metallurgical properties. For example, large differences in thermal properties such as expansion coefficient, conductivity, and specific heat can lead to residual stresses. Metallurgically, joints between aluminum and steel can result in multiple intermetallic phases that generally 0261-3069/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2009.12.010 * Corresponding author. Tel.: +90 2623033405; fax: +90 2623352880. E-mail addresses: emel.taban@yahoo.com, taban.1@osu.edu (E. Taban). Materials and Design 31 (2010) 2305–2311 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes