Microstructural Evolution and Fracture Behavior of Friction-Stir-Welded Al-Cu Laminated Composites
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LAMINATED composites may have better properties than monolithic materials, because laminates incorporate materials with superior mechanical, physical, or chemical characteristics. Laminated composites have extensive use in various industries such as in aerospace, automotive, and chemical plants. Roll bonding is a versatile joining technique and one of the simplest and least expensive methods for producing laminated composites. In the last two decades, a new solid-state welding technique, friction stir welding (FSW), has emerged and is used increasingly for joining many similar and dissimilar metals. FSW reduces the formation of intermetallic compounds and avoids problems associated with melting during fusion welding. The main problems associated with the fusion welding of bilayer composites are the different chemical and physical properties and the affinity of two metals to form intermetallics.[1] To the author’s knowledge, there is no literature about fusion welding of bilayer composites. However, whereas fusion welding of bilayer composites is similar to fusion welding of dissimilar materials, the same problems associated with fusion welding of dissimilar materials such as intermetallic formation[2] are established. Hence, the FSW process can be used to join laminated composites comprised of dissimilar materials. The behavior of laminated composites during FSW differs from that of conventional materials. In laminated composites, the material properties vary through the R. BEYGI, Ph.D. Student, MOHSEN KAZEMINEZHAD, Associate Professor, and A.H. KOKABI, Professor, are with the Department of Materials Science and Engineering, Sharif University of Technology, Tehran, Iran. Contact e-mail: [email protected] Manuscript submitted May 22, 2013. Article published online October 25, 2013 METALLURGICAL AND MATERIALS TRANSACTIONS A
thickness. Thus, it is necessary to consider which layer is in contact with the shoulder of FSW. Moreover, the heat distribution and plastic flow through thickness are not uniform. In spite of versatile applications of laminated composites, there are a few studies on butt joining of these materials in similar or dissimilar conditions. Taendl et al.[3] carried out friction stir butt welding on multilayered steels containing 15 alternating layers of martensitic and austenitic steels. In their study, they investigated the effect of microstructural evolution of layers during welding on mechanical properties of the joint. However, they did not mention the effect of the contact layer on the material flow and mechanical properties of the joint. In the present study, the FSW process is carried out on Al-Cu-laminated composites containing two layers of Al and Cu to establish microstructural evolution and mechanical properties of the joint. Through FSW, butt joining of the Al-Culaminated composite seems similar to lap welding of Al to Cu in the manner of which one material is superimposed on the other during welding. However, it must be considered that in lap welding, the pin penetrates partially in the lowe
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