Influence of Constituent Materials on the Impact Toughness and Fracture Mechanisms of Hot-Roll-Bonded Aluminum Multilaye
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TRODUCTION
IN recent years, metallic multilayer composites have received attention due to their striking mechanical, electrical, and magnetic characteristics.[1,2] Through an adequate design of these structures and taking into account the responsible mechanisms of the improved failure behavior as compared to those of the individual components, it is possible to tailor materials to the requirements of a particular application.[3] The most common method used in industry to manufacture these laminates is roll bonding. In this process, two or more strips of similar or dissimilar alloys are rolled together for several passes.[4–6] The rolling process is capable of producing the high interfacial pressures required to cause strong adhesion of the components by complex interface development.[7] A metallurgical bond between the alloys then develops at the interface during the rolling process. Furthermore, the bond quality is influenced by a number of interdependent parameters such as temperature, pressure (determined by the degree of reduction), contact time (roll speed),[8] and the mechanical behavior of the constituent materials to be bonded at the processing temperature. Multilayer composite laminates based on aluminum alloys have been developed by hot roll bonding,
resulting in materials of improved impact toughness.[5,9] In hot-rolled aluminum multilayer laminates, bonding occurs by fracturing of the surface alumina on the layers and then flowing the aluminum through the fractured alumina regions. Consequently, the cracking of the alumina coating allows metal-metal contact and roll bonding to take place. The interface, therefore, is a combination of oxide fragments and bonded areas of ‘‘extruded’’ aluminum.[9] In the present work, two multilayer materials based on different constituent aluminum alloys have been processed by hot roll bonding. The Al 2024 alloy and Al 1050 constitute the first of them and the second one is based in a high-strength Al 7075 alloy and Al 1050. The Al 2024 and Al 7075 alloys have been selected due to their high strength and their extensive application in commercial aircrafts. On the other hand, the high ductility of the Al 1050 favors bonding between the aluminum layers during processing. Therefore, the objective of this study is to analyze the influence of the constituent materials on the fracture mechanisms and the improved impact toughness of roll-bonded laminates processed by similar strain paths.
II. C.M. CEPEDA-JIME´NEZ, Ph.D. Researcher, P. HIDALGO, Ph.D. Student, O.A. RUANO, Professor, and F. CARREN˜O, Staff Researcher, are with the Department of Physical Metallurgy, CENIM, CSIC, 28040 Madrid, Spain. Contact e-mail: [email protected] M. POZUELO, Postdoctoral Researcher, is with the Department of Materials Science and Engineering, University of California, Los Angeles, CA 90095-1595. Manuscript submitted May 29, 2009. Article published online October 29, 2009 METALLURGICAL AND MATERIALS TRANSACTIONS A
EXPERIMENTAL PROCEDURE
A. Materials and Processing The aluminum alloys used in th
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