Texture and grain-boundary evolutions of continuous cast and direct chill cast AA 5052 aluminum alloy during cold rollin
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COMPARED with aluminum alloy sheet made by conventional direct chill (DC) cast ingots, aluminum alloy sheet made by using continuous cast (CC) technology possesses advantages of both energy and economic savings while reducing environmental emissions that have become an urgent issue in today’s world. However, there exist substantial differences in the microstructures of CC and DC materials as a result of the difference in the casting processes. The cast structures are almost completely broken up in DC material by extensive thermomechanical processes such as homogenization and hot rolling in reversing mills. After hot rolling, the DC hot band has a uniform distribution of the constituent particles and other precipitates that develop in the solid state. In contrast, the CC material reaches the final stage directly from the cast state without any homogenization or significant degrees of hot working. As a result, CC hot band has a banded intermetallic structure in which the spatial distribution of the particles is not uniform. This situation leads to different recrystallization and texture behaviors and therefore different mechanical properties in the various temper conditions of the two materials. Usually, the formability of CC material is inferior to DC material. AA 5052 is one of the AA 5XXX aluminum alloys that finds a variety of applications in the automotive industry because it lowers the vehicle weight and hence is beneficial for fuel economy. Previous research on AA 5052 alloy has addressed the texture evolution during either hot rolling[1,2] JIANTAO LIU, Graduate Student (Ph.D. Candidate), and JAMES G. MORRIS, Professor of Metallurgical Engineering, are with the Department of Chemical and Materials Engineering, University of Kentucky, Lexington, KY 40506-0046. Contact e-mail: [email protected] Manuscript submitted April 15, 2002. METALLURGICAL AND MATERIALS TRANSACTIONS A
or cold rolling,[3] formability,[4] and earing behavior.[5,6] However, little attention has been paid to the differences in cold rolling texture evolution between CC and DC AA 5052 alloy. The differences could be strongly related to different formability characteristics between CC and DC aluminum alloys. The aim of this study is twofold. First, the cold rolling texture evolution of both CC and DC AA 5052 alloy will be traced and the differences will be highlighted. Second, the grain-boundary evolution of both materials during the early stages of cold rolling (ⱕ40 pct thickness reduction) will be examined and compared.
II. EXPERIMENTAL A. Materials and Procedures The materials used in this work were commercially produced hot bands of CC and DC AA 5052 alloy. The chemical compositions are given in Table I. Plates of 3.7 ⫻ 101.6 ⫻ 127.0 mm3 were cut from the DC hot band and plates of 4.1 ⫻ 101.6 ⫻ 127.0 mm3 from the CC hot band. The cut plates were then annealed at 550 °C for 2 hours followed by water quenching in order to generate a completely recrystallized microstructure before cold rolling. The quenched plates were homogeneously cold rolle
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