High-temperature mechanical behavior and hot rolling of AA705X
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I. INTRODUCTION
HIGHLY alloyed aluminum has been one of the most widely successful and broadly applicable materials developed for engineering structures in the last century. Industries that have benefited from the development of these alloys include packaging, automotive, and aerospace. The Al-ZnMg-Cu 7000 series alloys have seen extensive use in the aerospace industry. The 705X alloys, which exhibit both a high fracture toughness and high resistance to stress corrosion cracking when brought to a T7 temper, were specifically developed to be used in plate form for structural wing components in commercial aircraft.[1] Fabrication of these products begins with direct chill casting followed by heat treatment for homogenization. The slabs are then taken from the solution treatment furnace, and hot rolled through several passes until the desired final thickness is achieved. The rolled material is then quenched and stretched. In the final step, the plate is aged to precipitate the strengthening phases. The thermomechanical history in these processes produces through-thickness gradients in constituent phase, and precipitate distributions, texture, and grain structure, which all lead to gradients in mechanical properties. A detailed review and study of the relationship between microstructure, strength, and toughness in aged 7050 plate, with consideration of anisotropy, has been given by Dumont et al.[2] It is desirable to look further upstream and define the thermomechanical processing window (TPW), i.e., the range of physically realizable processing parameters (roll speed, lay-on temperature, reduction, lubricant properties, etc.) that lead to production of a quality product. S.F. HARNISH, formerly with the Department of Mechanical and Industrial Engineering, University of Illinois, is with Gamma Technologies, Inc., Westmont, IL 60559. H.A. PADILLA, J.A. DANTZIG, and A.J. BEAUDOIN are with the Department of Mechanical and Industrial Engineering, University of Illinois, Urbana, IL 61801. B.E. GORE and I.M. ROBERTSON are with the Department of Materials Science and Engineering, University of Illinois. H. WEILAND is Division Manager Material Science, with the Alcoa Technical Center, Alcoa, PA 15069. Manuscript submitted May 20, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS A
To gain a better understanding of the limits of the TPW and what microstructural processes govern the material behavior near those limits, experiments and numerical simulations have been performed. Material characterization studies under different temperature and stress histories provide an understanding of the precipitate and second-phase structure, and indicate active deformation mechanisms. Guided by these results, and industrial practice, a homogenization procedure is developed and used to prepare samples for mechanical testing. A novel test procedure is also introduced, which permits identifying the onset of damage. The mechanical test data are then used to develop constitutive relations appropriate for hot rolling. We pose a rolling model through
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