Modeling of Solutionizing and Solute Redistribution in a Co-Cast Bi-Layer Al Alloy System
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FOR many industrial applications, the required properties for the surface of a part are different from those of the core. As monolithic materials do not usually provide the desired properties for both the surface and the core, surface modification processes are applied to improve the surface properties. Cladding is a surface modification process that has been used for many years to enhance properties such as corrosion resistance, whereas the core alloy retains its desired engineering properties.[1,2] Cladded aluminum alloys have been generally produced via roll bonding, where the clad layer is bonded to the core alloy by rolling the two layers under a certain level of pressure and usually at an increased temperature in a complex multistep process.[2] This process requires a high level of cleanliness at the surfaces before bonding in addition to preheating the clad and core layers, scalping, and edge trimming. It is also a difficult process to apply to some products, particularly those with single-sided clad alloys, combinations where there is a significant difference between the yield strengths of the clad and core alloys, or combinations with varying surface friction characteristics, which cause difficulties during hot rolling.[3] To overcome such challenges, a new process has been introduced by Novelis Inc. (Fusion co-casting technology[4]; Novelis, Inc., Atlanta, GA), which produces cladded/laminated alloys by the direct chill casting process. This technology can produce multilayered and multialloyed ingots with defect-free metallurgical EHSAN FOROOZMEHR, formerly Postdoctoral Fellow, with the Department of Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo, ON, Canada N2L 3G1, is now Assistant Professor, with the Department of Mechanical Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran. SHAHRZAD ESMAEILI, Associate Professor, is with the Department of Mechanical and Mechatronics Engineering, University of Waterloo. Contact e-mail: [email protected] DAVID J. LLOYD, Consultant, and MARK GALLERNEAULT, Technical Director, are with the Novelis Global Technology Centre, Novelis Inc., Kingston, ON, Canada K2L 5L9. Manuscript submitted January 20, 2011. Article published online February 3, 2012 1770—VOLUME 43A, JUNE 2012
bonded interfaces between alloy layers.[5] The ingots can then be processed thermomechanically to achieve laminated sheets. For applications such as automotive sheets with heat-treatable alloy cores, the final gauge sheets should also undergo a solution treatment process to achieve age-hardening capability. As expected, a solution treatment would cause dissolution of certain dispersed phases. In addition, the compositional gradient in the laminated sheet would induce chemical potential gradients and thus diffusion of solutes across the alloy layers. The extent of dissolution and solute redistribution processes would depend on the solution treatment timetemperature profiles. As in the case of a diffusion couple, with enough time at high temperatures, the lamin
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