Mechanical Behavior of Cu/Al multilayers fabricated by Accumulative Roll-Bonding (ARB) processing
Chemical and Materials Engineering
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For many years, there have been long-standing interests in studying multilayer metals. And many kinds of multilayers are fabricated via a variety of methods. Recently, in an effort to obtain ultrafine grains, a novel technique, namely, accumulative roll-bonding (ARB) is created, which is a kind of severe plastic deformation (SPD) process . Via this technique extremely high strain can be obtained when metal materials are processed; and the properties of original metals can also be largely changed. However, ARB process is rarely applied to multilayer fabrication, especially the fabrication of multilayer bimetals. This thesis focuses on how to obtain Al/Cu multilayers via ARB process, and also examines the microstructure evolution with the increasing number of layers, and the metal properties of the obtained multilayers. This thesis first reviews the development and mechanism of rolling, one of the most important metal forming processes, and the application of rolling in metal fabrication in recent years. Then the formation and the development of ARB process are introduced, followed by current studies on ARB process. Among all the methods of fabricating multilayers, ARB process features high efficiency and continuous production of sheet materials, etc., because it is based on the rolling principle. This thesis examines a mass of unique metal properties and the microstructure of the products that experienced ARB process. In this research，a great numbers of conditions for the roll-bonding of aluminum and copper sheets were studied. Besides, aluminum and copper sheets were rolled to 1.1 mm, 0.8 mm, 0.58 mm and 0.5 mm thick as initial samples. Then the Al/Cu multilayer sheets experienced ARB process for up to 10 cycles at most, at various heat treatment temperatures under various annealing conditions, with various reductions in thickness per cycles and different thickness ratio of aluminum and copper layers. Altogether 11 groups were obtained. In this thesis, the samples in 4 groups of them were investigated. The ARB-processed samples in each cycle of the selected groups were cut off a little piece to study the microstructure evolution and micro hardness. Some aluminum alloy was found during the process, which increased in amount as the number of cycles increased. Up to 7 cycles, the amount of al-alloy increased tremendously and as a result the properties and microstructures were largely changed. This will be discussed in details in Chapter 4.