The tensile response of a fine-grained AA5754 alloy produced by asymmetric rolling and annealing
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2/20/04
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The Tensile Response of a Fine-Grained AA5754 Alloy Produced by Asymmetric Rolling and Annealing H. JIN and D.J. LLOYD Asymmetric rolling (ASR) followed by annealing has been used to produce very fine grain sizes in the commercial Al-3 wt pct Mg alloy, AA5754. The appropriate rolling and annealing practice can produce grain sizes as small as 1 m, and the tensile response of this fine-grained material has been compared with that of other fine-grained alloys produced by alternative methods. It is shown that the material obeys a Hall–Petch relationship, with a slope very similar to that of AA5754 produced by equal-channel angular extrusion (ECAE) and by conventional hot and cold rolling. The high yield strengths at fine grain sizes are accompanied by a low tensile elongation, which reflects the stress-strain response of very fine grain sizes. The stress-strain response can be described by the Voce equation, with the dislocation-accumulation rate decreasing with decreasing grain size and the rate of dynamic recovery being controlled by the Mg solute. Tensile elongations generally decrease with decreasing grain size, but a duplex grain structure appears to provide a good compromise between strength and elongation.
I. INTRODUCTION
MANIPULATION of grain size is one of the important methods of influencing the strength and mechanical response of many metals and alloys, and the control of grain size is often achieved by suitable combinations of cold work and annealing. Various techniques have been developed to produce severe plastic deformation and, hence, the levels of stored energy required to produce fine-grained structures.[1,2] These methods include equal-channel angular extrusion (ECAE),[3] high-pressure torsion,[4] and accumulated roll bonding,[5] but all have limitations on the dimensions of the material that can be easily produced. An interesting alternative method which may be more compatible with the required scale of structural materials, and conventional fabrication processes, is asymmetric rolling (ASR),[6,7] in which sheet is rolled between rolls that are either of different diameters, or are rotating at different speeds. Under these circumstances, the material is subjected to enhanced shear deformation, and it has been suggested that high-angle boundaries develop with increasing strain, and ultrafine grains are formed by continuous recrystallization on annealing. In the present article, ASR has been used to develop ultrafine grain sizes in AA5754 sheet, and the tensile response of the fine-grained sheet was investigated. II. EXPERIMENTAL The material used in this work was an AA5754 sheet with a chemical composition of Al-3.08Mg-0.26Mn-0.19Fe-0.06Si (wt pct). The sheet was annealed at 400 °C for 4 hours, then conventionally rolled from 28.3 mm in thickness down to 7.6 mm. Afterwards, one section was interannealed at 330 °C for 10.5 hours then asymmetrically cold rolled down to a final gage of 1.1 mm, while another section was directly H. JIN, Research Scientist, and D.J. LLOYD,
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