Texture weakening of AZ31 magnesium alloy sheet obtained by a combination of bidirectional cyclic bending at low tempera
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Texture weakening of AZ31 magnesium alloy sheet obtained by a combination of bidirectional cyclic bending at low temperature and static recrystallization Qinghuan Huo • Xuyue Yang • Jijun Ma Huan Sun • Jun Wang • Lei Zhang
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Received: 4 July 2012 / Accepted: 16 August 2012 / Published online: 30 August 2012 Ó Springer Science+Business Media, LLC 2012
Abstract In this work, the grain refinement and texture weakening in the sheets of AZ31 magnesium alloy were studied by means of bidirectional cyclic bending for 6 passes at 423 K and subsequent static recrystallization (SRX) on two annealing conditions. The deformed and annealed samples were examined by optical microscopy and electron backscatter diffraction analysis. The results showed that a gradient structure with fine grains in the regions near the surfaces and, in contrast, coarse grains in the middle of the sheet were induced. The texture of the annealed samples was dramatically weakened, and the intensity decreased gradually from the center of the sheet to two surfaces. The different SRX mechanisms significantly affected the different weakening for the basal texture. The cumulative strain energy achieved by twinning played a more important role in the formation of an asymmetric gradient texture intensity distribution after annealing at 523 K for 1000 s. On the contrary, thermal energy dominated a symmetric gradient under annealing at 573 K for 100 s because of the preferential growth of new grains produced by SRX. The ductility is enhanced outstandingly with no remarkable improvement for the strength.
Introduction In order to satisfy the requirements of the lightest structural materials currently, magnesium (Mg) and its alloys have been attracted for their excellent specific properties [1–3].
Q. Huo X. Yang (&) J. Ma H. Sun J. Wang L. Zhang Educational Key Laboratory of Nonferrous Metal Materials Science and Engineering, School of Materials Science and Engineering, Central South University, Changsha 410083, China e-mail: [email protected]
However, their widespread application is restricted because of their hexagonal close-packed (hcp) structure [4–6]. For conventional hot-rolled Mg alloy sheets, the strong basal texture limits their formability seriously. Common deformation or annealing methods cannot weaken the basal texture or make it dispersed [6–8]. Thus, some special deformation techniques have been carried out recently on Mg alloy sheets to control texture. Chino et al. [9, 10] improved the ductility and reduced the anisotropy of AZ31 Mg alloy sheet by cross-roll rolling. Cheng et al. [11] used equal channel angular rolling (ECAR) to compel grains to rotate away from the (0002) orientation. Nevertheless, these methods are not appropriate for manufacturing large parts. Differential speed rolling (DSR) [12–14] has great potential for industrial needs. The authors enhanced the formability by unidirectional shear bands penetrating throughout the thickness of the sheet after DSR with subsequent annealing. The basal pole splits at a large
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