Microstructure and Microtexture Formation of AZ91D Magnesium Alloys Solidified in a Static Magnetic Field

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better performance of an alloy in engineering, it is of great importance to control the microstructure and microtexture that play a vital role in inﬂuencing the material properties. Thanks to the rapid development of superconducting magnet technologies, the past two decades have witnessed a signiﬁcant progress in processing materials in a high magnetic ﬁeld and various techniques have been developed to produce novel microstructures and microtextures, e.g., the electromagnetic separation of inclusions,[1] ceramics sintering,[2,3] ﬁlm deposition,[4] and the recrystallization of amorphous alloys.[5] Because of the anisotropy in crystalline lattice, diﬀerent crystal planes have diﬀerent magnetic susceptibilities, i.e., diﬀerent levels of magnetization for crystal planes in response to an applied magnetic ﬁeld. It is the anisotropy in the magnetic susceptibility that yields the magnetic torque in a static magnetic ﬁeld and thus drives a crystal to align along its preferential MINGJUN LI and TAKUYA TAMURA, Researchers, and KENJI MIWA, Group Leader, are with the Materials Research Institute for Sustainable Development, National Institute of Advanced Industrial Science and Technology (AIST), Aichi-ken, 463-8560 Japan. Contact e-mail: [email protected] Manuscript submitted July 31, 2008. Article published online April 14, 2009 1422—VOLUME 40A, JUNE 2009

orientation, by which the magnetization energy can be minimized. The earliest experiment using this principle in solidiﬁcation may be due to Rango et al.,[6] who solidiﬁed the YBa2Cu3O7 superconducting oxide in a static magnetic ﬁeld and found a well-aligned texture. Following this approach, several alloys have been solidiﬁed to examine the inﬂuence of the static magnetic ﬁeld on texture formation, e.g., Sm2Co17,[7] Bi-20 at. pct Mn,[8] Al-10 at. pct In,[9] Sn-Pb,[10] and (TbDy)Fe2[11,12] alloys, revealing that the solidiﬁed crystals can be well aligned to preferential planes when the magnetic ﬂux density exceeds a critical value. Very recently, Asai[13] reviewed the alignment of crystalline phase in a static magnetic ﬁeld, including solidiﬁcation and sintering. When an alloy is remelted and solidiﬁed in a crucible, the microstructure of the ingot can be categorized into three zones.[14] The aforementioned studies mainly focused on the inﬂuence of a static magnetic ﬁeld on the inner equiaxed zone. A comprehensive examination of the inﬂuence of a static magnetic ﬁeld on the microstructure and microtexture formation in three zones is still absent. Moreover, increasing applications of the AZ91D (with a nominal composition of Mg-9 wt pct Al-1 wt pct Zn for diecasting) alloy have been found in industry in recent years. However, to our knowledge, there have been no reports on the inﬂuence of a static magnetic ﬁeld on microstructure and microtexture formation for the AZ91D alloy during solidiﬁcation. METALLURGICAL AND MATERIALS TRANSACTIONS A

Because the alloy is magnesium based with a hcp structure that may generate magnetic anisotropic susceptibilities between the c axis and

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