National Research Center for Magnesium Alloys

Chongqing, China

National Research Center for Magnesium Alloys

Chongqing, China
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Zhang D.,Chongqing University | Zhang D.,National Research Center for Magnesium Alloys | Qi F.,Chongqing University | Qi F.,National Research Center for Magnesium Alloys | And 4 more authors.
Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering | Year: 2010

By observing the microstructures and measuring mechanical properties of three kinds of Mg-6Zn-XMn wrought magnesium alloys, the effects of Mn content on microstructures and mechanical properties of Mg-Zn-Mn magnesium alloy was studied. The results show that Mn element distributes dispersively in the matrix mainly as pure Mn particles which can hamper the grain growth, i. e. the grains become finer with Mn content increasing. Mn content has a certain impact on the yield strength of the three alloys, that is, the yield strength increases with Mn content increasing, and the increment of the extruded and the two-stage aged alloys are 14% and 5%, respectively. On the other hand, Mn content has no obvious effect on the tensile strength and elongation of T6 and T4+2-stage aged alloys. The alloy with 0.68wt% Mn after two-stage aging has better overall mechanical properties, whose tensile strength is the highest, 360 MPa, and whose elongation is 5.2%. © 2010, Northwest Institute for Nonferrous Metal Research. Published by Elsevier BV. All rights reserved.


Zhang D.-F.,Chongqing University | Zhang D.-F.,National Research Center for Magnesium Alloys | Shi G.-L.,Chongqing University | Zhao X.-B.,Chongqing University | Qi F.-G.,Chongqing University
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2011

The roles of Zn content and thermo-mechanical treatment in affecting microstructures and mechanical properties of Mg-xZn-1Mn (mass fraction, x=4, 5, 6, 7, 8, 9) wrought Mg alloys were investigated. The microstructure was extremely refined by dynamic recrystallization (DRC) during extrusion. With increasing Zn content, the DRC grains tended to grow up, at the same time, more second phase streamlines would be present, which restricted the further growing. During solution treatment, the DRC grains would rapidly grow up; however, higher Zn content could hinder the grain boundary expanding, which results in finer ultimate grains. MgZn2 dispersoid particles which are coherent with the matrix would precipitate from the supersaturated solid solution during the one-step aging process, and nano-sized GP zones formed during the pre-aging stage of the two-step aging provide a huge amount of effective nuclei for the MgZn2 phases formed in the second stage, which makes the MgZn 2 particles much finer and more dispersed. The mechanical properties of as-extruded samples were not so sensitive to the variation of Zn content, the tensile strength fluctuates between 300 and 320 MPa, and the elongation maintains a high value between 11 and 14. The strength of aged samples rises as a parabolic curve with increasing Zn content, specifically, the tensile strength of one-step aged samples rises from 278 to 374 MPa, and that of two-step aged ones rises from 284 to 378 MPa, yet the elongation of all aged samples is below 8. When Zn content exceeds its solid solution limit in Mg-Zn system (6.2, mass fraction), the strength rises slowly but the elongation deteriorates sharply, so a Mg-Zn-Mn alloy with 6 Zn possesses the best mechanical properties, that is, the tensile strengths after one- and two-step aging are 352 and 366 MPa, respectively, and the corresponding elongations are 7.98 and 5.2, respectively. © 2011 The Nonferrous Metals Society of China.


Zhang D.-F.,Chongqing University | Zhang D.-F.,National Research Center for Magnesium Alloys | Zhu Z.-T.,Chongqing University | Wu Y.,Chongqing University | And 4 more authors.
Cailiao Rechuli Xuebao/Transactions of Materials and Heat Treatment | Year: 2013

Effects of different heat treatment on microstructure and properties of wrought Mg-Zn-Mn (ZM61) alloy were studied by means of optical microscopy, electronic microscopy and EDS, hardness tests, tensile tests and XRD analysis. The results show that the new ZM61 alloy can be smoothly extruded at 420°C, complete dynamic recrystallization takes place and fine recrystallized grains are formed during this process. Compared with the as-extruded alloy, T5 treatment can improve the strength of the ZM61 alloy, and the properties of the ZM61 magnesium are further improved by solution and aging treatments (T6, T4 + two-stage aging), the tensile strength of the alloy can be up to 362 MPa after T4 + 2-step-aging. It is confirmed that the solution treatment is very necessary before aging, and the best solution treatment process of wrought ZM61 alloy is 420°C × 2 h. The failure mode of the ZM61 alloy directly aged after extrusion(T5) is mixed fracture, but cleavage fracture prevails for the alloy after solution and aging treatment.


Zhang D.,Chongqing University | Zhang D.,National Research Center for Magnesium Alloys | Zhao X.,Chongqing University | Shi G.,Chongqing University | Qi F.,Chongqing University
Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering | Year: 2011

The roles of Zn content and thermomechanical treatment in affecting microstructures and mechanical properties of Mg-x wt%Zn-1wt%Mn (x=4, 5, 6, 7, 8, 9) wrought Mg alloys were investigated. The microstructure during extrusion was extremely refined by dynamic recrystallization (DRC). As Zn content increasing, the DRC grains tended to grow up; at the same time, more second phase streamlines would be present which restricted their further growth. During solution treatment, the DRC grains would rapidly grow up; however, more Zn content could obstruct the grain boundary expanding which resulted in finer grains. The microstructures of the aged specimens were examined by transmission electron microscopy (TEM). The age-hardening resulted mainly from two metastable phases, known as β 1′ and β 2′, the interfaces between which and the matrix were coherent or semicoherent. β 1′ phases formed as rods with their long axis parallel to the [0001] α direction of the α-Mg matrix could act as a more enormous impediment to the motion of dislocations than β 2′ formed as plates on (0001) α. Based on X-ray diffraction, both phases might be the Laves phase MgZn 2. Compared with the one-step aging, β 1′ and β 2′ in two-step aged alloys were much finer and more dispersed, since nano-sized and coherent G.P. zones formed during the pre-aging stage provided more effective nuclei for the two phases during the second stage. Higher Zn content was apt to cause overaging, so large Mg-Zn blocks were formed by consuming β 1′ and β 2′ after aging at 180 °C for 16 h. Mn was present as rod-shaped precipitates in the aged specimens, which could act as nuclei for β 1′ and β 2′ and drive them into coarser ones. The mechanical properties of as-extruded samples were not so sensitive to the changes of Zn content. The strength of as-aged samples rose as a parabolic curve with the increasing of Zn content, while Zn content exceeded its solid solution limit in Mg (6.2 wt%), strength rising became slow, and the elongation quickly deteriorated, so a Mg-Zn-Mn alloy with 6wt% Zn possessed the best mechanical properties.

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