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Mechanical Properties and Fracture Behavior of Mg-Al/AlN Composites with Different Particle Contents
Chen Jie, Bao Chonggao, Chen Wenhui, Zhang Li, Liu Jinling
J. Mater. Sci. Technol.    2017, 33 (7): 668-674.   DOI: 10.1016/j.jmst.2016.07.010
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In this study, magnesium matrix composites reinforced with different loading of AlN particles were fabricated by the powder metallurgy technique. The microstructure, bending strength and fracture behavior of the resulting Mg-Al/AlN composites were investigated. It showed that the 5 wt% AlN reinforcements led to the highest densification and bending strength. The total strengthening effect of AlN particles was predicted by considering the contributions of CTE mismatch between the matrix and the particles, load bearing and Hall-Petch mechanism. The results revealed that the increase of dislocation density, the change of Mg17Al12 phase morphology, and the effective load transfer were the major strengthening contributors to the composites. The fracture of the composites altered from plastic to brittle mode with increasing reinforcement content. The regions of clustered particles in the composites were easy to be damaged under external load, and the fracture occurred mainly along grain boundaries.

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Protective Composite Coatings Formed on Mg Alloy Surface by PEO Using Organofluorine Materials
V. Mashtalyar Dmitry, V. Nadaraia Konstantine, L. Sinebryukhov Sergey, V. Gnedenkov Sergey
J. Mater. Sci. Technol.    2017, 33 (7): 661-667.   DOI: 10.1016/j.jmst.2016.09.006
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The results of the surface modification of magnesium alloys by plasma electrolytic oxidation (PEO) and subsequent treatment in suspension of the superdispersed polytetrafluoroethylene (SPTFE) or telomeric solution of tetrafluoroethylene (TFE) are presented. Composite coatings have been obtained by dipping with subsequent heat treatment. Electrochemical, tribological properties and wettability of protective composite coatings have been investigated. Composite coatings formed on PEO-layer by fourfold treatment of samples in SPTFE suspension possess best protective properties. The obtained coatings decrease the corrosion current density (5.4 × 10-11 A cm-2) and wear (7.6 × 10-7 mm3 (N m)-1), and increase the polarisation resistance (1.7 × 109 Ω cm2) and impedance modulus (1.9 × 109 Ω cm2) by orders of magnitude in comparison with unprotected magnesium alloy and base PEO-coating. The highest value of contact angle (CA) has been obtained for coatings with triple application in telomeric solution. CA for such composite coatings attains (171 ± 2)°, as the result of multimodal roughness of the composite coating's surface.

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Superior Properties of Mg-4Y-3RE-Zr Alloy Prepared by Powder Metallurgy
Kubásek Ji?í, Dvorsky Drahomír, ?avojsky Miroslav, Vojtěch Dalibor, Beronská Nad'a, Fousová Michaela
J. Mater. Sci. Technol.    2017, 33 (7): 652-660.   DOI: 10.1016/j.jmst.2016.09.019
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Magnesium alloys are important materials for application in the automotive and aviation industries. During the last few years, the number of possible applications as biodegradable implants in medicine has grown. Mg-RE (rare earth) alloys belong to the most advanced group of products, offering the best combination of mechanical properties and corrosion resistance. Among these materials, WE43 (Mg-Y-Nd) is a very well-known commercial alloy that has been extensively studied for applications at increased temperatures and also in organisms. Although this material has been described, there are still possibilities to improve its properties and subsequently expand its applicability. Powder metallurgy has already been used for the preparation of magnesium alloys with superior mechanical properties and occasionally superior corrosion properties. Therefore, the present paper is oriented toward the preparation of Mg-4Y-3RE-Zr (WE43) alloy by the powder metallurgy technique (WE43-PM) and comparison of the final properties with the product of extrusion of as-cast ingot (WE43-IM). Our processing leads to a partial improvement in the mechanical properties and superior corrosion resistance of WE43-PM. The texture strength of WE43-PM was low, and therefore, anisotropy of mechanical properties was suppressed.

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Effects of Load on Dry Sliding Wear Behavior of Mg-Gd-Zn-Zr Alloys
Zhang Jie, Zhang Xiaobo, Liu Qinghua, Yang Shujie, Wang Zhangzhong
J. Mater. Sci. Technol.    2017, 33 (7): 645-651.   DOI: 10.1016/j.jmst.2016.11.014
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Dry sliding wear tests on as-cast and T6-treated Mg-3Gd-1Zn-0.4Zr (wt%, GZ31K) and Mg-6Gd-1Zn-0.4Zr (wt%, GZ61K) alloys were performed using a ball-on-disk configuration at room temperature. Friction coefficient and wear rate of the alloys were measured under three different applied loads (50 N, 100 N, and 200 N, respectively). Worn surface morphologies were analyzed using a scanning electron microscope (SEM) coupled with an energy dispersive spectrometer (EDS). It is found that the friction coefficient of the alloys decreases with increasing load, except the as-cast GZ61K. The wear rates of the as-cast Mg-Gd-Zn-Zr alloys increase with the increase of the load. However, the wear rates of the T6-treated Mg-Gd-Zn-Zr alloys first increase because of the participation of a large amount of needle-like precipitates, but then decline due to obvious work hardening. The wear mechanisms of abrasion, plastic deformation, oxidation, adhesion and delamination are detected. Abrasion dominates the wear mechanism under the low load; whereas, adhesion is the main wear mechanism under intermediate load, and plastic deformation has great effect on the wear rate under high applied load.

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Constitutive Relationship and Hot Processing Maps of Mg-Gd-Y-Nb-Zr Alloy
Zhou Zhaohui, Fan Qichao, Xia Zhihui, Hao Aiguo, Yang Wenhua, Ji Wei, Cao Haiqiao
J. Mater. Sci. Technol.    2017, 33 (7): 637-644.   DOI: 10.1016/j.jmst.2015.10.019
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The hot working behavior of Mg-Gd-Y-Nb-Zr alloy was investigated using constitutive model and hot processing maps in this work. Isothermal compression tests were conducted with temperature and strain rate range of 703-773 K and 0.01-5 s-1, respectively. Improved Arrhenius-type equation incorporated with strain compensations was used to predict flow behavior of the alloy, and the predictability was evaluated using correlation coefficient, root mean square error and absolute relative error. Processing maps were constructed at different strains for Mg-Gd-Y-Nb-Zr alloy based on dynamic materials model. The processing maps are divided into three domains and the corresponding microstructure evolutions are referred to the forming of straight grain boundaries, twinning, dynamic recrystallization and grain growth. Instability occurred mainly at the strain rate range of 0.3s-1-0.5s-1. The optimum processing domain is mainly at the temperature range of 703-765 K with the strain rate range of 0.01-0.1 s-1.

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Effect of rolling deformation on microstructure and texture of spray-deposited magnesium alloy containing Mg-Nd-Zn typed LPSO
Li Zhenliang, Liu Fei, Yuan Aiping, Duan Baoyu, Li Yiming, Li Xiaowei
J. Mater. Sci. Technol.    2017, 33 (7): 630-636.   DOI: 10.1016/j.jmst.2017.02.003
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Billets of Mg-9Al-3Zn-1Mn-6Ca-2Nd alloy were produced by spray-deposition (the Osprey process). Effect of rolling deformation (T = 350 °C, ε = 5%, 10%, and 15%, respectively) on microstructure and texture evolution of the Mg-9Al-3Zn-1Mn-6Ca-2Nd alloy was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Results show that at pass reduction of ε = 5%, 10% and 15% at 350 °C respectively, Mg-Nd-Zn typed 24R-LPSO structure was formed in (Ca, Nd)Al2 phase (C15 Laves phase). With the increase in pass reduction (i.e. 5%, 10% and 15%), the texture pole density level of basal texture (0002) changed little and pyramidal texture (101?3) were increased. In contrast, those of prismatic texture {101?0} <112?0> were increased initially and followed by a reduction, indicating texture randomization in the grain-refined Mg alloy. The combined contribution of LPSO phase and C15 phase was key to randomize the texture of the grain-refined Mg alloy. It was noted that the microcosmic plastic deformation of LPSO phase and nanometer-sized dispersed C15 phase impeded dislocation movement, led to dislocation tangles, and facilitated recrystallization.

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Enhanced Damping Capacities of Mg-Ce Alloy by the Special Microstructure with Parallel Second Phase
Wu Zhongshan, Wang Jingfeng, Wang Haibo, Ma She, Huang Song, Li Shun, Pan Fusheng
J. Mater. Sci. Technol.    2017, 33 (9): 941-946.   DOI: 10.1016/j.jmst.2016.06.027
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Microstructure evolution and damping capacities of Mg-Ce binary alloys with three different Ce contents (0.5, 1, or 2 wt%) have been systematically investigated in this work. Numerous fine parallel second phases in Mg-2Ce alloy are obtained, as well as a large number of dislocations around them, but few dislocations appear around the reticular second phase in the Mg-1Ce alloy. Among the three alloys, two internal friction peaks (P1 and P2) are detected at about 78 and 167°C in both the Mg-0.5Ce and Mg-1Ce alloys. In addition, the alloy with special parallel second phase structure exhibits excellent damping capacity in both strain amplitude and temperature-dependent regions. These results may be ascribed to the stress concentration and the formation of abundant parallel and uniform dislocation configurations in the α-Mg matrix without the influence of crystal orientation. The obtained results may provide a novel idea to prepare high-damping magnesium alloys by tailoring their microstructure.

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Pitting corrosion of a Rare Earth Mg alloy GW93
Song Yingwei, Shan Dayong, Han En-Hou
J. Mater. Sci. Technol.    2017, 33 (9): 954-960.   DOI: 10.1016/j.jmst.2017.01.014
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Pitting corrosion of magnesium (Mg) alloys is greatly associated with their microstructure, especially second phases. The second phases in traditional Mg alloys such as AZ91 are electrochemically nobler than Mg matrix, while the second phases in Rare earth (RE) Mg alloy GW93 are more active than Mg matrix. As a result, the pitting corrosion mechanism of Mg alloy GW93 is different from the traditional ones. This paper aims to clarify the pitting corrosion mechanism of Mg alloy GW93 through the studies of Volta potential by Scanning Kelvin Probe Force Microscopy (SKPFM), corrosion morphology by Scanning Electron Microscope (SEM), and corrosion resistance by electrochemical tests. Results reveal that the pitting corrosion of GW93 includes three stages, first, dissolution of the second phases, followed by corrosion of Mg matrix adjacent to the dissolved second phases, and finally, propagation of corrosion pits along the depth direction of the dissolved second phases. Anodic second phases and enrichment of Cl- in the thick corrosion product films dominate the propagation of pitting corrosion.

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Microstructure and mechanical properties at elevated temperature of Mg-Al-Ni alloys prepared through powder metallurgy
Hou Legan, Li Bingcheng, Wu Ruizhi, Cui Lin, Ji Peng, Long Ruiying, Zhang Jinghua, Li Xinlin, Dong Anping, Sun Baode
J. Mater. Sci. Technol.    2017, 33 (9): 947-953.   DOI: 10.1016/j.jmst.2017.02.002
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Mg-Al-Ni alloys were prepared by powder metallurgy, and their microstructure and elevated temperature mechanical properties were investigated. Results indicate that, in addition to α-Mg matrix, both coarse Al3Ni2 particles and fine AlNinano-particles exist in the Mg-Al-Ni alloys. The strength at 150℃ is improved with the increase in Ni content. Mg-18.3Al-8Ni alloy possesses a compressive strength of 234.7 MPa and a yield strength of 146.5 MPa. Plasticity is also improved with a low concentration of Ni. Mg-11.3Al-2Ni alloy possesses a compression ratio of 17.3%. The phases of Al3Ni2 and AlNi in the alloys block the movements of grain boundaries and dislocations during the deformation at elevated temperature. The existence of AlNi phase provides a non-basal slip system, leading to the improvement in plasticity. Finally, the formation mechanism of Al-Ni phases in the process is discussed with thermodynamics and kinetics.

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Effect of Nd on microstructure and mechanical properties of as-extruded Mg-Y-Zr-Nd alloy
Xu Xiaoyang, Chen Xianhua, Du Weiwei, Geng Yuxiao, Pan Fusheng
J. Mater. Sci. Technol.    2017, 33 (9): 926-934.   DOI: 10.1016/j.jmst.2017.04.011
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The microstructure and mechanical properties of Mg-Y-Zr-xNd alloys with 0-2.63 wt% Nd were investigated using optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction and tensile testing test. Results indicated that more Mg24Y5 particles and Mg14Nd2Y (β) phases were dispersed in the matrix when Nd content increased from 0 wt% to 2.63 wt% in the extruded alloys. Consequently, the nucleation of dynamic recrystallization and the volume fraction of recrystallized grains were promoted obviously. The average grain size can be refined in the range of 4.6-1.3 μm after the addition of 2.63 wt% Nd. The tensile strength of extruded alloys increased with increasing Nd content, and elongation exhibited an opposite change tendency. The extruded alloy sheet with 1.01 wt% Nd demonstrates optimal combination of strength and plasticity, i.e., the ultimate tensile strength, yield strength, and elongation were 273 MPa, 214 MPa, and 24.2%, respectively. Variations in mechanical properties are discussed on the basis of microstructure observations.

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