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Terence G Langdon - One of the best experts on this subject based on the ideXlab platform.
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analysis of the creep behavior of fine grained Az31 magnesium Alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2020Co-Authors: Roberto B Figueiredo, Terence G LangdonAbstract:Abstract Double-shear creep testing was used to evaluate the creep behavior of a magnesium Az31 Alloy processed by equal-channel angular pressing to produce an average grain size of ~2.7 μm. The results show that rapid creep rates are observed in the early stages of deformation due to the occurrence of grain boundary sliding in the fine-grained structure but the creep rates decrease with increasing deformation due to grain growth. The stress exponent for flow in the early stages is ~2 and the activation energy is ~92 kJ mol−1 where these values are consistent with the expectations for grain boundary sliding under superplastic conditions. Annealing the material for 24 h at 723 K before creep testing produces a significantly larger grain size of ~50 μm and this prevents grain boundary sliding and leads to an increasing stress exponent at higher stresses. Deformation mechanism maps are constructed incorporating both the present experimental results for a fine-grained magnesium Alloy and results from published data for the Az31 Alloy. These maps provide a useful tool for evaluating the experimental conditions that are necessary for achieving superplastic forming operations.
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hardness homogeneity and micro tensile behavior in a magnesium Az31 Alloy processed by equal channel angular pressing
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013Co-Authors: Debin Shan, Mahmood Shirooyeh, Jittraporn Wongsangam, Jie Xu, Terence G LangdonAbstract:Abstract A magnesium Az31 Alloy was processed by equal-channel angular pressing (ECAP) at a temperature of 473 K using a die with a channel angle of 110°. The results show that an ultrafine-grained (UFG) microstructure is achieved with good hardness homogeneity after processing through 4 or more passes of ECAP. After 8 passes of ECAP, a grain size of ~1.0 μm was achieved. Measurements show that the average value of the microhardness increases with increasing numbers of ECAP passes. The mechanical properties were evaluated using micro-tensile testing with specimens cut perpendicular to the longitudinal axes of the ECAP billets. These tests were conducted at room temperature and at 423 and 473 K and the results demonstrate a potential for using the UFG Az31 Alloy for applications in micro-forming technology.
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Significance of twinning in the anisotropic behavior of a magnesium Alloy processed by equal-channel angular pressing
Scripta Materialia, 2010Co-Authors: Roberto B Figueiredo, Zuzanka Trojanová, Pavel Lukáč, Zoltan Szaraz, Terence G LangdonAbstract:An extruded magnesium Az31 Alloy was processed by equal-channel angular pressing (ECAP) and then tested in compression using three orthogonal orientations. The results reveal a significant anisotropy in the mechanical behavior, which is affected by the ECAP processing. The tendency for twinning in the extruded Alloy decreases with additional straining when testing along the billet axis, but this tendency increases in the through-thickness direction.
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developing superplasticity in a magnesium Az31 Alloy by ecap
Journal of Materials Science, 2008Co-Authors: Roberto B Figueiredo, Terence G LangdonAbstract:The processing of a magnesium Az31 Alloy by equal-channel angular pressing refines the grain size to ~2.2 μm, but annealing for 30 min at 673 K coarsens the grains to ~6.0 μm. Despite this microstructural instability, the Alloy is superplastic when pulled in tension at temperatures in the range of 623–723 K with elongations up to >1000% at strain rates at and below 10−4 s−1. Experiments within the superplastic regime show the strain rate sensitivity is ~0.5 and the activation energy is close to the value for grain boundary diffusion. It is demonstrated by calculation that the experimental results are in good agreement with a model for superplasticity based on grain boundary sliding.
Nack J Kim - One of the best experts on this subject based on the ideXlab platform.
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Effect of Sn addition on the microstructure and deformation behavior of Mg-3Al Alloy
Acta Materialia, 2017Co-Authors: Byeong-chan Suh, Jae H. Kim, Jun Ho Bae, Ji Hyun Hwang, Myeong-shik Shim, Nack J KimAbstract:Mg Alloys generally suffer from their poor formability at low temperatures due to their strong basal texture and a lack of adequate deformation systems. In the present study, a small amount of Sn was added instead of Zn to Mg-3Al Alloy to modify its deformation behavior and improve the stretch formability. Microstructural examinations of the deformed Mg-3Al-1Sn (AT31) Alloy by electron backscatter diffraction and transmission electron microscopy show that prismatic slip is quite active during deformation, resulting in much lower r-values and planar anisotropy than the counterpart Mg-3Al-1Zn (Az31) Alloy. Polycrystal plasticity simulation based on visco-plasticity self-consistent (VPSC) model also shows that prismatic slip is the dominant deformation mode in AT31 Alloy besides basal slip. As a consequence, AT31 Alloy shows a much higher stretch formability than Az31 Alloy. On the other hand, Az31 Alloy shows the development of intense shear bands during stretch forming, and these shear bands act as crack propagating paths, limiting the stretch formability of Az31 Alloy.
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superplastic deformation behavior of twin roll cast mg 6zn 1mn 1al Alloy
Scripta Materialia, 2009Co-Authors: Sung Soo Park, Geun Tae Bae, D H Kang, Bongsun You, Nack J KimAbstract:The high-temperature deformation behavior of twin-roll cast (TRC) Mg–6Zn–1Mn–1Al (ZMA611) Alloy has been investigated and compared with that of ingot cast (IC) Mg–3Al–1Zn (Az31) Alloy. At 543–603 K and at 10−4–10−2 s−1, TRC ZMA611 Alloy shows much larger tensile elongation at a faster strain rate than IC Az31 Alloy. The superplastic properties of TRC ZMA611 Alloy are mainly due to the presence of thermally stable fine particles, which stabilize grain size and hence promote grain boundary sliding.
Rongchang Zeng - One of the best experts on this subject based on the ideXlab platform.
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corrosion resistance of a novel sno2 doped dicalcium phosphate coating on Az31 magnesium Alloy
Bioactive Materials, 2017Co-Authors: Lanyue Cui, Rongchang Zeng, Guangbin Wei, Yuhong Zou, Enhou HanAbstract:Abstract A SnO2-doped dicalcium phosphate coating was prepared on Az31 Alloy by means of hydrothermal deposition. The results showed that the coating possessed a globular morphology with a long lamellar crystalline structure and a thickness of approximately 40 μm. The surface of the coating became smooth with an increase additive amount of the SnO2 nanoparticles. The corrosion current density and hydrogen evolution rate of the coating prepared in presence of SnO2 were reduced compared to the coating without SnO2 and the bare Az31 substrate, indicating an improvement in the corrosion resistance of the SnO2-doped coating.
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new insights into the effect of tris hcl and tris on corrosion of magnesium Alloy in presence of bicarbonate sulfate hydrogen phosphate and dihydrogen phosphate ions
Journal of Materials Science & Technology, 2017Co-Authors: Yan Hu, Rongchang Zeng, Yongxin Yang, Shuoqi Li, Fen ZhangAbstract:In vitro degradation is an important approach to screening appropriate biomedical magnesium (Mg) Alloys at low cost. However, corrosion products deposited on Mg Alloys exert a critical impact on corrosion resistance. There are no acceptable criteria on the evaluation on degradation rate of Mg Alloys. Understanding the degradation behavior of Mg Alloys in presence of Tris buffer is necessary. An investigation was made to compare the influence of Tris-HCl and Tris on the corrosion behavior of Mg Alloy Az31 in the presence of various anions of simulated body fluids via hydrogen evolution, pH value and electrochemical tests. The results demonstrated that the Tris-HCl buffer resulted in general corrosion due to the inhibition of the formation of corrosion products and thus increased the corrosion rate of the Az31 Alloy. Whereas Tris gave rise to pitting corrosion or general corrosion due to the fact that the hydrolysis of the amino-group of Tris led to an increase in solution pH value, and promoted the formation of corrosion products and thus a significant reduction in corrosion rate. In addition, the corrosion mechanisms in the presence of Tris-HCl and Tris were proposed. Tris-HCl as a buffer prevented the formation of precipitates of HCO3−, SO42−, HPO42− and H2PO4− ions during the corrosion of the Az31 Alloy due to its lower buffering pH value (x.x). Thus, both the hydrogen evolution rate and corrosion current density of the Alloy were approximately one order of magnitude higher in presence of Tris-HCl than Tris and Tris-free saline solutions.
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corrosion resistance of a self healing micro arc oxidation polymethyltrimethoxysilane composite coating on magnesium Alloy Az31
Corrosion Science, 2017Co-Authors: Pingping Li, Rongchang Zeng, Fen Zhang, Shuoqi LiAbstract:Abstract A micro-arc oxidation (MAO)/polymethyltrimethoxysilane (PMTMS) hybrid coating was fabricated via MAO processing and subsequent sealing with alkaline treatment and PMTMS. The surface morphologies, chemical compositions and corrosion resistances of the coatings were investigated using FE-SEM, FTIR, XRD and electrochemical and hydrogen evolution measurements. The results indicated that the alkaline treatment was beneficial to the silane treatment and that the MAO coating was efficiently sealed by the PMTMS film. The MAO/PMTMS coating significantly enhanced the corrosion resistance of the Az31 Alloy due to its self-healing function. Additionally, we suggest and discuss a corrosion mechanism for the coating.
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corrosion resistance of biodegradable polymeric layer by layer coatings on magnesium Alloy Az31
Frontiers of Materials Science, 2016Co-Authors: Lanyue Cui, Rongchang Zeng, Xiaoxiao Zhu, Tingting Pang, Fen ZhangAbstract:Biocompatible polyelectrolyte multilayers (PEMs) and polysiloxane hybrid coatings were prepared to improve the corrosion resistance of biodegradable Mg Alloy Az31. The PEMs, which contained alternating poly(sodium 4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH), were first self-assembled on the surface of the Az31 Alloy substrate via electrostatic interactions, designated as (PAH/PSS)5/Az31. Then, the (PAH/PSS)5/Az31 samples were dipped into a methyltrimethoxysilane (MTMS) solution to fabricate the PMTMS films, designated as PMTMS/(PAH/PSS)5/Az31. The surface morphologies, microstructures and chemical compositions of the films were investigated by FE-SEM, FTIR, XRD and XPS. Potentiodynamic polarization, electrochemical impedance spectroscopy and hydrogen evolution measurements demonstrated that the PMTMS/(PAH/PSS)5/Az31 composite film significantly enhanced the corrosion resistance of the Az31 Alloy in Hank’s balanced salt solution (HBSS). The PAH and PSS films effectively improved the deposition of Ca-P compounds including Ca3(PO4)2 and hydroxyapatite (HA). Moreover, the corrosion mechanism of the composite coating was discussed. These coatings could be an alternative candidate coating for biodegradable Mg Alloys.
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in vitro corrosion and antibacterial performance of polysiloxane and poly acrylic acid gentamicin sulfate composite coatings on Az31 Alloy
Surface & Coatings Technology, 2016Co-Authors: Lijun Liu, Fen Zhang, Yuhong Zou, Kaijie Luo, Rongchang ZengAbstract:Abstract An investigation on the corrosion resistance and antibacterial properties of polyelectrolytes and polysiloxane coatings on magnesium Alloy with gentamicin was made. The microstructure and composition of the multilayer coatings were characterized by using Fourier transform infrared spectroscopy, X-ray diffractometer and scanning electron microscopy. The analysis of electrochemical measurement in HBSS suggested that the composite coatings improved the corrosion resistance of Az31 Alloy. Finally, the result of plate-counting method demonstrates the effective antibacterial properties of the functionalized substrates. Thus, it can be concluded that the multilayer-treatment reported here is a versatile approach to develop antibacterial and anticorrosion coatings on magnesium implants.
Roberto B Figueiredo - One of the best experts on this subject based on the ideXlab platform.
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analysis of the creep behavior of fine grained Az31 magnesium Alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2020Co-Authors: Roberto B Figueiredo, Terence G LangdonAbstract:Abstract Double-shear creep testing was used to evaluate the creep behavior of a magnesium Az31 Alloy processed by equal-channel angular pressing to produce an average grain size of ~2.7 μm. The results show that rapid creep rates are observed in the early stages of deformation due to the occurrence of grain boundary sliding in the fine-grained structure but the creep rates decrease with increasing deformation due to grain growth. The stress exponent for flow in the early stages is ~2 and the activation energy is ~92 kJ mol−1 where these values are consistent with the expectations for grain boundary sliding under superplastic conditions. Annealing the material for 24 h at 723 K before creep testing produces a significantly larger grain size of ~50 μm and this prevents grain boundary sliding and leads to an increasing stress exponent at higher stresses. Deformation mechanism maps are constructed incorporating both the present experimental results for a fine-grained magnesium Alloy and results from published data for the Az31 Alloy. These maps provide a useful tool for evaluating the experimental conditions that are necessary for achieving superplastic forming operations.
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Significance of twinning in the anisotropic behavior of a magnesium Alloy processed by equal-channel angular pressing
Scripta Materialia, 2010Co-Authors: Roberto B Figueiredo, Zuzanka Trojanová, Pavel Lukáč, Zoltan Szaraz, Terence G LangdonAbstract:An extruded magnesium Az31 Alloy was processed by equal-channel angular pressing (ECAP) and then tested in compression using three orthogonal orientations. The results reveal a significant anisotropy in the mechanical behavior, which is affected by the ECAP processing. The tendency for twinning in the extruded Alloy decreases with additional straining when testing along the billet axis, but this tendency increases in the through-thickness direction.
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developing superplasticity in a magnesium Az31 Alloy by ecap
Journal of Materials Science, 2008Co-Authors: Roberto B Figueiredo, Terence G LangdonAbstract:The processing of a magnesium Az31 Alloy by equal-channel angular pressing refines the grain size to ~2.2 μm, but annealing for 30 min at 673 K coarsens the grains to ~6.0 μm. Despite this microstructural instability, the Alloy is superplastic when pulled in tension at temperatures in the range of 623–723 K with elongations up to >1000% at strain rates at and below 10−4 s−1. Experiments within the superplastic regime show the strain rate sensitivity is ~0.5 and the activation energy is close to the value for grain boundary diffusion. It is demonstrated by calculation that the experimental results are in good agreement with a model for superplasticity based on grain boundary sliding.
D H Kang - One of the best experts on this subject based on the ideXlab platform.
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Development of strip casting process for fabrication of wrought Mg Alloys
'Trans Tech Publications Ltd.', 2019Co-Authors: Ss Park, D H Kang, Gt BaeAbstract:Az31 and experimental ZMA61 I Alloys were strip cast into 2 mm. thick strips. The as-cast Az31 Alloy strip consists of columnar dendrites. On the other hand, as-cast ZMA61 I Alloy strip shows equiaxed dendritic structure through the thickness of strip. Strip cast Az31 Alloy in H24 condition has equivalent yield and tensile strengths with similar ductility compared to commercial ingot cast Az31-H24 Alloy, indicating that strip casting is a viable process for the fabrication of Mg Alloy strips. The ZMA611 Alloy has a large volume fraction of fine dispersoid particles in the microstructure, resulting from the beneficial effect of strip casting on microstructural refinement. It has been shown that the ZMA611 Alloy has superior tensile properties compared to commercial ingot cast AD31-H24 Alloy, suggesting the possibility of the development of new wrought Mg Alloy sheets by strip casting.X1124sciescopu
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Development of Mg Alloy sheets via strip casting
'Trans Tech Publications Ltd.', 2019Co-Authors: Ss Park, Ym Kim, D H KangAbstract:Az31 and experimental ZMA611 Alloys were strip cast into 2 min thick strips. The as-cast Az31 Alloy strip consists of columnar dendrites. On the other hand, as-cast ZMA611 Alloy strip shows equiaxed dendritic structure through the thickness of strip. These Alloys were subjected to various thermomechanical treatments and their tensile properties were evaluated. Strip cast Az31 Alloy in H24 condition has equivalent yield and tensile strengths with similar ductility compared to commercial ingot cast Az31-H24 Alloy, indicating that strip casting is a viable process for the fabrication of Mg Alloy strips. The ZMA611 Alloy has a large volume fraction of fine dispersoid particles in the microstructure, resulting from the beneficial effect of strip casting on microstructural refinement. It has been shown that the ZMA611 Alloy has superior tensile properties compared to commercial ingot cast Az31-H24 Alloy, suggesting the possibility of the development of new wrought Mg Alloy sheets by strip casting.X1125sciescopu
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MICROSTRUCTURE AND MECHANICAL PROPERTIES OF TWIN-ROLL STRIP CAST MG AlloyS
'Trans Tech Publications Ltd.', 2019Co-Authors: Ss Park, D H Kang, Gt Bae, Ks ShinAbstract:Development of wrought Mg Alloys, particularly in sheet form, is essential to support the growing interest for lightweight components in the automotive industry. However, development of Mg Alloy sheets has been quite slow due to the complexity of sheet production originated from limited deformability of Mg. In this respect, twin-roll strip casting, a one-step processing of flat rolled products, can be an alternative for the production of Mg Alloy sheets. In this study, Az31 and experimental ZM series Alloys are twin-roll strip cast into 2 mm thick sheets. The microstructure of the as-cast Az31 Alloy sheet consists of columnar zones near the roll side and equiaxed zones in the mid-thickness region. On the other hand, as-cast ZM series Alloy sheets show equiaxed dendritic structure through the thickness of sheet. These Alloys were subjected to various thermo-mechanical treatments and their tensile properties were evaluated. Twin-roll strip cast Az31 Alloy in H24 condition has equivalent yield and tensile strengths with similar ductility compared to commercial ingot cast Az31-H24 Alloy, indicating that twin-roll strip casting is a viable process for the fabrication of Mg Alloy sheets. The experimental ZM series Alloys have a large volume fraction of fine dispersoid particles in the microstructure, resulting from the beneficial effect of twin-roll strip casting on microstructural refinement. It has been shown that the experimental ZM series Alloys have superior tensile properties compared to commercial ingot cast Az31-H24 Alloy, suggesting the possibility of the development of new wrought Mg Alloy sheets by twin-roll strip casting.1110Nsciescopu
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Superplastic deformation behavior of twin-roll cast Mg-6Zn-1Mn-1Al Alloy
'Elsevier BV', 2019Co-Authors: Ss Park, D H Kang, Gt Bae, Bs You, Nj KimAbstract:The high-temperature deformation behavior of twin-roll cast (TRC) Mg-6Zn-1Mn-1Al (ZMA611) allot has been investigated and compared with that of ingot cast (IC) Mg-3Al-1Zn (Az31) Alloy. At 543-603 K and at 10(-4)-10(-2) s(-1), TRC ZMA611 Alloy shows much larger tensile elongation at a faster strain rate than IC Az31 Alloy. The superplastic properties of TRC ZMA611 Alloy are mainly due to the presence of thermally stable fine particles, which stabilize grain size and hence promote grain boundary sliding. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.X1132sciescopu
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superplastic deformation behavior of twin roll cast mg 6zn 1mn 1al Alloy
Scripta Materialia, 2009Co-Authors: Sung Soo Park, Geun Tae Bae, D H Kang, Bongsun You, Nack J KimAbstract:The high-temperature deformation behavior of twin-roll cast (TRC) Mg–6Zn–1Mn–1Al (ZMA611) Alloy has been investigated and compared with that of ingot cast (IC) Mg–3Al–1Zn (Az31) Alloy. At 543–603 K and at 10−4–10−2 s−1, TRC ZMA611 Alloy shows much larger tensile elongation at a faster strain rate than IC Az31 Alloy. The superplastic properties of TRC ZMA611 Alloy are mainly due to the presence of thermally stable fine particles, which stabilize grain size and hence promote grain boundary sliding.