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Microstructures and tensile properties of submerged friction stir processed AZ91 magnesium alloy

Journal of Magnesium and Alloys 2015年第3期3卷 203-209页

作者： Fang Chai Datong Zhang Yuanyuan Li National Engineering Research Center of Near-Net-Shape Forming for Metallic Materials School of Mechanical and Automotive EngineeringSouth China University of TechnologyGuangzhou 510640China

6 mm thick AZ91 casting alloy plates were subjected to normal friction stir processing(NFSP,in air)and submerged friction stir processing(SFSP,under water),and microstructures and tensile properties of the experimental materials were *** FSP,the coarse microstructures in the as-cast condition are replaced by fine and equiaxed grains and the network-like eutecticβ-Mg_(17)Al_(12)phases disappear and are changed into particles pinned at the grain *** results in further grain refinement in comparison with NFSP,and the average grain sizes of the NFSP and SFSP alloys are 8.4±1.3 and 2.8±0.8µm,*** results reveal that the intensity ofβ-Mg_(17)Al_(12)diffraction peaks in the SFSP specimen decreases compared with *** to significant grain refinement,the tensile strength and elongation of the SFSP AZ91 alloy are increased from 262 MPa and 18.9%for the NFSP material to 282 MPa and 25.4%,and the tensile strength(282 MPa)is nearly three times that of the BM(105 MPa).SFSP is an effective approach to refine the grain size and enhance the tensile properties of AZ91 casting alloy.

关键词： Submerged friction stir processing AZ91 magnesium alloy Microstructure Tensile properties

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Cyclic deformation behavior of a high-strength low-alloy(HSLA)magnesium alloy with heterostructures

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Journal of Magnesium and Alloys 2024年第11期12卷 4610-4621页

作者： H.Wang D.T.Zhang C.Qiu D.L.Chen Guangdong Key Laboratory for Advanced Metallic Materials Processing and Forming National Engineering Research Center of Near-net-shape Forming for Metallic MaterialsSouth China University of TechnologyGuangzhou510640China Department of Mechanical Industrial and Mechatronics EngineeringToronto Metropolitan University(Formerly Ryerson University)TorontoOntario M5B 2K3Canada

Strain-controlled cyclic deformation behavior of a high-strength low-alloy(HSLA)Mg-1.2Zn-0.1Ca alloy fabricated via low-temperature extrusion at 150℃ was investigated at different strain *** to the partial dynamic recrystallization(DRX)during extrusion,the extruded HSLA magnesium alloy consisted of a unique heterostructure containing coarse unDRX grains and ultra-fine DRX grains of0.8μm,leading to a high tensile yield strength of 374 MPa and an elongation of 14%.The HSLA magnesium alloy exhibited cyclic stabilization at strain amplitudes of≤0.4%,while cyclic hardening occurred at strain amplitudes of≥0.6%.In contrast,the homogenized alloy with a uniform coarse-grained microstructure showed a strong cyclic hardening *** with the homogenized alloy,the HSLA magnesium alloy had a significantly higher cyclic stress level at all strain amplitudes,along with a longer fatigue life at lower and intermediate strain amplitudes owing to its higher monotonic ***,the homogenized alloy showed a longer fatigue life at a high strain amplitude of 0.8%due to its better ductility and stronger capacity of storing ***{10-12}<10-11>extension twinning occurred in both the homogenized and HSLA samples at high strain amplitudes,twins were primarily formed in the coarse un DRX grains in the compressive phase during cyclic deformation due to the c-axes of un DRX grains perpendicular to the loading direction,with twinning in the ultra-fine DRX grains being *** low-cycle fatigue life of both the homogenized and HSLA samples can be well predicted through an accumulative damage model based on the strain-energy density calculation and intrinsic fatigue toughness concept.

关键词： High-strength low-alloy(HSLA)magnesium alloy Low-temperature extrusion Heterostructure Low-cycle fatigue Cyclic deformation

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Fracture toughness of multiphase TiAl-Nb alloy in situ consolidated by spark plasma sintering

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Journal of Central South University 2011年第6期18卷 1802-1807页

作者：杨鑫奚正平刘咏汤慧萍胡可贾文鹏 State Key Laboratory of Powder Metallurgy Central South University State Key Laboratory of Porous Metal Materials Northwest Institute for Nonferrous Metal Research National Engineering Research Center of Near-Net-Shape Forming for Metallic Materials South China University of Technology

A fine-grained TiAl alloy with a composition of Ti-45Al-5Nb-1.5Cr-0.2W （mole fraction, %） with multiphases was prepared by spark plasma sintering （SPS） and heat-treating at 1 100 ℃ for 48 h. The relationship among sintering temperature, microstructure and fracture toughness were investigated by X-ray diffractometry （XRD）, optical microscopy （OM）, scanning electron microscopy （SEM） and mechanical testing. The results show that microstructure of the bulk alloy depends on the sintering temperature strongly, and the main phase TiAl and few phases Ti3Al and niobium solid solution （Nbss） are observed in the SPS bulk samples. In the heat-treatment condition, the lamellar and Nbss phase can provide significant toughening by plastic strengthening, interface decohension, crack branch and crack bridge mechanisms. The fracture mode of the SPS TiAl composite samples is intergranular rupture and cleavage fracture.

关键词： TiAl-Nb alloy spark plasma sintering fracture toughness microstructure

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Microstructure and superplasticity of AZ91 magnesium alloy prepared by friction stir processing underwater

Microstructure and superplasticity of AZ91 magnesium alloy p...

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materials Science and Technology Conference and Exhibition 2014, MS and T 2014

作者： Datong, Zhang Fang, Chai National Engineering Research Center of Near-net-shape Forming for Metallic Materials South China University of Technology Guangzhou510640 China

ISBN: (纸本)9781634397230

Submerged friction stir processing (SFSP), which means the entire process is carried out under water, is an improved technique to normal FSP for refining the microstructure of metallic materials. In this study, microstructure and tensile behaviors of AZ91 magnesium alloy prepared by SFSP are investigated. Thermal history during SFSP is also measured, and its effect on the microstructure evolution during SFSP is discussed. SFSP results in significant grain refinement due to the enhanced cooling rate, and a fine-grained AZ91 alloy with an average size of 1.2 micrometers is produced. The SFSP specimens exhibit excellent high strain rate superplasticity, with an elongation of 990% at a strain rate of 0.02 per second and 623K. Grain boundary sliding is the main mechanism during superplastic deformation. The excellent superplasticity of the SFSP alloy is attributed to its fine grain structures, which contain a large fraction of high-angle grain boundary. Copyright © 2014 MS&T14®.

关键词： Magnesium alloys

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Exploring the Formation Mechanism of Deformation Twins in CrMnFeCoNi High Entropy Alloy

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Acta Metallurgica Sinica(English Letters) 2022年第8期35卷 1275-1280页

作者： Junwei Xie Haokai Dong Yuxiu Hao Zhongding Fan Chang-An Wang State Key Lab of New Ceramics and Fine Processing School of Materials Science and EngineeringTsinghua UniversityBeijing 100084China National Engineering Research Center of Near-net-Shape Forming for Metallic Materials South China University of TechnologyGuangzhou 510641China

The deformation twins initiated in CrMnFeCoNi high entropy alloy at cryogenic temperature are experimentally studied. Under the external loading, a three-dimensional shear stress concentration originating from dislocation tangling at both the grain boundaries and twin boundaries could be formed, which promotes emission of partial dislocations from the planar defects and is thus considered to be the key factor for twin formation. A sympathetic nucleation mechanism is proposed to describe the nucleation behaviors of twins.

关键词： High entropy alloy Deformation twinning Defects Shear stress concentration

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Microstructure and brazing mechanism of TiAl/Ni-based superalloy joints using Ti-Zr-Cu-Ni-Co-Mo-B filler metal with different cooling rates 6

Microstructure and brazing mechanism of TiAl/Ni-based supera...

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2020 6th International Conference on materials, Mechanical engineering and Automation Technology, MMEAT 2020

作者： Wan, Bao Li, Xiaoqiang National Engineering Research Center of Near-net-shape Forming for Metallic Materials South China University of Technology Guangzhou510640 China

For the purpose of elevated temperature service and weight reduction in aerospace vehicle applications, a novel Ti-Zr-Cu-Ni-Co-Mo-B filler metal was employed to join TiAl to Ni-based superalloy (GH536). The effect of cooling rate on interfacial microstructure of the joints were analysed by scanning electron microscope and energy dispersive X-ray spectrometer. The representative joint microstructure was primarily composed of six characteristic layers, including TiAl substrate / B2 / τ3 (Al3NiTi2) / τ4 (AlNi2Ti) / Cr-rich (Cr, Ni, Fe)ss, τ4 (AlNi2Ti), Ni-rich (Cr, Ni, Fe)ss and TiNi3) / GH536 substrate. With the decrease of cooling rate in the range of furnace cooling-5 C/min, the joint shear strength firstly increased and then decreased. The joint brazed at 1170 C for 10 min and cooling to 870 C with 10 C/min obtained the maximum shear strength of 252 MPa and the shear fracture mainly occurred in τ3 phase area. © Published under licence by IOP Publishing Ltd.

关键词： Scanning electron microscopy

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Effect of solution treatment on microstructure and mechanical properties of hot-extruded Cu-15Ni-8Sn alloy 17th

Effect of solution treatment on microstructure and mechanica...

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17th IUMRS International Conference in Asia, IUMRS-ICA 2016

作者： Wang, Xun Zhao, Chao Yu, Yan Gen Luo, Zong Qiang Zhang, Wei Wen National Engineering Research Center of Near-net-shape Forming for Metallic Materials South China University of Technology Guangzhou510640 China

ISBN: (纸本)9783035711516

The effects of solution treatment on the microstructure evolution of hot-extruded Cu-15Ni-8Sn alloy were investigated by optical microscope (OM), scanning electronic microscope(SEM), differential scanning calorimetry (DSC) and tensile testing, and the effects of solution temperature and time on the mechanical properties of the alloys were analyzed. The results indicated that, the γ-phases precipitated at first and then dissolved with the extension of the solution time during solutionizing at 800°C,the volume fraction of the γ-phase reached its peak at about 1h. However when solutionizing at 860°C, the γ-phase solely dissolved gradually with the extension of the solution time. In addition, a small amount of annealing twins appeared intragranular in the process of solution treatment. The γ-phase dissolution and the grain growth of α(Cu) were the main softening factors of the alloy during the solution treatment. Through overall consideration, the optimum solution treatment was annealing at 840°C for 1 h. © 2017 Trans Tech Publications, Switzerland.

关键词： Microstructure

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Damage of HVDC AlSiMgMn Alloys Using In-Situ Tensile with X-ray Tomography 75

Damage of HVDC AlSiMgMn Alloys Using In-Situ Tensile with X-...

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75th World Foundry Congress, WFC 2024

作者： Wang, Xueling Zhao, Haidong National Engineering Research Center of Near-Net Shape Forming for Metallic Materials South China University of Technology Guangzhou510641 China

AlSiMgMn alloys with different primary phases were prepared by high vacuum die-casting (HVDC) process. To evaluate the role of Fe-rich intermetallic characteristics on crack initiation, three-dimensional visualization of tensile damage process in these alloys was investigated by in-situ X-ray computed tomography (XCT). The results show that cracks in the alloy with primary α-Al were initiated at connection of shrinkage pore and damaged eutectic intermetallics while clustered primary intermetallics in the alloy with primary α-Fe led to crack formation. © 2024 75th World Foundry Congress, WFC 2024. All rights reserved.

关键词： Vacuum die casting

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Fine-grained Mg-Y-Nd alloy with high-strain-rate superplasticity produced by submerged friction stir processing

Fine-grained Mg-Y-Nd alloy with high-strain-rate superplasti...

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materials Science and Technology Conference and Exhibition 2015, MS and T 2015

作者： Datong, Zhang Gengh, Cao National Engineering Research Center of Near-net-shape Forming for Metallic Materials South China University of Technology Guangzhou510640 China

ISBN: (纸本)9781510813939

Grain refinement is an important method to improve the ductility and formability of magnesium alloys. Submerged friction stir processing (SFSP), which is carried out under water to enhance the cooling rate of FSP, has a significant effect on microstructure refinement. In this study, microstructure and superplasticity of a Mg-Y-Nd alloy prepared by SFSP are investigated. The as-cast base material mainly consists of coarse a-Mg and net-shaped eutectic phases located at grain boundaries. After SFSP, microstructure of the alloy is mainly composed of fine-grained magnesium grains (∼1.3 μm) and homogeneously distributed second phase particles. The SFSP Mg-Y-Nd alloy shows relatively good high-strain-rate superplasticity, and its elongations are all above 500% within a temperature range of 708-758 K strained at 0.1 per second. The high-strain-rate superplasticity is attributed to the fine-grained microstructure and high thermal stability during superplastic deformation. Copyright © 2015 MS&T15®.

关键词： Ternary alloys

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Deformation behavior and microstructure evolution of 6063 alloy during hot compression

Deformation behavior and microstructure evolution of 6063 al...

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Chinese materials Conference, CMC 2017

作者： Yu, Zhu Hua Zhang, Da Tong Zhang, Wen Qiu, Cheng National Engineering Research Center of Near-Net-Shape Forming for Metallic Materials South China University of Technology Guangzhou510640 China

ISBN: (纸本)9783035712445

Hot compression tests of homogenized 6063 Al alloy were carried out in the temperatures range from 390℃ to 510℃ and strain rates from 1s-1 to 20s-1 on a Gleeble-3500 thermal simulation machine. The results showed that the flow stress decreased with increasing deformation temperature or decreasing strain rate. The dynamic softening effect was more obvious when the alloy was deformed at strain rate of 20 s-1. The Arrhenius-type constitutive equation with strain compensation can accurately describe the flow stress of 6063 aluminum alloy during hot compression. Shear bands appeared in grains interior when the alloy deformed at high strain rates, corresponding to high Zenner-Hollomon (Z) parameters. When deformed under the conditions with low Z parameters, the dynamic recrystallization started occurred. © 2018 Trans Tech Publications, Switzerland.

关键词： Constitutive equations

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