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Feng Li - One of the best experts on this subject based on the ideXlab platform.

  • Corrosion Behavior of AZ31 Magnesium Alloy Produced by Continuous Variable Cross Section Direct Extrusion
    Journal of Materials Engineering and Performance, 2019
    Co-Authors: Wen Kang, Feng Li, Xue Wen Li, Wen Bin Fang
    Abstract:

    In order to study the corrosion behavior of magnesium alloys of high performance in the simulated seawater by continuous variable cross section Direct Extrusion (CVCDE), an electrochemical method and weight loss method were used to study the difference between AZ31 magnesium alloys produced by CVCDE with different numbers of interim dies to examine the electrochemical corrosion behavior and corrosion rate at 3.5 wt.% NaCl solution in this paper. Scanning electron microscopy and x-ray diffraction were used to analyze the morphology of corrosion surfaces and the composition of the corrosion products of samples soaked for different times. The results show that after CVCDE with different numbers of interim dies, the size of the microstructure is refined gradually, and the grain orientation is also different; with the increase in the number of interim dies, the thermodynamic corrosion tendencies are different, and the corrosion resistance of samples extruded by conventional Extrusion is relatively good; the charge transfer and material transfer process are the two main factors affecting the corrosion rate, which determines the Direction of the electrochemical reaction; the corrosion form of the sample extruded by CVCDE is the local corrosion which is the filiform corrosion and pitting corrosion, and the corrosion product is mainly water-insoluble Mg(OH)2.

  • microstructural characteristics of az31 magnesium alloy processed by continuous variable cross section Direct Extrusion cvcde part 1 texture evolution
    JOM, 2018
    Co-Authors: Xu Bo Li, Feng Li, Xue Wen Li
    Abstract:

    Extrusion products with ideal microstructure and mechanical properties can be obtained by precise design of the mold cavity structure. In this study, two interim dies were taken as a sample to investigate the texture of typical locations of AZ31 magnesium alloy produced by continuous variable cross-section Direct Extrusion (CVCDE). The results show that grains were refined significantly after the material passed through the continuous variable mold cavity. Stronger Extrusion fiber texture formed during the CVCDE process, and the texture type of the Extrusion product transformed from {0001}〈10–10〉 deformation texture to a mixture of {0001}〈10-10〉 deformation texture and {0001}〈11–20〉 recrystallization texture. During the Extrusion process, the c-axis of the majority of grains deflected under the action of external forces and tended to become parallel to the Direction of the external forces. Therefore, the value of the Schmid factor, which represents the grain orientation, became smaller and the grains were in hard orientation, making further slip difficult.

  • microstructural characteristics of az31 magnesium alloy processed by continuous variable cross section Direct Extrusion cvcde part 2 dynamic recrystallization
    JOM, 2018
    Co-Authors: Xu Bo Li, Feng Li, Xue Wen Li
    Abstract:

    Through the precise design of the mold cavity structure, the ideal microstructure and mechanical property of the Extrusion product can be obtained. In this article, the two interim dies were taken as a sample to study the microstructure of typical locations of AZ31 magnesium alloy produced by continuous variable cross-section Direct Extrusion (CVCDE). The results showed that the grains were refined significantly and became more homogeneous after the material passed through the continuous variable mold cavity. By contrast of different locations of the Extrusion product, the dynamic recrystallization was sufficient and the proportion of recrystallization grains was the largest at the outlet position of the mold die.

  • properties of rolled az31 magnesium alloy sheet fabricated by continuous variable cross section Direct Extrusion
    Journal of Materials Engineering and Performance, 2018
    Co-Authors: Feng Li, Xue Wen Li
    Abstract:

    Rolling is currently a widely used method for manufacturing and processing high-performance magnesium alloy sheets and has received widespread attention in recent years. Here, we combined continuous variable cross-section Direct Extrusion (CVCDE) and rolling processes. The microstructure and mechanical properties of the resulting sheets rolled at different temperatures from CVCDE extrudate were investigated by optical microscopy, scanning electron microscope, transmission electron microscopy and electron backscatter diffraction. The results showed that a fine-grained microstructure was present with an average grain size of 3.62 μm in sheets rolled from CVCDE extrudate at 623 K. Dynamic recrystallization and a large strain were induced by the multi-pass rolling, which resulted in grain refinement. In the 573-673 K range, the yield strength, tensile strength and elongation initially increased and then declined as the CVCDE temperature increased. The above results provide an important scientific basis of processing, manufacturing and the active control on microstructure and property for high-performance magnesium alloy sheet.

  • effect of different temperatures on deformation characteristics of az31 magnesium alloy by continuous variable cross section Direct Extrusion
    The International Journal of Advanced Manufacturing Technology, 2018
    Co-Authors: Xu Bo Li, Feng Li, Xue Wen Li
    Abstract:

    This paper based on the research of the different temperatures of AZ31 magnesium alloy by continuous variable cross-section Direct Extrusion (CVCDE) studied the effect of forming temperature on the deformation characteristics of magnesium alloy by CVCDE. It was found that the average size of grains and the proportion of large angle grain boundaries in microstructure increased obviously with the increase of forming temperature, which showed dynamic recrystallization has been relatively adequate. Because the dislocation density inside the grains was higher and the texture was weakened obviously at 623 K by compared with other temperatures, the yield strength and elongation increased at first and then decreased with the increase of temperature. This paper reveals the deformation mechanism of AZ31 magnesium alloy by CVCDE, which can provide scientific guidance for the development of magnesium alloy Extrusion products with high property.

X Zeng - One of the best experts on this subject based on the ideXlab platform.

  • microstructural characteristics and deformation of magnesium alloy az31 produced by continuous variable cross section Direct Extrusion
    Journal of Materials Science & Technology, 2017
    Co-Authors: Hongwei Jiang, Feng Li, X Zeng
    Abstract:

    Abstract Magnesium (Mg) alloy AZ31 was produced by continuous variable cross-section Direct Extrusion (CVCDE) to study its deformation behavior. Metallographic microscopy (OM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) were used to observe the variations in microstructure and fracture morphology of Mg alloy AZ31 as a function of processing methods. The results reveal that grains of Mg alloy AZ31 were refined and their microstructure was homogenized by CVCDE. The recrystallization in Mg alloy AZ31 produced by CVCDE with 2 interim dies was more complete than that produced by conventional Extrusion (CE) and CVCDE with 1 interim die, and the grains were finer and more uniform. Plasticity of the AZ31 alloy was improved. Fracture mode was evolved from a combination of ductility and brittleness to a sole ductile form. In summary, a CVCDE mold structure with 2 interim dies can improve microstructure, plasticity, and toughness of Mg alloy AZ31.

  • investigation of 7a09 aluminum alloy prepared by continuous variable cross section Direct Extrusion cvcde
    The International Journal of Advanced Manufacturing Technology, 2016
    Co-Authors: Feng Li, Hong Bin Wu, X Zeng
    Abstract:

    Preparation-forming is a common method to get high-performance alloy products, but lots of shortcomings exist in this method, such as complex and long process, high costs, and so on. As a new severe plastic deformation technology, continuous variable cross-section Direct Extrusion (CVCDE) is used to solve these problems. Taking 7A09 aluminum alloy, for example, the research result of CVCDE process shows that actual material flow distance is longer than conventional Extrusion, and the axial stress on product surface in the die orifice is also significantly decreased. At the same time, the material flows through die cavity sequentially and suffers “upsetting-Extrusion-upsetting” continuous loading, which will result in a severe deformation. By analysis of the microstructure and mechanical properties of 7A09 aluminum alloy was obtained under different conditions, it can be known that the grains become smaller and more round, and the uniformity gets also improved after CVCDE. Compared with conventional Extrusion, the grain refinement of CVCDE with one and two interim dies increased by 22.4 and 41.5 %, respectively, and tensile strength and elongation also increase. To sum up, CVCDE with high efficiency, low consumption, short process, and other unique advantages in obtaining high-performance alloy products will be certainly raised wide concern.

  • effect of local strains on the texture and mechanical properties of az31 magnesium alloy produced by continuous variable cross section Direct Extrusion cvcde
    Materials & Design, 2015
    Co-Authors: Feng Li, X Zeng, Qiang Chen
    Abstract:

    Abstract Three different mold structures were designed by changing the parameters of mold cavity to study the effect of local strains on the texture and mechanical properties of AZ31 magnesium alloy produced by continuous variable cross-section Direct Extrusion (CVCDE) with 2 interim dies. Microstructure and texture evolution of AZ31 magnesium alloy after CVCDE were studied by electron backscatter diffraction (EBSD). Mechanical properties were determined by uniaxial tensile tests along Extrusion Direction (ED) at room temperature. Due to the differences of local strains among the three schemes, the microstructure of Scheme 1 was the most uniform and the average grain size of Scheme 1 was the smallest. Meanwhile, tensile strength and elongation of Scheme 1 were the highest. Different textures had been formed in the three schemes. Lots of extension twins {10–12} (86° ) occurred in the products of the three schemes. The main deformation modes of Scheme 1 and Scheme 2 were slip and twinning. However, slip was dominant in Scheme 3. The deformation modes provided an essential basic for the design of CVCDE mold structure with more interim dies.

  • microstructure of az31 magnesium alloy produced by continuous variable cross section Direct Extrusion cvcde
    Materials Letters, 2014
    Co-Authors: Feng Li, X Zeng, N Bian
    Abstract:

    Abstract In order to study the effect of a new Severe Plastic Deformation (SPD) technique-continuous variable cross-section Direct Extrusion (CVCDE) on improving the mechanical properties of magnesium alloy, electronic backscattered diffraction (EBSD) was employed to investigate the microstructure and texture of CVCDEed AZ31 magnesium alloy. Compared with conventional Extrusion (CE), CVCDE can increase the accumulated strain without changing the total Extrusion ratio during Extrusion process. Under the effect of CVCDE, coarse grains can be further sheared up to refined grains and the number of dynamic recrystallization grains increases. At the same time, this method can significantly weaken basal plane texture and improve tensile strength and elongation of CVCDEed product, which provides an effective way to produce excellent performance magnesium alloys.

Dongquan Yu - One of the best experts on this subject based on the ideXlab platform.

  • Improved viscoelastic, thermal, and mechanical properties of in situ microfibrillar polypropylene/polyamide 6,6 composites via Direct Extrusion using a triple-screw extruder
    RSC Advances, 2017
    Co-Authors: Ying Huang, Yadong He, Weidan Ding, Kunxiao Yang, Dongquan Yu
    Abstract:

    In this work, a triangle arrayed triple-screw extruder (TTSE) was used to prepare in situ polypropylene/polyamide 6,6 (PP/PA66) microfibrillar composites (MFCs) by Direct Extrusion at a processing temperature between the melting points of the two phases. The dispersed phase, PA66 particles, deformed, merged and was stretched into fibrils under the alternating shearing and extensional flow field in the TTSE. The fibrillar morphology was controlled through adjusting the PA66 content and processing parameters (temperature and screw speed). Dynamic oscillatory shear rheological properties and extensional viscosity of PP/PA66 microfibrils with different aspect ratio were studied. The obtained results showed that the storage modulus and complex viscosity of PP/PA66 MFCs were improved with increasing fibrillar aspect ratio. Meanwhile, the loss tangent tan δ value decreased and the radius of the Cole–Cole plot circle increased with an increase in fibrillar aspect ratio. The PP/PA66 MFCs exhibited a pseudo-solid or gel-like behavior. The gel point concentration, which was determined by the Winter–Chambon criterion, decreased with the increasing fibrillar aspect ratio due to the increased interfacial area and enhanced entangled network structure. Additionally, high-aspect-ratio PA66 fibrils have dramatically improved PP's melting temperature, crystallization kinetics, and mechanical properties.

  • improved viscoelastic thermal and mechanical properties of in situ microfibrillar polypropylene polyamide 6 6 composites via Direct Extrusion using a triple screw extruder
    RSC Advances, 2017
    Co-Authors: Ying Huang, Yadong He, Weidan Ding, Kunxiao Yang, Dongquan Yu
    Abstract:

    In this work, a triangle arrayed triple-screw extruder (TTSE) was used to prepare in situ polypropylene/polyamide 6,6 (PP/PA66) microfibrillar composites (MFCs) by Direct Extrusion at a processing temperature between the melting points of the two phases. The dispersed phase, PA66 particles, deformed, merged and was stretched into fibrils under the alternating shearing and extensional flow field in the TTSE. The fibrillar morphology was controlled through adjusting the PA66 content and processing parameters (temperature and screw speed). Dynamic oscillatory shear rheological properties and extensional viscosity of PP/PA66 microfibrils with different aspect ratio were studied. The obtained results showed that the storage modulus and complex viscosity of PP/PA66 MFCs were improved with increasing fibrillar aspect ratio. Meanwhile, the loss tangent tan δ value decreased and the radius of the Cole–Cole plot circle increased with an increase in fibrillar aspect ratio. The PP/PA66 MFCs exhibited a pseudo-solid or gel-like behavior. The gel point concentration, which was determined by the Winter–Chambon criterion, decreased with the increasing fibrillar aspect ratio due to the increased interfacial area and enhanced entangled network structure. Additionally, high-aspect-ratio PA66 fibrils have dramatically improved PP's melting temperature, crystallization kinetics, and mechanical properties.

Guillermo Requena - One of the best experts on this subject based on the ideXlab platform.

  • ecap vs Direct Extrusion techniques for consolidation of ultra fine al particles
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2009
    Co-Authors: Martin Balog, Frantisek Simancik, Otto Bajana, Guillermo Requena
    Abstract:

    Abstract In this study equal channel angular pressing (ECAP) with accommodated backpressure was used as a technique for consolidation of fine atomized monocrystalline ( d 50  = 1.3 μm) Al 99.7% powder. The effect of ECAP on consolidation behavior of powder, microstructure and mechanical properties of subsequent compacts in comparison to conventional Direct Extrusion (DE) is presented. Consolidation was realized via simple processing route, where complicated step of gastight encapsulating of vacuumed powder was avoided. Both ECAPed and extruded compacts featured sound ultra-fine grained (UFG) microstructures, consisting of elongated grains of intensively sheared powder particles. Grain boundaries of compacts were stabilized with homogenously redistributed nano-scale particles of torn oxide surface layers of initial Al powder particles. UFG character of ECAPed and extruded compacts resulted in their relatively high strengths at room temperature (up to R m  = 316 MPa) and especially at elevated temperatures (up to R m  = 188 MPa at 300 °C). Inferior ductility of ECAPed compacts ( A ∼2%) compared to extrudants ( A ∼10%) was due to their disadvantageous microstructure texture reflecting deformation along ECAP shearing plane. Owing to grain pinning effect of broken oxide particles, compacts exhibited excellent structural stability with no major microstructural changes and deterioration of mechanical properties determined after 350 °C/20 h annealing. The trade-off between simple processing route and effect of residual porosity on high temperature mechanical properties is discussed.

  • ECAP vs. Direct Extrusion—Techniques for consolidation of ultra-fine Al particles
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2009
    Co-Authors: Martin Balog, Frantisek Simancik, Otto Bajana, Guillermo Requena
    Abstract:

    Abstract In this study equal channel angular pressing (ECAP) with accommodated backpressure was used as a technique for consolidation of fine atomized monocrystalline ( d 50  = 1.3 μm) Al 99.7% powder. The effect of ECAP on consolidation behavior of powder, microstructure and mechanical properties of subsequent compacts in comparison to conventional Direct Extrusion (DE) is presented. Consolidation was realized via simple processing route, where complicated step of gastight encapsulating of vacuumed powder was avoided. Both ECAPed and extruded compacts featured sound ultra-fine grained (UFG) microstructures, consisting of elongated grains of intensively sheared powder particles. Grain boundaries of compacts were stabilized with homogenously redistributed nano-scale particles of torn oxide surface layers of initial Al powder particles. UFG character of ECAPed and extruded compacts resulted in their relatively high strengths at room temperature (up to R m  = 316 MPa) and especially at elevated temperatures (up to R m  = 188 MPa at 300 °C). Inferior ductility of ECAPed compacts ( A ∼2%) compared to extrudants ( A ∼10%) was due to their disadvantageous microstructure texture reflecting deformation along ECAP shearing plane. Owing to grain pinning effect of broken oxide particles, compacts exhibited excellent structural stability with no major microstructural changes and deterioration of mechanical properties determined after 350 °C/20 h annealing. The trade-off between simple processing route and effect of residual porosity on high temperature mechanical properties is discussed.

Hong Jun Hu - One of the best experts on this subject based on the ideXlab platform.