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Influence of Deformation on the Microstructure and Low-temperature Refining Behavior of Al-3.5P Master Alloy
Huan Qiao, Xiangzhen Zhu, Tong Gao, Yuying Wu, Xiangfa Liu
J. Mater. Sci. Technol.    2015, 31 (4): 391-396.   DOI: 10.1016/j.jmst.2014.09.010
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In this paper, the influence of deformation on the microstructure and low-temperature refining behavior of Al-3.5P master alloy was investigated. The results show that the average size of AlP particles can be reduced obviously from 15.3 μm to about 2.1 μm by deformation. However, it exhibits entirely opposite influence on refining performance when Al-3.5P master alloy was deformed at room temperature and high temperature, respectively. Only when Al-3.5P master alloy was subjected to thermal deformation, can an improvement of low-temperature refining performance be obtained. In this condition, primary Si in A390 alloy can be refined from 137 to 21 μm, making it a potential candidate for die casting production. A mechanism associated with the transformation of particle-matrix interface during deformation has been proposed and further experiment has been designed to validate it.
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Influence of Test Temperature on the Tensile Properties along the Thickness in a Friction Stir Welded Aluminum Alloy
Weifeng Xu, Jinhe Liu, Daolun Chen
J. Mater. Sci. Technol.    2015, 31 (9): 953-961.   DOI: http://dx.doi.org/10.1016/j.jmst.2015.07.005
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The aim of this study was to evaluate microstructures and the influence of test temperature on the tensile properties, strain hardening behavior and fracture characteristics of friction stir welded (FSWed) 2219-T62 aluminum alloy thick plate joints. A fine and equiaxed recrystallized grain structure had no significant change in grains at the top of weld nugget zone (WNZ) at a rotational rate of 500 r/min compared with 300 r/min, but the grains and second-phase particles at the middle of WNZ exhibited obvious coarsening. The yield strength, ultimate tensile strength and joint efficiency were observed to decrease with increasing test temperatures. However, the elongation presented a contrast trend. Compared with the middle and bottom slices, the top slice (216 and 342?MPa) had a higher strength and a lower elongation (8.5%) at different test temperatures. Hardening capacity and strain hardening exponent of bottom slices were higher than those of the top and middle slices. Both of them at room temperature (RT) were bigger than those at higher temperature (HT) and lower temperature (LT). The FSWed joints basically failed in the border area between the thermo-mechanical affected zone (TMAZ) and heat-affected zone (HAZ) of the top slice, and in the HAZ of the middle or bottom slices, while the fracture surfaces exhibited dimple fracture characteristics at different test temperatures.
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Preparation and Microstructural Characterization of Activated Carbon-Metal Oxide Hybrid Catalysts: New Insights into Reaction PathsA.
A. Barroso-Bogeat , M. Alexandre-Franco, C. Fern, ndez-Gonz, lez, V. G, mez-Serrano
J. Mater. Sci. Technol.    2015, 31 (8): 806-814.   DOI: 10.1016/j.jmst.2015.06.004
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In catalysis processes, activated carbon (AC) and metal oxides (MOs) are widely used either as catalysts or as catalyst supports because of their unique properties. A combination of AC and MO nanoparticles in a single hybrid material usually entails both chemical and microstructural changes, which may largely influence the potential catalytic suitability and performance of the resulting product. Here, the preparation of a wide series of AC-MO hybrid catalysts is studied. Three series of such catalysts are prepared by support first of MO (Al2O3, Fe2O3, SnO2, TiO2, WO3, and ZnO) precursors on a granular AC by wet impregnation and oven-drying at 120 °C, and by subsequent heat treatment at 200 or 850 °C in inert atmosphere. Both the chemical composition and microstructure are mainly investigated by powder X-ray diffraction. Yield and ash content are often strongly dependent on the MO precursor and heat treatment temperature, in particular for the Sn catalysts. With the temperature rise, trends are towards the transformation of metal hydroxides into metal oxides, crystallinity improvement, and occurrence of drastic composition changes, ultimately leading to the formation of metals in elemental state and even metal carbides. Reaction paths during the preparation are explored for various hybrid catalysts and new insights into them are provided.
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Effect of Rare Earth and Transition Metal Elements on the Glass Forming Ability of Mechanical Alloyed Al-TM-RE Based Amorphous Alloys
Ram S. Maurya, Tapas Laha
J. Mater. Sci. Technol.    2015, 31 (11): 1118-1124.   DOI: 10.1016/j.jmst.2015.09.007
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The present work aims to compare the amorphous phase forming ability of ternary and quaternary Al based alloys (Al86Ni8Y6, Al86Ni6Y6Co2, Al86Ni8La6 and Al86Ni8Y4.5La1.5) synthesized via mechanical alloying by varying the composition, i.e. fully or partially replacing rare earth (RE) and transition metal (TM) elements based on similar atomic radii and coordination number. X-ray diffraction and high resolution transmission electron microscopy study revealed that the amorphization process occurred through formation of various intermetallic phases and nanocrystalline FCC Al. Fully amorphous phase was obtained for the alloys not containing lanthanum, whereas the other alloys containing La showed partial amorphization with reappearance of intermetallic phases attributed to mechanical crystallization. Differential scanning calorimetry study confirmed better thermal stability with wider transformation temperature for the alloys without La.
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Shape Memory Effect, Thermal Expansion and Damping Property of Friction Stir Processed NiTip/Al Composite
D.R. Ni, J.J. Wang, Z.Y. Ma
J. Mater. Sci. Technol.    2016, 32 (2): 162-166.   DOI: 10.1016/j.jmst.2015.12.013
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NiTi particles reinforced aluminum (NiTip/Al) composite was prepared via friction stir processing, eliminating interfacial reaction and/or elemental diffusion. The NiTip in the composite maintained the intrinsic characteristic of a reversible thermoelastic phase transformation even after heat-treatment. The shape memory characteristic of the NiTip decreased the coefficient of thermal expansion of the Al matrix, and an apparent two-way shape memory effect was observed in the composite. The composite owned a good combination of adjustable damping and thermal physical properties.
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Microstructure and Mechanical Properties of Overcast 6101-6101 Wrought Al Alloy Joint by Squeeze Casting
Teng Liu, Qudong Wang, Yudong Sui, Qigui Wang
J. Mater. Sci. Technol.    2016, 32 (4): 298-305.   DOI: 10.1016/j.jmst.2015.11.020
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The wrought Al alloy-wrought Al alloy overcast joint was fabricated by casting liquid 6101 Al alloy onto 6101 Al extrusion bars and solidifying under applied pressure. The joint interfacial microstructure was investigated; the effect of applied pressure on the microstructure and mechanical properties was evaluated. The mechanism of joint formation and mechanical behaviors of both squeeze cast 6101 and 6101-6101 overcast joint material were analyzed. The results show that with the application of pressure during solidification process, wrought Al alloy 6101 could be cast directly into shape successfully. Excellent metallurgical bonding was then formed in the overcast joint by electro-plating 6101 solid insert with a layer of zinc coating, and a transition zone formed in the joint region. During the tensile test, the fracture occurs in the 6101 solid insert part with the ultimate tensile strength (UTS) of 200 MPa, indicating that the strength of the overcast joint is higher than 200 MPa, and the tensile strength of overcast joint material is independent on the magnitude of applied pressure. For Al-Al overcast joint material, if a clean and high strength joint is formed, the UTS and yield strength (YS) are determined by the material with the lower value, while for EL, the value is determined by the length proportion and the stress-strain behavior of both components.
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Effect of Fe, Si and Cooling Rate on the Formation of Fe- and Mn-rich Intermetallics in Al-5Mg-0.8Mn Alloy
Yulin Liu, Lei Luo, Chaofei Han, Liangyun Ou, Jijie Wang, Chunzhong Liu
J. Mater. Sci. Technol.    2016, 32 (4): 305-313.   DOI: 10.1016/j.jmst.2015.10.010
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The Fe- and Mn-rich intermetallics are of great effect on the mechanical properties of the AA5083 type alloy (Al-5Mg-0.8Mn). The effect of Fe, Si and cooling rate on the formation of the intermetallics were investigated by analyzing the microstructures of the alloys with different Fe and Si contents. The results indicated that increasing the Fe content resulted in the increase of the Al6(Fe,Mn) phase in both amount and size. In the alloys with high Fe content, the platelet-like Al6(Fe,Mn) compounds lined up and formed a band. Increasing the content of Si resulted in the increase of the Mg2Si phase which formed a network structure. Increasing the cooling rate significantly refined the intermetallics. However, increasing the cooling rate did not change the characteristic of the intermetallic compounds in the alloys with low or medium Si contents. For the alloys with high contents of Fe and Si under the condition of near-rapid cooling, the Fe- and Mn-rich intermetallic compound changed to the quaternary Al15(Fe,Mn)3Si phase and displayed a fine fish bone or Chinese script structure. The refinement of the intermetallics would allow higher tolerance of Fe and Si contents in the AA5083 alloy produced, for instance, via the continuous strip casting process.
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Effect of Decomposition Kinetics of Titanium Hydride on the Al Alloy Melt Foaming Process
Donghui Yang, Jianqing Chen, Hui Wang, Jinghua Jiang, Aibin Ma, Z.P. Lu
J. Mater. Sci. Technol.    2015, 31 (4): 361-368.   DOI: 10.1016/j.jmst.2014.09.013
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The gas released from the titanium hydride decomposition is one of the key factors to influence the Al alloy melt foaming process. In this study, a set of decomposition kinetic equations of titanium hydride was acquired by separating its temperature programmed decomposition (TPD) spectrum, which was acquired by a special designed TPD apparatus with argon used as carrier gas and thermal conductivity cell as the detector. According to these equations, the decomposition and hydrogen release characteristics of titanium hydride at a fixed/elevated temperature are described quantitatively, which can be applied to forecast the Al alloy melt foaming process and furnish the theoretical basis for fabrication of three-dimensional complex shaped Al alloy foam.
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Influence of Interfacial Bonding between Metal Droplets on Tensile Properties of 7075 Aluminum Billets by Additive Manufacturing Technique
Hansong Zuo, Hejun Li, Lehua Qi, Songyi Zhong
J. Mater. Sci. Technol.    2016, 32 (5): 485-488.   DOI: 10.1016/j.jmst.2016.03.004
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7075 aluminum billets were fabricated by micro droplet deposition manufacturing technique, and the influence of interfacial bonding between metal droplets on the tensile properties was studied. Three sets of samples were manufactured under different temperature conditions, and their mechanical properties were compared. The results show that the temperature of the metal droplets and substrate significantly affect the tensile strength of the sample. Moreover, with proper temperature setting, the 7075 aluminum billets manufactured by micro metal droplet deposition could achieve very good mechanical properties with a tensile strength of 373 MPa and an elongation of 9.95%, which are very similar to those of an extruded sample. Moreover, a metallurgical bonding diagram based on numerical calculations of interfacial temperature was established to predict the interfacial bonding state. In addition, the fracture morphologies of these specimens were observed. It is indicated that there was a significant transformation of failure mechanism with the improvement of metallurgical bonding, which agreed well with the numerical results.

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Devitrification-induced an Ultrahigh Strength Al-based Composite Maintaining Ductility
Dong Kan, Xiaopeng Li, Baijun Yang, Hongwang Yang, Jianqiang Wang
J. Mater. Sci. Technol.    2015, 31 (5): 489-492.   DOI: 10.1016/j.jmst.2014.07.022
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A new Al-based composite consisting of submicron-sized α-Al matrix embedded with precipitated intermetallic phases was developed by controlling the devitrification process of an Al-Ni-Y-Co-La amorphous alloy. Such a homogeneous composite structure presented an ultrahigh strength of about 1.34 GPa and a large compressive plastic strain up to 22%. The unique mechanical properties during compression are mainly attributed to the dislocation slip deformation of ductile α-Al matrix and the shear-induced refinement of strengthening intermetallic phases.
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