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China Foundry
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ISSN (Print) 1672-6421 - ISSN (Online) 2365-9459
Published by Springer-Verlag Homepage  [2352 journals]
  • Microstructure and wear characteristics of ATZ ceramic particle reinforced
           gray iron matrix surface composites

    • Authors: Xue Ma; Liang-feng Li; Fan Zhang; Zu-hua Zhang; Hao Wang; En-ze Wang
      Pages: 167 - 172
      Abstract: The alumina toughened zirconia (ATZ) ceramic particle reinforced gray iron matrix surface composite was successfully manufactured by pressureless infiltration. The porous preform played a key role in the infiltrating progress. The microstructure was observed by scanning electron microscopy (SEM); the phase constitutions was analyzed by X-ray diffraction (XRD); and the hardness and wear resistance of selected specimens were tested by hardness testing machine and abrasion testing machine, respectively. The addition of high carbon ferrochromium powders leads to the formation of white iron during solidification. The wear volume loss rates of ATZ ceramic particle reinforced gray iron matrix surface composite decreases first, and then tends to be stable. The wear resistance of the composite is 2.7 times higher than that of gray iron matrix. The reason is a combination of the surface hardness increase of gray iron matrix and ATZ ceramic particles and alloy carbides protecting effect on gray iron matrix.
      PubDate: 2018-05-01
      DOI: 10.1007/s41230-018-7211-6
      Issue No: Vol. 15, No. 3 (2018)
  • Effects of austempering temperature on microstructure and surface residual
           stress of carbidic austempered ductile iron (CADI) grinding balls

    • Authors: Jin-hai Liu; Peng Xiong; Bin-guo Fu; Wei-ting Yang; Xue-bo Zhao; Zi-ang Han; Guo-lu Li
      Pages: 173 - 181
      Abstract: The effects of austempering temperature on microstructure and surface residual stress of carbidic austempered ductile iron (CADI) grinding balls were systematically investigated in this work. The microstructures were oberserved by optical metallography and analyized by X-ray diffraction. The surface residual stress measured by the cutting method is mainly composed of thermal stress and phase transformation stress. The thermal stress in grinding balls was determined by ANSYS simulation technique, and the surface phase transformation stress was obtained by subtracting the simulated surface thermal stress from the measured surface residual stress. Results show that all microstructures consist of ausferrite, white-bright zones (mixture of martensite and austenite), nodular graphite, and carbides. The distribution of ausferrite shows uniform. With the increase of austempering temperature, the volume fraction and carbon content of austenite increase, whereas the amount of white-bright zone decreases. In addition, the surface residual stress increases with the increase of austempering temperature. Only the tension exists at the austempering temperature of 200 °C, and the pressure exists at the austempering temperature of 220–260 °C. The thermal stress changes from the tension on the inside with the radius of 0–35 mm to the pressure on the outside with the radius of 35–62.5 mm, and the stress balance state presents at the radius of 35 mm. It is also found that the transformation stress is related to the content of carbon-rich austenite, and will reduce by 5.03 MPa accompanied with 1vol.% increase of the austenite. The thermal compressive stress and the transformation tensile stress on the surface both decrease with the increase of the austempering temperature.
      PubDate: 2018-05-01
      DOI: 10.1007/s41230-018-7245-9
      Issue No: Vol. 15, No. 3 (2018)
  • Effect of sigma phase precipitation on microstructure and properties of
           cast ZG0Cr26Ni5Mo3Cu3 duplex stainless steel under different heat

    • Authors: Ze-hua Zhu; Wei-dong Zhang; Xiao-hui Tu; Xiao-jian Wang; Wei Li
      Pages: 182 - 188
      Abstract: ZG0Cr26Ni5Mo3Cu3 Duplex Stainless Steel (DSS) was solution treated at 1,060 ºC for 3 h, followed by water cooling. Tempering treatments were conducted at 720, 750 and 780 ºC, respectively, for 16 h, followed by air cooling. The microstructures of ZG0Cr26Ni5Mo3Cu3 duplex stainless steel samples treated at different tempering temperatures were observed by scanning electron microscope (SEM) and energy dispersal spectroscopy (EDS), and the phase consitutions were analyzed using X-ray diffraction (XRD). The effects of the precipitation of sigma (σ) phase on the duplex phase percentage, hardness, impact toughness and corrosion resistance of the DSS were studied. Results showed that microstructures of ZG0Cr26Ni5Mo3Cu3 after solution treatment consists of ferrite (α) phase and austenite (γ) phase; after being tempered at different temperatures, σ phase appeared due to a eutectoid-type reaction of α→σ+γ2 during tempering treatment. It was observed that σ phase distributed along the grain boundary. The volume fraction of σ and γ phases increased with increasing tempering temperature in the range of 720 to 780 ºC, whereas the volume fraction of α phase showed the opposite trend. When the percentage of σ phase increased, the hardness of steel also increased. In the solution treated steel, hardness was measured to be only 244.0 HB, because σ phase did not appear. However, it increased to 391.8 HB when the DSS was tempered at 780 ºC because a great of deal of σ phase appeared. The impact toughness and corrosion resistance of DSS decreased when the percentage of σ phase increased.
      PubDate: 2018-05-01
      DOI: 10.1007/s41230-018-7226-z
      Issue No: Vol. 15, No. 3 (2018)
  • Effects of alloy elements on ductility and thermal conductivity of
           compacted graphite iron

    • Authors: Dong-mei Xu; Gui-quan Wang; Xiang Chen; Yan-xiang Li; Yuan Liu; Hua-wei Zhang
      Pages: 189 - 195
      Abstract: The influence of Si, Sn, Mo and Ni on the ductility and thermal conductivity of compacted graphite iron (CGI) was investigated. Metallographic observation and Differential Scanning Calorimetry (DSC) experiments were carried out to analyze the roles of various additions in the eutectoid reaction. The experimental results showed that the ductility of CGI is proportional to the ferrite fraction, so moderate Si content could dramatically improve the ductility by increasing the ferrite fraction. DSC measurements showed that Mo has moderate inhibition on eutectoid transformation during both the heating and cooling processes, while the sample without Sn obviously broadens the three-phase region. Vermicularity and ferrite are known to improve thermal conductivity, and the former plays a more important role. Besides, among the alloy elements investigated, Sn has the greatest negative effect on conductivity, followed by Ni and Mo having the smallest effects.
      PubDate: 2018-05-01
      DOI: 10.1007/s41230-018-8055-9
      Issue No: Vol. 15, No. 3 (2018)
  • Influence of pouring methods on filling process, microstructure and
           mechanical properties of AZ91 Mg alloy pipe by horizontal centrifugal

    • Authors: Xue-feng Zhu; Bao-yi Yu; Li Zheng; Bo-ning Yu; Qiang Li; Shu-ning Lü; Hao Zhang
      Pages: 196 - 202
      Abstract: Pouring position as the input heat source has great influence on the temperature field evolution. In this study, the Flow3D simulation software was applied to investigate the influence of pouring methods (with fixed or moving pouring channel) on AZ91 Mg alloy horizontal centrifugal casting (HCC) process. The simulation results show that the moving pouring channel method can effectively increase the cooling rate and formability of casting pipe. The casting experiment shows that an AZ91 Mg alloy casting pipe with homogeneous microstructure and clear contour was obtained by the moving pouring channel method, and the grain size of the casting pipe is significantly decreased. Meanwhile, serious macro-segregation appeared in the AZ91 casting pipe by the fixed pouring channel HCC process. Compared with the fixed pouring channel, the moving pouring channel can remarkably improve the ultimate tensile strength and elongation of the AZ91 HCC pipe from 142.2 MPa to 201.5 MPa and 6.2% to 6.7%, respectively.
      PubDate: 2018-05-01
      DOI: 10.1007/s41230-018-7256-6
      Issue No: Vol. 15, No. 3 (2018)
  • Nano-SiC P particles distribution and mechanical properties of Al-matrix
           composites prepared by stir casting and ultrasonic treatment

    • Authors: Shu-sen Wu; Du Yuan; Shu-lin Lü; Kun Hu; Ping An
      Pages: 203 - 209
      Abstract: Nano-ceramic particles are generally difficult to add into molten metal because of poor wettability. Nano-SiC particles reinforced A356 aluminum alloy composites were prepared by a new complex process, i.e., a molten-metal process combined with high energy ball milling and ultrasonic vibration methods. The nano particles were β-SiCp with an average diameter of 40 nm, and pre-oxidized at about 850 °C to form an oxide layer with a thickness of approximately 3 nm. The mm-sized composite granules containing nano-SiCp were firstly produced by milling the mixture of oxidized nano-SiCp and pure Al powders, and then were remelted in the matrix-metal melt with mechanical stirring and treated by ultrasonic vibration to prepare the composite. SEM analysis results show that the nano-SiC particles are distributed uniformly in the matrix and no serious agglomeration is observed. The tensile strength and elongation of the composite with 2wt.% nano-SiCp in as-cast state are 226 MPa and 5.5%, improved by 20% and 44%, respectively, compared with the A356 alloy.
      PubDate: 2018-05-01
      DOI: 10.1007/s41230-018-8009-2
      Issue No: Vol. 15, No. 3 (2018)
  • Controlled cooling of an aluminum alloy casting based on 3D printed rib
           reinforced shell mold

    • Authors: Hao-long Shangguan; Jin-wu Kang; Ji-hao Yi; Cheng-yang Deng; Yong-yi Hu; Tao Huang
      Pages: 210 - 215
      Abstract: 3D printing technology has been used for sand molding and core printing, but they simply substitute the traditional molding and core making method without changing the shape or size of the sand mold (core) and their dense structure. In this study, a new type of hollow mold based on 3D printing is presented. The new type of mold is a rib reinforced thickness-varying shell mold. This mold design can realize the controlled cooling of castings, i.e., different cooling rates at different areas, and improve the temperature uniformity of a casting after its solidification. Therefore, the performance of castings can be improved and their residual stress and deformation can be reduced. This kind of new mold was applied to a stress frame of A356 aluminum alloy. The 3D printed rib reinforced thickness-varying shell mold was compared with the traditional dense mold, and the castings obtained by these two kinds of molds were also compared. The experimental results showed that the rib reinforced shell mold increased the cooling rate of the casting by 30%, tensile strength by 17%, yield strength by 11%, elongation by 67%, and decreased its deformation by 43%, while sand consumption was greatly reduced by 90%.
      PubDate: 2018-05-01
      DOI: 10.1007/s41230-018-7252-x
      Issue No: Vol. 15, No. 3 (2018)
  • Deformation and fracture of a Zr-Al-Cu metallic glass ribbon under tension
           near glass transition temperature

    • Authors: Xue-feng Gao; Na Ge; Fu-yu Dong; Rui-chun Wang; Hong-wang Yang
      Pages: 216 - 221
      Abstract: The high temperature tensile and fracture behavior of Zr50Al40Cu10 metallic glass at the temperature range in the vicinity of glass transition were investigated. Tensile tests were carried out at room temperature, 350–420 °C, and in the supercooled liquid region temperature range, respectively. Obvious plastic deformation was initiated at temperature about 80 °C lower than the glass transition temperature. The ultimate tensile strength decreases with the increase of testing temperature and the ductility increases with temperature. At temperature higher than Tg, viscous flow of Non-Newtonian fluid led to super plastic deformation behavior. The deformation process under tension was inhomogeneous, and remarkable serrations were observed on the stress-strain curve near glass transition temperature.
      PubDate: 2018-05-01
      DOI: 10.1007/s41230-018-8054-x
      Issue No: Vol. 15, No. 3 (2018)
  • Microstructure evolution and liquid phase separation in Ta-O
           hypermonotectic melts during laser-cladding

    • Authors: Hai-ou Yang; Meng Wang; Xin Lin; Wei-dong Huang
      Pages: 222 - 227
      Abstract: A three-layer Ta2O5-containing coating was successfully fabricated by laser cladding on a pure Ta substrate. The maximum thickness of such a coating is about 1.6 mm. The microstructure, phase constitution and elemental distribution in the coating were investigated. Results show that the coating has been metallurgically bonded to the Ta substrate and the microstructure exhibits a graded change along the deposition direction from Ta substrate to the top of coating. In the layers I and II of the graded coating, the microstructure evolution can be confirmed as a result of hypomonotectic reaction, but in the layer III it was formed by hypermonotectic reaction. At the top of coating, the microstructure was still homogeneous although liquid phase separation had occurred, which can be attributed to the fact that the O-rich droplets do not have enough time to float at high cooling rate. The theoretical calculation results show that during laser cladding, the solidification time of the melt pool was less than 0.1 s, which fits well with the results from the experiment.
      PubDate: 2018-05-01
      DOI: 10.1007/s41230-018-8059-5
      Issue No: Vol. 15, No. 3 (2018)
  • Niobium addition effect in molds at last cooling step on EN-GJL250 gray
           cast iron: Microstructural changes and electrochemical behavior

    • Authors: M. O. Azzoug; N. Boutarek-Zaourar; D. Aboudi; N. Madaoui; E. Mossang; S. Chentouf
      Pages: 228 - 235
      Abstract: The purpose of this study was to determine the impact of niobium addition as an inoculation element on the microstructure and electrochemical properties of EN-FGL250 gray cast iron. Niobium additions are in a powder form and have a 0.5 mm particle size at dfferent proportions of 1wt.% and 3wt.%. The addition was done during casting of the metal in the mold at the last cooling step of the melt cast iron. These additions have a significant impact on the phenomenon of solidification as the metal powder deposited in the sand molds creates new centers of germination and absorbs a lot of heat. The cooling rate directly affects the microstructure and electrochemical behavior. This is confirmed by SEM observations and electrochemical tests. Furthermore, the addition of niobium transforms the microstructure of gray cast iron from cellular structure into totally dendritic structure. As a consequence, the niobium addition affected the shape and size of graphite, thus considerably reducing the corrosion current density by increasing the polarization resistance Rp.
      PubDate: 2018-05-01
      DOI: 10.1007/s41230-018-8007-4
      Issue No: Vol. 15, No. 3 (2018)
  • Research progress on refractory composition and deformability of shell
           molds for TiAl alloy castings

    • Authors: Chun-ling Bao; Shuang-qi Zhang; Yu-yan Ren; You-wei Zhang; Hua-sheng Xie; Jun Zhao
      Pages: 1 - 10
      Abstract: At present, most TiAl components are produced by an investment casting process. Environmental and economic pressures have, however, resulted in a need for the industry to improve the current casting quality, reduce manufacturing costs and explore new markets for the process. Currently, the main problems for investment casting of TiAl alloys are cracks, porosities, and surface defects. To solve these problems, many studies have been conducted around the world, and it is found that casting defects can be reduced by improving composition and properties of the shell molds. It is important to make a summary for the related research progress for quality improvement of TiAl castings. So, the development on refractory composition of shell molds for TiAl alloy investment castings was reviewed, and research progress on deformability of shell mold for TiAl alloy castings both at home and abroad in recent years was introduced. The existing methods for deformability characterization and methods for improving the deformability of shell molds were summarized and discussed. The updated advancement in numerical simulation of TiAl alloy investment casting was presented, showing the necessity for considering the deformability of shell mold during simulation. Finally, possible research points for future studies on deformability of shell mold for TiAl alloy investment casting were proposed.
      PubDate: 2018-01-01
      DOI: 10.1007/s41230-018-7022-9
      Issue No: Vol. 15, No. 1 (2018)
  • A new fast heat treatment process for cast A356 alloy motorcycle wheel

    • Authors: Shi-ping Lu; Rui Du; Jian-ping Liu; Lin-can Chen; Shu-sen Wu
      Pages: 11 - 16
      Abstract: The normal T6 heat treatment process for cast A356 alloy generally requires about 15 h. This long-period procedure increases greatly the manufacturing cost and decreases the productivity in practical production. In this study, a new short-time heat treatment process with only 30 min solution time at 540 °C was developed for the production of motorcycle wheel hubs in order to reduce heat treatment time. Comparisons on microstructure evaluation and mechanical properties, such as tensile strength and ductility, were made between this new fast process and the conventional T6 heat treatment. The results revealed that this new heat treatment process enabled the spheroidization of the eutectic silicon thoroughly, while minimizing the growth of eutectic silicon. The A356 alloy after this new short-time heat treatment shows nearly equal mechanical properties compared with the same alloy heat treated in a normal T6 heat treatment. This investigation makes it possible to significantly improve the efficiency of heat treatment on A356 alloy and, at the same time, improve the mechanical properties of the alloy.
      PubDate: 2018-01-01
      DOI: 10.1007/s41230-018-7058-x
      Issue No: Vol. 15, No. 1 (2018)
  • Effect of Cr on microstructure and oxidation behavior of TiAl-based alloy
           with high Nb

    • Authors: Zhu-Hang Jiang; Cheng-Zhi Zhao; Jiao-Jiao Yu; He-Xin Zhang; Zhi-Ming Li
      Pages: 17 - 22
      Abstract: Three novel multi-microalloying TiAl-based alloys containing high Nb were designed and fabricated. Thermogravimetric method was applied to investigate the influence of Cr on the oxidation behavior of high Nb-TiAl alloy at 1,073 K for 200 h in laboratory air. The 2at.% and 4at.% Cr were added into the alloy, (respectively named 2Cr and 4Cr compared to the Cr-free ternary alloy, 0Cr alloy). The alloys’ microstructure and composition as well as the composition distribution of the oxidation scale were analyzed by means of Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and X-Ray Diffractometry (XRD). The results show that the addition of Cr decreases the grain size of the Nb-TiAl alloy and leads to a transformation from a fully lamellar structure to a nearly fully lamellar structure. When oxidized at 1,073 K for 200 h, the oxidized mass gain of the alloy increases with an increase in Cr addition amount in the first 100 h and decreases in the last 100 h. With the increase of Cr content, the oxidation surface turns compact but uneven in morphology, which may affect the oxidation resistance of the alloy by increasing the peeling off risk of the oxidation layer at friction conditions.
      PubDate: 2018-01-01
      DOI: 10.1007/s41230-018-7020-y
      Issue No: Vol. 15, No. 1 (2018)
  • Effect of SiO 2 concentration in silica sol on interface reaction during
           titanium alloy investment casting

    • Authors: Ya-meng Wei; Ke-hui Hu; Zhi-gang Lu
      Pages: 23 - 30
      Abstract: Using silica sol as a binder for titanium investment casting is very attractive due to its good stability and reasonable cost as compared with yttrium sol and zirconium sol. However, the mechanism of interface reaction in the related system remains unclear. In this investigation, the interface reaction between Y2O3-SiO2 (Y-Si) shell mold and titanium alloys was studied. A group of shell molds were prepared by using Y2O3 sand and silica sol with different contents of SiO2. Ti-6Al-4V alloy was cast under vacuum by gravity casting through cold crucible induction melting (CCIM) method. Scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) were employed to characterize the micromorphology and composition of the reaction area, respectively. X-ray photoelectron spectroscopy (XPS) was used to confirm the valence state of relevant elements. White light interferometer (WLI) was used to obtain the surface topography of Y-Si shells. The results show that the thickness of reaction layers is below 3 μm when the SiO2 content of silica sol is below 20wt.%. Whereas, when the SiO2 content increases to 25wt.%, the thickness of the reaction layer increases sharply to about 15 μm. There is a good balance between chemical inertness and mechanical performance when the SiO2 content is between 15 and 20wt.%. Moreover, it was found that the distribution of SiO2 and the roughness at the surface of the shell are the key factors that determine the level of reaction.
      PubDate: 2018-01-01
      DOI: 10.1007/s41230-018-7066-x
      Issue No: Vol. 15, No. 1 (2018)
  • Microstructure and properties of TP2 copper tube with La microalloying by
           horizontal continuous casting

    • Authors: Jin-hu Wu; Shi-hong Zhang; Yan Chen; Hai-hong Li; Hong-wu Song; Ming Cheng; Jin-song Liu
      Pages: 31 - 36
      Abstract: The TP2 copper tube was prepared with La microalloying by horizontal continuous casting (HCC). The absorptivity of La and its effects on microstructure, tensile and corrosion properties of HCC TP2 copper tube were studied by means of the inductively coupled plasma optical emission spectrometer (ICP-OES), optical microscope (OM), scanning electron microscope (SEM) and potentiodynamic polarization measurements. The results show that the absorptivity of La in the HCC TP2 copper tube is about 15% under antivacuum conditions due to the good chemical activities of La. The impurity elements in copper tube such as O, S, Pb and Si can be significantly reduced, and the average columnar dendrite spacing of the copper tube can also be reduced from 2.21 mm to 0.93 mm by adding La. The ultimate tensile strength and the elongation with and without La addition are almost unchanged. However, the annual corrosion rate of the HCC TP2 copper tube is reduced from 10.18 mm•a-1 to 9.37 mm•a-1 by the purification effect of trace La.
      PubDate: 2018-01-01
      DOI: 10.1007/s41230-018-7024-7
      Issue No: Vol. 15, No. 1 (2018)
  • Insulation effect of air cavity in sand mold using 3D printing technology

    • Authors: Cheng-yang Deng; Jin-wu Kang; Hao-long Shangguan; Tao Huang; Xiao-peng Zhang; Yong-yi Hu; Tian-you Huang
      Pages: 37 - 43
      Abstract: The insulation effect of the air cavity surrounding the riser in a 3D printed sand mold was studied. The influence of the air cavity on heat flux was theoretically analyzed. The results demonstrated that the heat flux of the air cavity in the 3D printed sand mold was significantly less than that of resin-bonded sand. The insulation effect of the air cavity in sand molds for a cylinder casting and a stress-frame casting were simulated using software COMSOL. The results illustrated that the air cavity could be used to insulate the riser and it was more suitable for a lower melting point metal casting. An air cavity with 10-15 mm width and 5-10 mm away from the riser can significantly prolong the solidification of the riser by over 10%. Meanwhile, the sand mold for the stress-frame was made by 3D printing technology and poured with aluminum alloy A356 melt. The experiment results showed that the presence of the air cavity led to a 12.5% increase of the solidification time of its riser.
      PubDate: 2018-01-01
      DOI: 10.1007/s41230-018-7243-y
      Issue No: Vol. 15, No. 1 (2018)
  • Phase-field numerical simulation of three-dimensional competitive growth
           of dendrites in a binary alloy

    • Authors: Li Feng; Ya-long Gao; Chang-sheng Zhu; Guo-sheng An; Xin Deng; Bei-bei Jia
      Pages: 44 - 50
      Abstract: The normal vector of migration direction in the solid-liquid interface of dendrites was used to describe the phase-field governing equation. By using the three angles formed by the normal vector for the migration direction of the dendritic growth interface and the coordinate axes of the simulation region, the authors expressed the interfacial anisotropy equation, and built a phase-field model for the competitive growth of multiple grains. Taking a Al-2%mole-Cu binary alloy as an example, the competitive growth of multiple grains during isothermal solidification was simulated by applying parallel computing techniques. In addition, the phase field simulation results were verified by the experimental method. The simulation results show that the competitive growth of equiaxed dendrite is divided into two types: the first occurs during the process of competitive growth, the tips of primary dendrite on different grains taking part in the competition stop growing in their optimal growth direction; the second also occurs during competitive growth, the tips of primary dendrite which participate in the competition on different grains never stop growing in their optimal growth direction. The dendritic morphologies of the first competition growth type are divided into two types. Primary dendrites of grains taking part in the competition stop growing in their optimal growth direction and the competition plane enlarges when neither one wins the competition. However, when one wins the competition, the primary dendrites of grains with superiority go through the blocking grains and continue to grow in their optimal growth direction. The primary dendrites of inferior grains stop growing in their optimal growth direction and then instead grow in those areas without obstacles. The dendritic morphology of the second competition-growth type is shown to be the deformation of primary dendrites, which are mainly represented as the deflection and bending observed from different views. Compared with the metallographic picture, the simulation results can show the morphology of the competitive growth in all directions, so this simulation method can better characterize the competitive growth process.
      PubDate: 2018-01-01
      DOI: 10.1007/s41230-018-7057-y
      Issue No: Vol. 15, No. 1 (2018)
  • Influence of thermal exposure on microstructure and stress rupture
           properties of a new Re-containing single crystal Ni-based superalloy

    • Authors: Chen-guang Liu; Yun-song Zhao; Jian Zhang; Ding-zhong Tang; Chun-zhi Li; Zhen-ye Zhao
      Pages: 51 - 57
      Abstract: In this study, the long-term thermal microstructural stability and related stress rupture lives of a new Re-containing Ni-based single-crystal superalloy, DD11, were investigated after high-temperature exposure for different lengths of time. The results show that the γ′ precipitates retained a cuboidal morphology and the γ′ size increased after short thermal exposure for 50 h at 1,070 °C. As the thermal exposure time was prolonged to 500 h, the cuboidal γ′ gradually changed into irregular raft-like morphology due to particles coalescence, and the morphology of the microstructure was almost unchanged after further thermal exposure up to 3,000 h. The stress rupture experiments at 1,070 °C and a tensile stress of 140 MPa showed that the rupture lives increased significantly after thermal exposure for 50 h and dropped dramatically with increasing exposure time up to 500 h but decreased slowly after exposure for more than 500 h. These results imply that stress rupture properties did not decrease when the γ′ remained cuboidal but degraded to different extents during the γ′ coarsening process. The coarsening of the γ′ precipitates and change in morphology were regarded as the main factors leading to the degradation of the stress rupture lives. This study provides fundamental information on the high-temperature long-term microstructural stability and mechanical performance, which will be of great help for DD11 alloy optimization and engineering aeroengine applications.
      PubDate: 2018-01-01
      DOI: 10.1007/s41230-018-7048-z
      Issue No: Vol. 15, No. 1 (2018)
  • Modeling studies on divorced eutectic formation of high pressure die cast
           magnesium alloy

    • Authors: Meng-wu Wu; Lin Hua; Shou-mei Xiong
      Pages: 58 - 65
      Abstract: The morphology and content of the divorced eutectic in the microstructure of high pressure die casting (HPDC) magnesium alloy have a great influence on the final performance of castings. Based on the previous work concerning simulation of the nucleation and dendritic growth of primary α-Mg during the solidification of magnesium alloy under HPDC process, an extension was made to the formerly established CA (Cellular Automaton) model with the purpose of modeling the nucleation and growth of Mg-Al eutectic. With a temperature field and solute field obtained during simulation of the primary α-Mg dendrites as the initial condition of the modified CA model, modeling of the Mg-Al eutectic with a divorced morphology was achieved. Moreover, the simulated results were in accordance with the experimental ones regarding the distribution and content of the divorced eutectic. Taking a "cover-plate" die casting with AM60 magnesium alloy as an example, the rapid solidification with a high cooling rate at the surface layer of the casting led to a fine and uniform grain size of primary α-Mg, while the divorced eutectic at the grain boundary revealed a more dispersed and granular morphology. Islands of divorced eutectic were observed at the central region of the casting, due to the existence of ESCs (Externally Solidified Crystals) which contributed to a coarse and non-uniform grain size of primary α-Mg. The volume percentage of the eutectic β-Mg17Al12 phase is about 2%-6% in the die casting as a whole. The numerical model established in this study is of great significance to the study of the divorced eutectic in the microstructure of die cast magnesium alloy.
      PubDate: 2018-01-01
      DOI: 10.1007/s41230-018-7207-2
      Issue No: Vol. 15, No. 1 (2018)
  • Effect of reinforcement amount, mold temperature, superheat, and mold
           thickness on fluidity of in-situ Al-Mg 2 Si composites

    • Authors: Reza Vatankhah Barenji
      Pages: 66 - 74
      Abstract: In the present study, the effects of mold temperature, superheat, mold thickness, and Mg2Si amount on the fluidity of the Al-Mg2Si as-cast in-situ composites were investigated using the mathematical models. Composites with different amounts of Mg2Si were fabricated, and the fluidity and microstructure of each were then analyzed. For this purpose, the experiments were designed using a central composite rotatable design, and the relationship between parameters and fluidity were developed using the response surface method. In addition, optical and scanning electron microscopes were used for microstructural observation. The ANOVA shows that the mathematical models can predict the fluidity accurately. The results show that by increasing the mold temperature from 25 °C to 200 °C, superheat from 50 °C to 250 °C, and thickness from 3 mm to 12 mm, the fluidity of the composites decreases, where the mold thickness is more effective than other factors. In addition, the higher amounts of Mg2Si in the range from 15wt.% to 25wt.% lead to the lower fluidity of the composites. For example, when the mold temperature, superheat, and thickness are respectively 100 °C, 150 °C, and 7 mm, the fluidity length is changed in the range of 11.9 cm to 15.3 cm. By increasing the amount of Mg2Si, the morphology of the primary Mg2Si becomes irregular and the size of primary Mg2Si is increased. Moreover, the change of solidification mode from skin to pasty mode is the most noticeable microstructural effect on the fluidity.
      PubDate: 2018-01-01
      DOI: 10.1007/s41230-018-7095-5
      Issue No: Vol. 15, No. 1 (2018)
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