Modeling and simulation of 3D thermal stresses of large-sized castings in solidification processes

When heavy machines and large scaled receiver system of communication equipment are manufactured, it always needs to produce large-sized steel castings, aluminum castings and etc. Some defects of hot cracking by thermal stress often appear during solidification process as these castings are produced, which results in failure of castings. Therefore predicting the effects of technological parameters for production of castings on the thermal stress during solidification process becomes an important means. In this paper, the mathematical models have been established and numerical calculation of temperature fields by using finite difference method (FDM) and then thermal stress fields by using finite element method (FEM) during solidification process of castings have been carried out. The technological parameters of production have been optimized by the results of calculation and the defects of hot cracking have been eliminated. Modeling and simulation of 3D thermal stress during solidification processes of large-sized castings provided a scientific basis, which promoted further development of advanced manufacturing technique.

Effect of Yttrium on the Solidification Process and Performance of Al7SiMg Alloy

Solidification processes of Al7SiMg-xY(0.1wt%,0.3wt%,0.5wt%) alloys were investigated by thermal analysis.The microstructures were observed by using optical microscopy and scanning electron microscopy.Effects of different concentrations of yttrium on tensile performance both as cast and T6 heat treated were studied at room temperature,respectively.The results show that little changes happen in liquidus with increases concentration of yttrium.While it results in obvious depression of solidus and eutectic arrest temperature in solidification process.Moreover,the solidification range increases significantly.The performance is better when concentration of yttrium is 0.1wt%.With increment of yttrium,more large flake-like compounds of yttrium gather in grain boundaries,performance especially the elongation of the alloy decrease remarkably.

Calculation of Solidification Process of Continuous Cast Bar

In this paper,it presents the results of calculation of solidification process of copper continuous cast bar by cross section size 120 mm × 70 mm with application of Pro Cast 2010 software. The estimation of mould design effect on solidification process of continuos copper cast bar is completed at various speeds of casting.Profiles of liquid metal cavities and temperature allocations in the cast bar at various casting speeds are defined.The analysis of received liquid metal cavity profiles shows that a new mold construction allows significantly decrease of the length of the liquid metal cavity during continuous copper casting at HAZELETTcasting machine and the increase of maximum casting speed from 10 to 11 m / min. Adequacy of the results of copper continuous cast bar solidification process calculation is confirmed by the experimental data.

Numerical prediction of the incremental melting and solidification process

A mathematical formulation is applied to represent the phenomena in theincremental melting and solidification process (IMSP), and the temperature and electromagneticfields and the depth of steel liquid phase are calculated by a finite difference technique using thecontrol volume method. The result shows that the predicted values are in good agreement with theobservations. In accordance with the calculated values for different kinds of materials anddifferent size of molds, the technological parameter of the IMS process such as the power supply andthe descending speed rate can be determined.

3-D Finite-Element Numerical Simulation of Centrifugal Induction Electrosalg Casting Solidification Process

A 3-D finite-element numerical simulation model of temperature field for CIESC casting solidification process was developed with the aid of ANSYS software and a series of corresponding experiments were made. The results showed that the good agreement was obtained between the numerical simulation and the experiments. Based on the numerical simulation results, the characteristics of temperature distribution in the castings during CIESC solidification process were analyzed and summarized. According to the G/R-1/2 method and numerical simulation results, there is no any shrinkage defect in the CIESC casting and structure or casting is fine and compact.

Recent research progress on the phase-field model of microstructural evolution during metal solidification

Solidification structure is a key aspect for understanding the mechanical performance of metal alloys,wherein composition and casting parameters considerably influence solidification and determine the unique microstructure of the alloys.By following the principle of free energy minimization,the phase-field method eliminates the need for tracking the solid/liquid phase interface and has greatly accelerated the research and development efforts geared toward optimizing metal solidification microstructures.The recent progress in the application of phasefield simulation to investigate the effect of alloy composition and casting process parameters on the solidification structure of metals is summarized in this review.The effects of several typical elements and process parameters,including carbon,boron,silicon,cooling rate,pulling speed,scanning speed,anisotropy,and gravity,on the solidification structure are discussed.The present work also addresses the future prospects of phase-field simulation and aims to facilitate the widespread applications of phase-field approaches in the simulation of microstructures during solidification.

Effects of mechanical vibration on filling and solidification behavior, microstructure and performance of Al/Mg bimetal by lost foam compound casting

Al/Mg bimetal was prepared by lost foam solid-liquid compound casting,and the effects of mechanical vibration on the filling and solidification behavior,microstructure and performance of the bimetal were investigated.Results show that the mechanical vibration has a remarkable influence on the filling and solidification processes.It is found that after mechanical vibration,the filling rate increases and the filling rate at different times is more uniform than that without vibration.In addition,the mechanical vibration also increases the wettability between liquid AZ91D and A356 inlays.The mechanical vibration reduces the horizontal and vertical temperature gradient of the casting and makes the temperature distribution of the whole casting more uniform.Compared to the Al/Mg bimetal without vibration,the shear strength is improved by 39.76%after the mechanical vibration is applied,due to the decrease of the inclusions and Al_(12)Mg_(17) dendrites,and the refinement and uniform distribution of the Mg_(2)Si particles in the interface of the Al/Mg bimetal.

δ/δ Grain Boundary Movement in Fe-0.2%C-0.8%Cr During Solidification Process

The moving process ofδ / δgrain boundary during the solidification process of Fe-0.2%C-0.8%Cr has been observed in-situ with confocal scanning laser microscope （ CSLM ）, and the establishment of δ/δ grain boundary , the moving mode , the moving speed and the influence of correlative factor were explored in detail.The results showed that the clear grain cannot be formed when δ phase merged during solidification process of the steel if the actual cooling rate was 0.045℃·s-1 .The δ/δgrain boundary with shape of flat will be formed if there is no essential conjunction betweenδphase in a long period of time.The movement ofδgrain boundary cross point drives other δ /δ grain boundaries to move.The moving process is not stable , and the moving rate variation ranges from 0.12to 1.65 μ m ·s-1 .Temperature of the system is the chief factor for influencing the moving rate of δ / δgrain boundary during the solidification.When the temperature fluctuation of system appears , the solidified grain boundary is re-melted , which results in the catastrophic fluctuation of moving rate for δ / δ grain boundary.When the solidification process reaches its end , the average moving rate of δ /δ grain boundary is quicker than that of L / δ interface.The coarsening rate of crystal grain in the melt is slower than that of solidified solid phase crystal grain.

Progress of Solidification Researches and the Applications in Materials Processing

The research achievements of solidification theories and technologies in the last decades are reviewed with the stresses on some new development in the recent years. Some new interesting areas emerged in the last years are also pointed out.

MY CONTRIBUTIONS TO THE PHYSICAL PROCESS OF SOLIDIFICATION

In 1950, I graduated from Tsinghua University,majoring in machine building. Three years later, Ientered the Iron & Steel College in Moscow to start studying metallurgy as a postgraduate. After obtaining my associate professorship, I came back home. I devoted the succeeding 40 years to the theory and technology of solidification, because I had realized the importance of the physical process of solidification in materials science and engineering technologies as a means of upgrading the properties of traditional materials and developing new materials. My contributions in this field might be listed as follows:

Direct Generation of Intense Compression Waves in Molten Metals by Using a High Static Magnetic Field and Their Application

Compression waves propagating through molten metals are contributed to degassing, accelerating reaction rate,removing exclusions from molten metals and refining solidification structures during metallurgical processing of materials. In the present study, two electromagnetic methods are proposed to generate intense compression wavesdirectly in liquid metals. One is the simultaneous imposition of a high frequency electrical current field and a staticmagnetic field; the other is that of a high frequency magnetic field and a static magnetic field. A mathematical modelbased on compressible fluid dynamics and electromagnetic fields theory has been developed to derive pressure distributions of the generated waves in a metal. It shows that the intensity of compression waves is proportional to thatof the high frequency electromagnetic force. And the frequency is the same as that of the imposed electromagneticforce. On the basis of theoretical analyses, pressure change in liquid gallium was examined by a pressure transducerunder various conditions. The observed results approximately agreed with the predictions derived from the theoreticalanalyses and calculations. Moreover, the effect of the generated waves on improvement of solidification structureswas also examined. It shows that the generated compression waves can refine solidification structures when they wereapplied to solidification process of Sn-Pb alloy. This study indicates a new method to generate compression wavesby imposing high frequency electromagnetic force locally on molten metals and this kind of compression waves canprobably overcome the difficulties when waves are excited by mechanical vibration in high temperature environments.

FINITE ELEMENT NUMERICAL SIMULATION OF TEMPERATURE FIELD IN METAL PATTERN CASTING SYSTEM AND "REVERSE METHOD" OF DEFINING THE THERMAL PHYSICAL COEFFICIENT

With the technology support of virtual reality and ANSYS software, an example on the simulation of temperature distribution of casting system during the solidification process was provided, which took the latent heat of phase change, the conditions for convection, and the interface heat transfer coefficient into consideration. The result of ANSYS was found to agree well with the test data. This research offers an unorthodox way or ＂reverse method＂ of defining the relevant thermal physical coefficient.

Behavior of Inclusions in Process of Solid Growth During Solidification of Fe-0.15C-0.8Mn Steel

The behavior of inclusions in the process of B-phase growth during the solidification of Fe-0.15C-0.8Mn steel was in-situ observed using a high-temperature confocal scanning laser microscope （HTCSLM）. The results show that inclusions arrive the S/L （solid/liquid） interface by way of direct impact or gradual drift, when the ceil spacing is approximately equal to 177 um during the growth of cellular B-phase. The inclusions easily stay at the positions of trailing vortex formed by the circumferential motion of molten steel around B-phase. Some inclusions reaching the S/L interface are captured by the solid-phase. Some of them move along the normal direction of the S/L in- terface because of pushing of solid-phase, and the others get away from the S/L interface after being pushed for a distance. The faster the growth rates of the solid-phase are, the easier the inclusions are captured by the S/L interface. The slower the growth rates of the solid-phase are, the easier the inclusions move with the S/L interface.

Design and application of a multichannel"cross"hot tearing tendency device:A study on hot tearing tendency of Al alloys

Hot tearing is one of the most serious defects during the casting solidification process.In this study,a new type of multichannel"cross"hot tearing device was designed.The hot cracks initiation and propagation were predicted by the relationship between temperature,shrinkage force and solidification time during the casting solidification process.The reliability and practicability of the multichannel"cross"hot tearing device were verified by casting experiments and numerical simulations.The theoretical calculation based on Clyne-Davies model and numerical simulation results show that the hot tearing tendency decreases in the order:2024 Al alloy>Al-Cu alloy>Al-Si alloy at a pouring temperature of 670°C and a mold temperature of 25°C.Feeding of liquid films at the end of solidification plays an important role in the propagation process of hot tearing.The decrease of hot tearing tendency is attributed to the feeding of liquid film and intergranular bridging.

In-situ composite Cu-Cr contact cables with high strength and high conductivity

In order to develop a new type of contact cable with high strengthand high electrical conductivity, Cu-Cr alloy series were selected asmaterials and cu-Cr alloy castings were produced by means ofdirectional solidification continu- ous casting (DSCC) process. theresults show that the fibrillar strengthening phase, β-Cr, orderlyarranges among the copper matrix phase along the wire direction; andmicrostructure of in-situ composite forms, which retains the basicproperty of good conductivity of the copper matrix and meanwhileobtains the strengthening effect ofβ-Cr phase.

Grain Size Distribution and Interfacial Heat Transfer Coefficient during Solidification of Magnesium Alloys Using High Pressure Die Casting Process

The objective of this study is to predict grain size and heat transfer coefficient at the metal-die interface during high pressure die casting process and solidification of the magnesium alloy AM60. Multiple runs of the commercial casting simulation package, ProCASTTM, were used to model the mold filling and solidification events employing a range of interfacial heat transfer coefficient values. The simulation results were used to estimate the centerline cooling curve at various locations through the casting. The centerline cooling curves, together with the die temperature and the thermodynamic properties of the alloy, were then used as inputs to compute the solution to the Stefan problem of a moving phase boundary, thereby providing the through-thickness cooling curves at each chosen location of the casting, Finally, the local cooling rate was used to calculate the resulting grain size via previously established relationships. The effects of die temperature, filling time and heat transfer coefficient on the grain structure in skin region and core region were quantitatively characterized. It was observed that the grain size of skin region strongly depends on above three factors whereas the grain size of core region shows dependence on the interracial heat transfer coefficient and thickness of the samples. The grain size distribution from surface to center was estimated from the relationship between grain size and the predicted cooling rate. The prediction of grain size matches well with experimental results. A comparison of the predicted and experimentally determined grain size profiles enables the determination of the apparent interracial heat transfer coefficient for different locations.

Increasing Solidification Rate of M2 High-Speed Steel Ingot by Fusible Metal Mold

As one of the most popular used high-speed steels, M2 possesses excellent hardness and toughness as cutting tools. Networks of eutectic carbides distributing in the inter-dendritic region are academically considered to be the typical microstructure of M2, which can be refined by increasing cooling rate. In this paper, a novel casting method named fusible metal mold （FMM） is employed to refine the microstructure of M2 high-speed steel. Results show that FMM casting method can improve cooling rate by 100% without any contamination of the melts＇ composition.

Melting/solidification of phase change material in a multi-tube heat exchanger in the presence of metal foam:effect of the geometrical configuration of tubes

One of the likely methods for enhancing heat transfer in a latent thermal energy storage system is the conception of a thermal unit.In this study,the orientation of oval tubes(horizontal,vertical,and oblique)in phase change material(PCM,C_(19)-C_(20))-based shell-tube heat exchanger was analyzed with respect to the metal foam(MF)type(graphite,copper,and nickel)in comparison to the case of pure PCM.For this purpose,a two-dimensional mathematical model was developed to investigate the thermal efficiency of the PCM-metal foam based composite energy storage unit.It was concluded that the orientation of the oval tubes(oblique,horizontal,and vertical)has a negligible impact on the performance of the thermal unit during the melting/solidification processes.Based on the liquid/solid fraction,total enthalpy and the average temperature in the annular space,the performance of a heat exchanger during fusion/solidification periods is in the order:copper-MF>graphite-MF>nickel-MF>pure PCM.Whatever the adopted MF or the geometry of tubes,the melting process is expedited compared to the solidification mechanism.

Lateral Growth Rate of Cells in Melt

Growth process of δ-phase was studied during the solidification of carbon steel.Through analyzing the solute diffusion around cylindrical crystals in the melt,the mathematic representation of lateral growth rate of cylindrical crystals was confirmed;the calculation and analysis of lateral growth rate were carried out.In order to validate the theoretical calculation and analysis,the growth process of δ-phase during the solidification was in-situ observed using a confocal scaning laser microscope（CSLM） and the growth rates were measured through CSLM images.The results show that lateral growth rates of δ-phase in the carbon steel first rapidly decrease with the increase of the radius of the cylindrical crystal,and then slowly fall down or maintain invariable.The radius of δ-phase is the primary factor to affect the growth rate.The higher the temperature gradient is,the bigger the growth rate is.However,the effect of the temperature gradient is feeble.Good correlation is obtained between theoretical analysis and experiment results in absolute values of lateral growth rate and change rule