Gating system optimization of low pressure casting A356 aluminum alloy intake manifold based on numerical simulation

To eliminate the shrinkage porosity in low pressure casting of an A356 aluminum alloy intake manifold casting, numerical simulation on fi lling and solidifi cation processes of the casting was carried out using the ProCAST software. The gating system of the casting is optimized according to the simulation results. Results show that when the gating system consists of only one sprue, the fi lling of the molten metal is not stable; and the casting does not follow the sequence solidifi cation, and many shrinkage porosities are observed through the casting. After the gating system is improved by adding one runner and two in-gates, the fi lling time is prolonged from 4.0 s to 4.5 s, the fi lling of molten metal becomes stable, but this casting does not follow the sequence solidifi cation either. Some shrinkage porosity is also observed in the hot spots of the casting. When the gating system was further improved by adding risers and chill to the hot spots of the casting, the shrinkage porosity defects were eliminated completely. Finally, by using the optimized gating system the A356 aluminum alloy intake manifold casting with integrated shape and smooth surface as well as dense microstructure was successfully produced.

Numerical simulation and experimental study of hybrid laser-electric arc welding between dissimilar Mg alloys

This work aims to establish a suitable numerical simulation model for hybrid laser-electric arc heat source welding of dissimilar Mg alloys between AZ31 and AZ80. Based on the energy conservation law and Fourier’s law of heat conduction, the differential equations of the three-dimensional temperature field for nonlinear transient heat conduction are built. According to the analysis of nonlinear transient heat transfer, the equations representing initial conditions and boundary conditions are obtained. The “double ellipsoidal heat source + 3D Gaussian heat source”combination was chosen to construct the laser-electric arc hybrid heat source. The weld bead morphologies and the distribution of temperature, stress, displacement and plastic strains are numerically simulated. The actual welding experiments were performed by a hybrid laser-electric arc welding machine. The interaction mechanism between laser and electric arc in the hybrid welding of Mg alloys is discussed in detail. The hybrid heat source can promote the absorption of laser energy and electric arc in the molten pool, resulting in more uniform energy distribution in the molten pool and the corresponding improvement of welding parameters. This work can provide theoretical guidance and data supports for the optimization of the hybrid laser-electric arc welding processes for Mg alloys.

Microstructures of an AlSi_7Mg alloy by near-liquidus casting

Semi-solid ingots of an A1SiTMg alloy were obtained using the method of near liquidus casting. Their microstructures exhibit the characteristics of free, equiaxed, and non-dendrite, which are required for semi-solid forming. The influences of casting temperature, heat preservation time, and cooling rate on the microstructure were also investigated. The results show that in the temperature region near liquidus the grain size becomes small with a decrease in casting temperature. Prolonging the heat preservation time makes grain crassitude at the same temperature. And increasing the cooling rate makes grain fine. The microstructure of the alloy cast with iron mould is freer than that with graphite mould.

Shear behavior of AZ80 Mg alloy using experimental, theoretical and numerical techniques

The shear punch test(SPT)is a suitable experiment for characterizing the shear behavior of various materials,especially where there are volume limitations.In the present investigation,the relations among various parameters such as clearance,die diameter and sample thickness,and the yield and ultimate shear strengths of AZ80Mg alloy were studied.Moreover,based on the Mohr-Coulomb theory,relatively optimum conditions were introduced for the shear punch test.With this regard,a range of2%-10%is found to be suitable for the clearance/sheet thickness ratio.To provide a simple shear stress state during a shear punch test,it is also necessary to select the die diameter/sheet thickness ratio between2:1and10:1.Based on the predictions of the Mohr-Coulomb theory,it is better to conduct a room-temperature shear punch test with a sample thickness of0.5mm,a clearance of25μm and a die diameter of2mm.Finally,the mean conversion factors to gain the tensile and compressive yield strengths of the cast AZ80from its shear one are found to be1.70and3.09,respectively.

Influence of pouring methods on filling process,microstructure and mechanical properties of AZ91 Mg alloy pipe by horizontal centrifugal casting

Pouring position as the input heat source has great infl uence on the temperature fi eld evolution. In this study, the Flow3 D simulation software was applied to investigate the infl uence of pouring methods(with fi xed 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 signifi cantly decreased. Meanwhile, serious macro-segregation appeared in the AZ91 casting pipe by the fi xed pouring channel HCC process. Compared with the fi xed 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.

Numerical simulation on the rheo-diecasting of the semi-solid A356 aluminum alloy

The effect of injection pressure, piston velocity, and the forming temperature of semisolid slurry on the filling behavior of the semi-solid A356 aluminum alloy was investigated by simulation methods. The simulation results show that these processing parameters have an important effect on the filling behavior of the semi-solid A356 aluminum alloy. The slurry flows steadily in the cavity when the injection pressure, the piston velocity, and the forming temperature are low, but it is prone to turbulent flow when the injection pressure, the piston velocity, and the forming temperature are much higher. Therefore it is necessary to determine the appropriate processing parameters to get a steady flow of the slurry in the cavity.

Numerical simulation for macrosegregation in direct-chill casting of 2024 aluminum alloy with an extended continuum mixture model

An extended continuum mixture model for macrosegregation is applied to predicting Cu and Mg segregation in large-size ingot of 2024 aluminum alloy during direct chill casting（DC）. A microsegregation model using the approximate phase diagram data was coupled with macroscopic transport equations for macrosegregation profiles. Then, the impacts of transport mechanisms on the formation of macrosegregation were discussed. It is found that copper and magnesium have a similar segregation configuration from the billet center to surface. Negative segregation is observed in the centerline and subsurface, whereas positive segregation is obtained in the surface and somewhat underestimated positive segregation in the middle radius. Further, the discrepancy between the predicted and experimental results was discussed in detail. The results show that the magnesium to some extent alleviates the copper segregation in ternary alloy, compared with that in binary alloy. The predicted results show good agreement with measured experimental data obtained from literatures.

Numerical Simulation of Microporosity Evolution of Aluminum Alloy Castings

A mathematical model to calculate the size and distribution of microporosities was studied and coupled with a stochastic microstructure evolution model. The model incorporates various solidification phenomena such as grain structure evolution, solidification shrinkage, interdendritic fluid flow and formation and growth of pores during solidification processes. The nucleation and growth of grains were modeled with a cellular automaton method that utilizes the results from a macro scale modeling of the solidification process. Experiments were made to validate the proposed models. The calculated results of aluminum alloy castings agreed with the experimental measurements.

Numerical Simulation of Bubble Migration in Liquid Titanium Alloy Melt During Vertical Centrifugal Casting Process

The bubble migration in liquid titanium alloy melt during vertical centrifugal casting process has been predicted. The effects of different parameters, such as the initial bubble location, the mold rotational speed and the mold rotational direction on the bubble in the migration process are investigated. The results show that the bubble migration can be divided into the radial movement to the mould rotation axis and the circular movement to the mould wall opposite to rotational direction of the casting mould. The casting mould wall has an impeditive effect on the circular movement of the bubble during its migration process. And the bubble finally migrates like a straight line along the mould wall located at the opposite direction of the rotational casting mould whether it rotates clockwise or anti-clockwise. The bubbles at the position near the mould wall located at the opposite direction of the rotational casting mould are much easier to migrate in a straight line. The instantaneous speed of the gas bubble increases with the increment of the mould rotational speed. However the mould rotational speed is high or low, the moving speed of the gas bubble increases slightly at the primary stage, and then decreases gradually like a ladder.

Numerical simulation for mold-filling of thin-walled aluminum alloy castings in traveling magnetic field

The numerical simulation for mold-filling of thin-walled aluminum alloy castings in horizontal traveling magnetic field is performed. A force model of Al alloy melt in the traveling magnetic field is founded by analyzing traveling magnetic field carefully. Numerical model of Al alloy mold-filling is founded based on N-S equation, which was suitable for traveling magnetic field. By using acryl glass mold with indium as alloy melt, the experiment testified the filling state of alloy in traveling magnetic field. The results of numerical simulation indicate that the mold-filling ability of gallium melt increases continually with the increase of the input ampere turns.

Numerical simulation of continuous roll-casting process of aluminum alloy

In order to improve the strip quality of continuous roll-casting process (CRP) of aluminum alloy, the investigations of the flow behavior within the metal pool, the heat transfer condition between roll and strip, the pouring temperature of molten alloy, the roll-casting speed and the control of the position of solidification final point are important. The finite volume method was applied to the analysis of the continuous roll-casting process. A two-dimensional incompressible non-Newtonian fluid flow with heat transfer was considered, which was described by the continuity equation, the Navier-Stokes equation and the energy equation. With this mathematical model, the flow patterns, temperature fields and solid fraction distributions in the metal pool between two rolls were simulated. From the calculated results, the effects of technical parameters to the position of solidification final point are obtained. The simulated results show that the roll-casting speed and pouring temperature have an enormous effect on the temperature distribution and the position of solidification final point.

Numerical simulation and experimental investigation of two filling methods in vertical centrifugal casting

A mathematical model of the centrifugal filling process was established. The calculated results show that the centrifugal field has an important influence on the filling process. Moreover, the process of liquid flow and the location of free surface in sprue were simulated based on the Solution Algorithm-Volume of Fraction (SOLA-VOF) technique. In order to verify the mathematical model and computational results, hydraulic simulation experiment was carried out. The results of experiments and numerical simulation indicate the accuracy of mathematical model. Two kinds of filling methods were investigated and the results show that the bottom filling is better than the top filling that can achieve stable filling and reduce defects.

Numerical simulation on reho-diecasting mould filling of an automobile master brake cylinder

An apparent viscosity model of semi-solid A356 aluminum alloy has been developed and the software Castsofl6.0 coupled with the model has been used to simulate the mould filling of an automobile master brake cylinder with the semi-solid A356 aluminum alloy slurry. The simulation results are in agreement with the practical filling process, indicating that the apparent viscosity model is feasible and can be used to simulate the mould filling of the semisolid A356 aluminum alloy slurry and can be used to optimize the filling process and the design of dies. A higher injection pressure, a higher ingate flow velocity of the semi-solid slurry, and a higher slurry temperature are advantageous to the mould filling of the automobile master brake cylinder.

Effect of pouring temperature on cooling slope casting of semi-solid Al-Si-Mg alloy

Present trend of semi-solid processing is directed towards rheocasting route which allows manufacturing of near-net-shape cast components directly from the prepared semi-solid slurry. Generation of globular equi-axed grains during solidification of rheocast components, compared to the columnar dendritic structure of conventional casting routes, facilitates the manufacturing of components with improved mechanical properties and structural integrity. In the present investigation, a cooling slope has been designed and indigenously fabricated to produce semi solid slurry of A1-Si-Mg （A356） alloy and successively cast in a metallic mould. The scope of the present work discusses about development of a numerical model to simulate the liquid metal flow through cooling slope using Eulerian two-phase flow approach and to investigate the effect of pouring temperature on cooling slope semi-solid slurry generation process. The two phases considered in the present model are liquid metal and air. Solid fraction evolution of the solidifying melt is tracked at different locations of the cooling slope, following Schiel＇s equation. The continuity equation, momentum equation and energy equation are solved considering thin wall boundary condition approach. During solidification of the liquid metal, a modified temperature recovery scheme has been employed taking care of the latent heat release and change of fraction of liquid. The results obtained from simulations are compared with experimental findings and good agreement has been found.

Numerical simulation and experiment validation of thixoforming angle frame of AZ61 magnesium alloy

Numerical simulation and experiment of thixoforming angle frame of AZ61 magnesium alloy were investigated.The results show that with the increase in punch displacement,cylinder billet firstly fills into die cavity of angle frame from feed inlet and plastic deformation occurs in touching region between billet and die cavity.After central thin wall of angle frame is created,semi-solid billet fills toward two edges.Lastly,complete plastic deformation occurs in billet,leading to complete filling of semis-olid billet.Effective strain,effective stress and billet temperature decrease with the increase in punch displacement.Effective stress decreases with the increase in billet temperature,die temperature and punch velocity.The optimal conditions decided by numerical simulation are as follows:die temperature of 450 ℃,billet temperature of 560 ℃ and punch velocity of 30 mm/s.Angle frame components with high mechanical properties such as yield strength of 225 MPa,tensile strength of 309 MPa and elongation of 21.8% and fine microstructure could be thixoformed successfully according to process parameters decided by numerical simulation.

Thermal-stress Simulation of Direct-chill Casting of AZ31 Magnesium Alloy Billets

Two-dimensional （2D） transient coupled finite element model was developed to compute the temperature and stress field in cast billets, so as to predict the defects of the I-type billets made from AZ31 magnesium alloy and find the causes and solutions for surface cracks and shrinkages during direct-chill （DC） casting process. Method of equivalent specific heat was used in the heat conduction equation. The boundary and initial conditions used for primary and secondary cooling were elucidated on the basis of the heat transfer during the solidification of the billet. The temperature and the thermal-stress fields were simulated with the thermal-structural coupled module of ANSYS software. The influences of casting parameters on the distributions of temperature and stress were studied, which helped optimize the parameters （at pouring temperature of 680 ℃, casting speed of 2 min/s, heat-transfer coefficient of the second cooling equals to 5 000 W/m^2.℃^-1）. The simulation results of thermal stress and strain fields reveal the formation mechanism of some casting defects, which is favourable for optimizing the casting parameters and obtain high quality billets. Some measures of controlling processes were taken to prevent the defects for direct-chill casting billets.

Hot cracking tendency test and simulation of 7075 semi-solid aluminium alloy

The hot cracking tendency of 7075 semi-solid alloy under different conditions was studied by critical diameter method.The experiment and simulation results show that the dendrite arms of the rod grow from the edge to the center.The smaller the diameter of the rod is,the more obvious the directional growth of dendrite is,and the greater the tendency of hot cracking is.Compared with ordinary melt,for semi-solid slurry,increasing mould temperature or decreasing pouring temperature can significantly decrease hot cracking tendency of 7075 alloy,decreasing hot cracking grade from 256 to 100 mm^2.Furthermore,based on the RDG criterion,the effects of solidification conditions on the hot cracking tendency were discussed combined with simulation.At the same time,the application and development of RDG criterion were also researched.

Effects of process parameters on semi-solid squeeze casting performance of aluminum alloy scrolls for scroll compressors

The aluminum alloy scroll is one of the key parts of the scroll compressors widely used in the air-conditioning,refrigeration,and heat pump systems.In this work,the semi-solid squeeze casting(SSSC)process was used to fabricate the aluminum alloy scroll.The effects of process parameters including the pouring temperature,mold temperature,and squeezing velocity on the filling and solidification behaviors of the alloys were investigated through simulations based on the power law cut-off(PLCO)material model.Results show that there is a significant increase in the flow velocity of the slurry,and the area of the high-speed region enlarges with the increase of the pouring temperature.The homogeneity of the temperature and velocity fields in the slurry is improved with an increase in mold temperature.Both the filling time and its variation rate decrease with an increase in squeezing velocity.The maximum solidification time exhibits a linear variation with the increase in pouring temperature.The shrinkage area is decreased by increasing the mold temperature.The optimal process parameters of the SSSC process were obtained from simulation analysis,which are the pouring temperature of 595°C,mold temperature of 350°C,and squeezing velocity of 0.3 m·s-1.Moreover,the qualified scroll casting was fabricated using the SSSC process under the optimal process parameters.

Macro-physical field of large diameter magnesium alloy billet electromagnetic direct-chill casting:A comparative study

A comprehensive two-dimensional axisymmetric mathematical model that couples transient electromagnetic force with fluid flow,heat transfer,and solidification was established to describe the interaction of multiphysics field during DC casting.The melt flow,heat transfer,and solidification characteristics under differential phase pulse magnetic field and differential phase low-frequency electromagnetic field(DP-PMF and DP-LFEF)were numerically investigated by means of numerical simulation during electromagnetic direct-chill(DC)casting of AZ31 alloy at the same casting conditions.The effects of differential phase electromagnetic fields on Lorentz forces distributions,melt flow,heat transfer,and liquid sump shape were discussed systematically.Based on measured current waveform,the results were compared with those obtained without magnetic field(MF)and under conventional pulse magnetic field(PMF)and low-frequency electromagnetic field(LFEF)under the same conditions.The results show that the application of magnetic fields can significantly change the solidification process of DC casting.Differential phase magnetic fields(DP-LFEF and DP-PMF)can effectively reduce the temperature of the melt in the liquid sump,and the shallower liquid sump depth can be obtained under the differential phase magnetic fields.A large velocity vibration amplitude and a lower temperature are available simultaneously under DP-PMF,resulting in more uniform temperature distribution.

Inhomogeneity of density and mechanical properties of A357 aluminum alloy backward extruded in semi-solid state

The inhomogeneity of density and mechanical properties of A357 aluminum alloy in the semi-solid state were investigated.Numerical simulation and backward extrusion were adopted to study the preparation of cup shells.The results show that the relative density of the wall is the lowest in samples,and that of the base is the highest.With increasing the billet height,more time is needed for relative density of the corner to reach the maximum value,and the relative densities in every region improve evidently with increasing the pressure.The tensile stress was simulated to be the largest at the corner,and the hot tearings were forecasted to mainly appear at the corner too.By employing proper billet height and pressure,the extruded samples consisted of fine and uniform microstructures,and can obtain excellent mechanical properties and Brinell hardness.