Microstructure and mechanical properties of Mg-Gd-Y-Zr alloy cast by metal mould and lost foam casting

The microstructure and mechanical properties of Mg-10.1Gd-3.74Y-0.25Zr （mass fraction, %） alloy （GW104 alloy） cast by metal mould casting （MMC） and lost foam casting （LFC） were evaluated, respectively. It is revealed that different forming modes do not influence the phase composition of as-cast alloy. In the as-cast specimens, the microstructures are similar and composed of α-Mg solid solution, eutectic compound of α-Mg＋Mg 24 （Gd, Y） 5 and cuboid-shaped Mg 5 （Gd, Y） phase; whereas the average grain size of the alloy produced by metal mould casting is smaller than that by lost foam casting. The eutectic compound of the alloy is completely dissolved after solution treatment at 525 ℃for 6 h, while the Mg 5 （Gd, Y） phase still exists after solution treatment. After peak-ageing, the lost foam cast alloy exhibits the maximum ultimate tensile strength of 285 MPa, and metal mould cast specimen 325 MPa at room temperature, while the tensile yield strengths of them are comparable. It can be concluded that GW104 alloy cast by lost foam casting possesses similar microstructure and evidently lower mechanical strength compared with metal mould cast alloy, due to slow solidification rate and proneness to form shrinkage porosities during lost foam casting process.

Performance of digital patternless freeze-casting sand mould

Digital patternless freeze-casting technology is a new approach for obtaining frozen sand moulds using digital milling technology. The change law of tensile strength and air permeability of frozen sand moulds (100-mesh and 200-mesh silica sand, and zircon sand moulds) under different freezing temperatures and water contents was studied. Results show that with the decrease of freezing temperature and the increase of water contents, the tensile strength and air permeability of the sand moulds are gradually improved. Meanwhile, computed tomography technology was used to characterize the shape and size of the water film between the sand particles mixed with 4wt.% water. The results show that in silica sand moulds, the form of water film is lumpy, and 200-mesh silica sand moulds have more water films and higher proportion of small-sized water films than 100-mesh silica sand moulds, while in zircon sand moulds, the form of water film is membranous. At the same freezing temperature and water content, the tensile strength of zircon sand mould is the highest, and 100-mesh silica sand mould is the lowest. A comparative solidification experiment of A356 aluminum alloy was carried out in frozen sand mould and resin sand mould. The results show that the primary α-Al phase appears in the form of equiaxed and eutectic silicon phase is needle-like in freezing sand mould casting, but the primary α-Al phase grows in the form of dendrites, and the eutectic silicon phase is coarse needle-like in the resin sand mould casting. The difference of microstructure is caused by the different cooling rate. The cooling rate of A356 aluminum alloy in frozen sand mould is higher than that in resin sand mould.

Theoretical and experimental analysis of continuous casting with soft-contacted mould

Coupling the quasi 3D numerical simulation of electromagnetic field and the experiments with some metals such as tin, aluminum, copper and steel, the electromagnetic characteristics of continuous casting with soft contacted mould, especially the influences of power frequency, the mould structure, and the inductor position, size and current on the electromagnetic force and pressure on the billet, were analyzed. The result shows that, in continuous casting with soft contacted mould, the electromagnetic pressure on the surface of billet increases with the rising of the power frequency as a logarithmically parabolic function and, with that of inductor current as a parabolic function. The design principle of the soft contacted mould is that 1) the mould structure should be ‘more segments and thin slits’; 2) the topside of inductor should be at the same location with the meniscus of molten metal; 3) the inductor should cover the initial solidifying shell of billet.

Improvement in collapsibility of ZrO2 ceramic mould for investment casting of TiAl alloys

Investment casting has been widely recognized as the best option in producing TiAl components with key benefits of accuracy,versatility and integrity.The collapsibility of ceramic moulds for investment casting is critical in the manufacturing process of TiAl components due to TiAl's intrinsic brittleness at room temperature.The aim of the present research is to provide a method for production of TiAl components by investment casting in ZrO2 ceramic moulds with improved collapsibility.Slurries prepared with high polymer additions were utilized during the preparation of ceramic moulds.The stress/strain curves obtained from green and baked ceramic moulds demonstrate that the green strength was increased with the application of high polymer,while baked strength decreased,thus the collapsibility of ceramic moulds was improved.It is suggested that this result is related to the burn-out of high polymer which left a lot of cavities.The experimental findings were also verified by the investment casting of "I"-shaped TiAl components.

THE COMPUTATION AND EXPERIMENT ANALYSIS OF ELECTROMAGNETIC CONTINUOUS CASTING WITH SOFT-CONTACTED MOULD

In this paper, coupling the quasi-3D numerical simulation of electromagnetic field and the experiments of continuous casting with soft-contacted mould with some metals such as tin, aluminum, copper and steel, the electromagnetic characteristics of continuous casting with soft-contacted mould is analyzed. It is shown that the electromagnetic pressure on the surface of billet is increasing with the rising of power frequency as a logarithmically parabolic function, with that of electric conductivity of billet as a power junction, and with that of the current in inductor as a parabolic junction.

MATHEMATICAL AND PHYSICAL MODELING OF INTERFACIALPHENOMENA IN CONTINOUS CASTING MOULD WITH ARGONINJECTION THROUGH SUBMERGED ENTRV NOZZLE

The study on the fluid flow, meniscus oscillation, slag entrapment in continuous casting mould was conducted mathematically and experimentally. The results show that the injection of argon into submerged nozzle enhances the meniscus oscillation, thus increases the probability of slag entrapment, and the critical argon blowing flow rate, which will give rise to slag entrapment, is around 10l/min. The trajectory of bubble is affected by the bubble diameter and the molten steel flow, and the bubble diameter is dominant. The bubble with diameter 1.4mm floats fastest with 0.47m/s terminal velocity.

Numerical simulation and optimization of shell mould casting process for leaf spring bracket

Although the shell mould casting process has a wide range of application in many fields,the prediction of casting defects is still a problem.In the present work,a typical leaf spring bracket casting of ZG310-570 was fabricated by shell mold casting.The finite element model and ProCAST software were utilized for simulating the filling and solidification processes of the casting;and the formation mechanism of the gas pore,and shrinkage porosity defects were analyzed.The results indicate that the gas pore and shrinkage porosity defects are formed due to air entrapment,insufficient feeding and non-sequential solidification.Subsequently,through changing the position of risers,adding a connecting channel between the risers,and setting blind risers at the U-shaped brackets,an optimized gating and feeding system was established to improve the quality of the casting.After optimization,the gas pore and shrinkage porosity defects of the leaf spring bracket casting are effectively eliminated.The experiment results with the optimized casting process are in good agreement with the numerical simulation,which verifies the validity of the finite element model in the shell mould casting.

Relationships between the surface quality of a single crystal copper ingot and the process parameters of a heated mould continuous casting method

The relationships between the surface quality of a single crystal copper ingot and the process parameters of heated mould continuous casting method were studied experimentally using our own design of horizontal heated mould continuous casting apparatus, and the mechanism by which process parameters affect the surface quality of a single crystal copper ingot is analyzed in the present paper. The results show that the process parameters affect the surface quality of a pure copper ingot by affecting the position of the liquid-solid interface in the mould. The position of the liquid-solid interface in the mould must be controlled carefully within an appropriate range, which is determined through a series of experiments, in order to gain a single crystal copper ingot with good surface quality.

Modeling of unsteadiness of fluid flows and level fluctuations in thin slab continuous casting moulds

Unsteady fluid flows and level fluctuations in a thin slab continuous casting mould have significant influence on product quality. In this study, the phenomena concerning transient flow features and free surface motions were analyzed by means of the large eddy simulation （LES） software with the smagorinsky SGS model--VisualCast （VCast） II, where the Simpler algorithm on a body-fitted mesh was used to resolve governing equations. A series of water analog experiments on the fluid flow and the surface wave in the moulds of thin slab continuous casting were also performed. The results of fluid regions, middle of vortex and level fluctuation from digital simulations were identical with the results of the water analog experiments.

Effects of several casting parameters on slag entrapment in mould( part A: water modeling)

The mechanism of slag entrapment in the mould was analyzed and the water modeling experiment was done according to the industrial manufacturing. The results show that the flow of the liquid steel becomes more active and the level fluctuation in the mould becomes bigger when the casting speed increases from 1.0 m/min to 1.2 m/min. So the control of slag entrapment in the mould becomes more difficult. When the depth of the nozzle increases from 30mm to 42. 5mm and the angle increases from 15~ downward to 30° downward, the level fluctuation in the mould becomes smaller and the slag entrapment in the mould also decreases. But the impact depth increases and the circumfluence vortex center moves downward, which is unfavorable for the flotation of gas bubbles and inclusions. Furthermore, the impact depth with side holes a （ 16.3 × 20mm2 ） and b （ 10 × 10 mm2 ） is almost equal, but a smaller level fluctuation can be obtained with side hole a.

Microstructure and mechanical properties of TiAl castings produced by zirconia ceramic mould

Owing to their low density and attractive high-temperature properties, gamma titanium aluminide alloys （TiAI alloys, hereafter） have significant potential application in the aerospace and automobile industries, in which these materials may replace the heavier nickel-based superalloys at service temperatures of 600 - 900℃. Investment casting of TiAI alloys has become the most promising cost-effective technique for the manufacturing of TiAI components. Ceramic moulds are fundamental to fabricating the TiAI casting components. In the present work, ceramic mould with a zirconia primary coat was designed and fabricated successfully. Investment casting of TiAI blades and tensile test of specimens was carried out to verify the correctness and feasibility of the proposed method. The tensile test results indicate that, at room temperature, the tensile strength and the elongation are about 450 MPa and 0.8%, respectively. At 700℃, the tensile strength decreases to about 410 MPa and the elongation increases to 2.7%. Microstructure and mechanical properties of investment cast TiAl alloy are discussed.

Effects of continuous casting mould fluxes on reducing longitudinal and star cracks on a slab surface

In the continuous casting production of medium carbon steel (whose mass fraction of carbon is 0.09 % to 0.16 %) and high strength low alloy steel (whose mass fraction of Mn is 0.90 % to 1.40 %), flecks occurring the most often are usually longitudinal and star cracks. In additional to the employment of a galvanized plate mould, two kinds of fluxes with special properties were studied and used to harmonize the conflicts between the function of heat transfer and lubrication. An industrial application revealed that the crystallizing temperature (Tc) and crystal ratio (R) of fluxes have a crucible effect on impeding the occurrence of above defects on a slab surface. In the case of slab section (180 to 240) mm(1000 to 1400) mm and casting speed Vc of (0.7 to 1.2) m/min, the optimized parameters of fluxes are Tc of (1170 to 1190) ℃, R of 80 % to 95 % for medium carbon steel, and Tc of (1100 to 1150) ℃, plus R of 40 % to 60 % for high strength low alloy steel.

An integration system for investment casting mould design of aeroengine turbine blade

An integration system was developed to satisfy the need of information integration in the process of designing, investment casting and monitoring aero-engine's turbo blade. The general architecture is detailed presented in this paper. The system mainly comprises of product master model, design information management, anti-deformation design of mould cavity, intelligence mould design and blade testing. The developed system can manage mould design and blade test data flow, optimize mould design process and achieve the goal of integration design.

Effect of mould material on aluminum alloy ingot quality under low frequency electromagnetic casting

With the aid of ANSYS software, the effect of different mould external part materials on magnetic flux density and electromagnetic body force in the liquid aluminum was investigated. Calculated results showed that magnetic flux density and electromagnetic body force in the aluminum melt are greatly increased when the external part of mould is made from A3 steel. A low-frequency electromagnetic casting 6063 aluminum alloy experiment was conducted in the laboratory with the current value of 120 A and frequency value of 15 Hz. The experiment showed that the microstructure and surface quality of ingots with mould outer part made from A3 steel under low-frequency electromagnetic field are better than that of ingots with mould outer part made from austenitic stainless steel. The surface of the ingots with mould outer part made from A3 steel is smooth and free from exudations and cold shut defects. The as-cast microstructure consists of fine, uniformly distributed equiaxed grains.

Performance analysis of cow dung as an eco-friendly additive material for sustainable moulding and casting

In the present work,an attempt is made to partially replace high cost silica sand with sustainable eco-friendly cow-dung.The practical utility of cow dung as an additive material that facilitates binding in sand moulds has been tested.The Taguchi method is used to plan and conduct nine experiments with three replicates each.Pareto analysis of variance study is performed to understand the practical significance of moulding sand variables,that is,percentage of cow dung,clay,water,and degree of ramming on sand mould properties.The conflicting multiple objective functions(maximize mould hardness,and minimize collapsibility and gas evolution)are optimized by utilizing the Data Envelopment Analysis Ranking(DEAR)method.The optimal parameters i.e.6%of clay,4%of water,5%of cow-dung and 4 numbers of ramming strokes are obtained by applying a hybrid Taguchi-DEAR method.These parameters show the best moulding properties are:mould hardness 55,gas evolution 5.9 ml·g-1,and collapsibility 470 g·cm-2.Thereafter,a Lovejoy coupling made of aluminium is cast in the sand mould prepared with cow dung and without cow dung,with the optimum set of parameters.The mechanical properties,surface finish,and microstructure of the casting cast with cow-dung are better than that without cowdung.

Computer Simulation of Mould Filling and Solidification of Castings

A finite volume based 3-D computer code which can simulate fluid flow during mould filling coupled with heat transfer as well as solidification has been developed in WTCM Foundry Center. The code can predict cold shut during mould filling, shrinkage defects during solidification and aid designing the casting system. Several experiments of filling vertical plate castings have been carried out. A heat resistant glass window has been used to observe the liquid metal flow behavior. Although the plate casting has a very simple geometry, the associated flow behavior is quite complex. Mould filling experiments carried out identical conditions never produce exactly the same results. The simulated results of the mould filling sequence and the temperature distribution have been compared with experiments. A good agreement has been achieved. The code has been used in foundries. A real application example is given which illustrates how to use computer simulation to aid designing the casting system. Sound castings based on computer aid designing have been produced. The process of designing castings by using simulation is completely different from the traditional way. The computer aided casting design offers the possibility to obtain a sound casting from the first time.

Recycling of Cristobalite Powder in Casting Mould

Cristobalite SiO2 can be obtained from the fused silica ceramic waste of ploysilicon plant, due to the phase conversion of fused silica to cristobalite during the process of polysilicon ingot. Cristobalite powder materials with high purity are manufactured by milling the discarded waste above. Thermal expansion rate of the cristobalite and gypsum bonding moulds were studied, which show that the thermal expansion of the cristobalite phase transition could effectively compensate for the shrinkage of the gypsum at the temperature between 200 ℃ and 400 ℃. Casting experiments with copper alloy show that the cristobalite can improve the thermal performance of moulds for precise casting of jewelry.

Mould filling ability and microstructure of aluminum alloy under electromagnetic die casting

In order to solve the mould filling problem of large thin walled aluminum alloy castings effectively, a new casting technology called electromagnetic die casting has been developed. Emphasis has laid on studying the mould filling ability and microstructure under the mentioned method. The results show that the mould filling ability of A357 is increasing continually with the increasing of the input voltage, that is, the magnetic induction intensity. The pressure head of the molten metal increases from the lowest one at the input of the mould to the highest one at the end of the mould while in a conventional mould the pressure head depends invariably on the sprue height. Under electromagnetic die casting, the grains of A357 alloy are refined, and the pattern of eutectic silicon of alloy changes from rough plate to smooth strip.

Theoretical and experimental analyses of continuous casting with soft-contacted mould (Ⅱ)—EMF calculation and experimental analyses

Coupling the quasi 3D numerical simulation of the electromagnetic field and the experiments with some metals, a series of phenomena in the processes of continuous casting with soft contacted mould was analyzed. Some theoretical and experimental models were presented, from which following results were obtained. 1) The electromagnetic force is related with electric conductivity of billet as a power function to 0.4. 2) The heat transfer between billet and mould is related with the contacting pressure, and it is a linear function for tin billet approximately. 3) The distance between initial solidification point and meniscus in billet is related with the surface magnetic flux density as a fourth root function. 4) The temperature gradient in the initial solidifying shell is reduced, which can decrease the tendency of hot tearing on the surface of billet, and increase the equiaxed crystal zone in billet. 5) The stronger the magnetic flux density is, the more shallow and the thinner the oscillation mark on the surface of billet is. 6) The depth of oscillation mark on the billet cast by the soft contacted mould can be reduced to about 10% in comparison with that on the billets cast by traditional mould. 7) In non dimensional condition, the average depth of the oscillation marks on the billets cast by the soft contacted mould decreases with increasing magnetic flux density on there as a complementary error function. [

Effects of several casting parameters on slag entrapment in mould (part B:numerical modeling)

Based on the effects of several casting parameters on slag entrapment in the mould （ water modeling）, the numerical modeling was researched. The results show that the flow field with a submerged nozzle section dimension of 65 mm ×80 mm is better than that with a submerged nozzle section dimension of 40 mm × 40 mm and is favorable for avoiding slag entrapment. In this paper, low surface velocity, small level fluctuation and proper impact depth can be achieved with a nozzle of an outlet angle of 25° and an immersion depth of 150 mm, or with a prototype nozzle of an outlet angle of 15° angle and an immersion depth of 150 mm.