Effect of melt-to-solid volume ratio and preheating temperature on Mg/Al bimetals interface by centrifugal casting

Compound casting is an efficient method for bonding dissimilar metals,in which a dramatic reaction can occur between the melt and solid.The centrifugal casting process,a type of compound casting,was applied to cast Al/Mg dissimilar bimetals.Magnesium melt was poured at 700 °C,with melt-to-solid volume ratios(Vm/Vs) of 1.5 and 3,into a preheated hollow aluminum cylinder.The preheating temperatures of the solid part were 320,400,and 450 °C,and the constant rotational speed was 1,600 rpm.The cast parts were kept inside the casting machine until reaching the cooling temperature of 150 °C.The result showed that an increase in preheating temperature from 320 to 450 °C led to an enhanced reaction layer thickness.In addition,an increase in the Vm/Vs from 1.5 to 3 resulted in raising the interface thickness from 1.2 to 1.8 mm.Moreover,the interface was not continuously formed when a Vm/Vs of 3 was selected.In this case,the force of contraction overcame the resultant acting force on the interface.An interface formed at the volume ratio of 1.5 was examined using scanning electron microscopy(SEM) equipped with energy-dispersive X-ray spectroscopy(EDS),and the results demonstrated the formation of Al_(3)Mg_(2),Al_(12)Mg_(17) and(δ+Al_(12)Mg_(17)) eutectic structures in the interface.

Centrifugal casting processes of manufacturing in situ functionally gradient composite materials of Al-19Si-5Mg alloy

Cylindrical components of in situ functionally gradient composite materials of Al-19Si-5Mg alloy were manufactured by centrifugal casting. Microstructure characteristics of the manufactured components were observed and the effects of the used process factors on these characteristics were analyzed. The results of observations shows that, in thickness, the components possess microstructures accumulating lots of Mg2Si particles and a portion of primary silicon particles in the inner layer, a little MgzSi and primary silicon particles in the outer layer, and without any Mg2Si and primary silicon particle in the middle layer. The results of the analysis indicate that the rotation rate of centrifugal casting, mould temperature, and melt pouring temperature have evidently affected the accumulation of the second phase particles. Also, the higher the centrifugal rotation rate, mould temperature, and melt pouring temperature are, the more evident in the inner layer the degree of accumulation of Mg2Si and primary silicon particles is.

A study on centrifugal casting of high speed steel roll

High speed steel (HSS) rolls can replace traditional rolls such as alloyed cast iron rolls and powder metallurgical (PM) hard alloy rolls. The main reasons for the replacement are that the wear resistance of low-cost alloyed cast iron rolls is poor and the cost of high-quality PM hard alloy rolls is very high. By means of centrifugal casting, HSS rolls having excellent wear resistance have been manufactured. The hardness of the HSS roll is 6.5~67 HRC, the range of variation is smaller than 2 HRC and its impact toughness is 15 J/cm2. The wear rate of HSS rolls used in the pre-finishing stands of high-speed hot wire-rod rolling mill reaches 2.5×10-4mm per ton steel. Furthermore, the manufacturing cost of HSS rolls is significantly lower than that of PM hard alloy rolls; it is only 30 percent of that of PM hard alloy rolls.

Microstructural evolution and enhanced mechanical properties of Mg?Gd?Y?Zn?Zr alloy via centrifugal casting, ring-rolling and aging

A ring-shaped Mg?8.5 Gd?4 Y?1 Zn?0.4 Zr(wt%) alloy was manufactured via centrifugal casting and ring-rolling process. The effects of accumulative ring-rolling reduction amount on the microstructure, texture, and tensile properties of the alloy were investigated. The results indicate that the microstructure of centrifugal cast alloy consists of equiaxed grains and network-like eutectic structure present at grain boundaries. The ring-rolled alloy exhibits a characteristic bimodal microstructure composed of fine dynamic recrystallized(DRXed) grains with weak basal texture and coarse un-DRXed grains with strong basal texture, along with the presence of LPSO phase. With increasing amount of accumulative ring-rolling reduction, the coarse un-DRXed grains are refined via the formation of increasing amount of fine DRXed grains. Meanwhile, the dynamic precipitation of Mg5 RE phase occurs, generating a dispersion strengthening effect. A superior combination of strength and ductility is achieved in the ring-rolled alloy after an accumulative rolling reduction of 80%. The tensile strength of this ring-rolled alloy after peak aging is further enhanced, reaching 511 MPa, while keeping a reasonable ductility. The salient strengthening mechanisms identified include the grain boundary strengthening of fine DRXed grains, dispersion strengthening of dynamic precipitated Mg;RE phase, short fiber strengthening of LPSO lamellae/rods, and precipitation strengthening of nano-sized prismatic β precipitates and basal γ precipitates.

Microstructure and Mechanical Behavior of in Situ Primary Si/Mg_2Si Locally Reinforced Aluminum Matrix Composites Piston by Centrifugal Casting

Al-Si pistons are frequently damaged by burning piston top surface due to elevated combustion temperature, and by rubbing the first ring groove against the engine cylinder liner. To prevent piston from these damages, some technologies were invented, such as mounting high Ni cast iron ring around the first ring groove in Al alloy piston body and thermal resistant steel on piston top surface, and fabricating Al composite pistons by squeeze casting for enhancing the whole or local piston performance. In this paper, composite pistons locally reinforced with in situ primary Si and primary Mg2Si particles are fabricated by centrifugal casting. The microstructure characteristics, hardness and wear resistance of the composite piston are investigated and the motion characteristic of the in situ particles in centrifugal field is analyzed. The results of the experiments show that primary Si and Mg2Si particles mix up with each other in melt and segregate at the regions of piston top and piston ring grooves under the effect of centrifugal force. Particulate reinforced regions have a higher hardness and better wear resistance compared with the unreinforced regions and this performance increases after heat treatment. The analysis result of particle movement shows that, primary Si and primary Mg2Si particles move at approximately the same velocity in the centrifugal field, because of the growth of primary Si and fusion after colliding between primary Si particles, which compromised the velocity difference of primary Si and primary Mg2Si particles caused by the difference of their densities. Research results have some theory significance and applicative value of project in development of new aluminum matrix composites piston products.

Structure and Mechanical Properties of Al-based Gradient Composites Reinforced with Primary Si and Mg_2Si Particles through Centrifugal Casting

The structure and mechanical properties of a new type of Al-based discontinuous gradient composites prepared by using the ternary AI-19Si-5Mg alloys as the raw material adopting the centrifugal casting method were investigated. Structurally, the composites are divided into two zones： a reinforced zone with the high volume fraction of primary Si and Mg2Si particles and an unreinforced zone with no or a few particles. In the reinforced zone, the primary particles are evenly distributed, with the sizes of the primary Si particles 80-120 μm, and that of primary Mg2Si particles 20-50 μm. The properties test results show the reinforced zone has higher Rockwell hardness and better wear resistance than the unreinforced zone, due to the complementary reinforcement relationship between the primary Si and Mg2Si particles and their high volume fraction.

Forming Mechanism of Gaseous Defect in Ti-48Al-2Cr-2Nb Exhaust Valves Formed with Permanent Mold Centrifugal Casting Method

A method combining theoretical analysis with experiment is adopted and the flowing process of Ti-48A1-2Cr-2Nb alloy melt poured in a permanent mould during the centrifugal casting process has been analyzed. A mathematical model of the filling process is established and the forming mechanism of internal gaseous defect is summarized. The results of calculation show that the melt fills the mould with varying cross-section area and inclined angle. The filling speed of the cross-section is a function of filling time. The cross-section area is directly proportional to the filling speed and the inclined angle is inversely proportional to the filling speed at a given rotating speed of the platform. Both of them changes more obvious near the mould entrance. The gaseous defect can be formed in several ways and the centrifugal field has an important influence on the formation of the defect. In addition, the filling process in centrifugal field has been verified by wax experiments and the theoretical analysis are consistent with experimental results.

Analysis of filling process of Ti6Al4V alloy melt poured in permanent mold during centrifugal casting process

Ti6Al4V hip joint was foundered and the filling process of the melt poured in permanent mould during the centrifugal casting process was analyzed and the mathematical model of the filling process was established. Furthermore, the mathematical model was validated with a wax model experiment. Calculating results show that the centrifugal field has an important influence on the filling process and the melt fills the mould with variational cross sectional area and inclined angle. The cross sectional area is in inverse proportion to the filling speed and its decreasing speed becomes fast with increasing rotating speed. The tangential value of the melt cross sectional free surface inclined angle is in direct proportion to the filling speed and the inclined angle increases with the filling length. Change curves of the cross sectional inclined angle and area were obtained by the wax model experiment when the rotating speeds were 60, 90 and 120 r/min respectively, which shows that the mathematical model is consistent with the experimental results. [

ANALYSIS OF FLUID FIELD OF LIQUID METAL IN ELECTROMAGNETIC CENTRIFUGAL CASTING

Navier-Stokes equation and Lorentz force equation are used to calculate the fluid field of liquid metal of electromagnetic centrifugal casting (EMCC) in this paper. A field equation is given, which shows the azimuthal velocity closely relates to electrical conductivity, magnetic density, viscosity of liquid metal and radius of casting. The results show that the stationary magnetic field can effectively restrain the fluid flow and the relative velocity between liquid metal and casting mould and the velocity gradient at solid / liquid interface increases with rising magnetic density, which has a great effect on the solidification of liquid metal and crystal growth characteristics.

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.

Development of centrifugal casting high speed steel rolls

The present study aims at developing the high speed steel (HSS) as rollmaterials to replace the traditional roll materials such as the alloy cast iron and powdermetallurgical (PM) hard alloy. The HSS roll billet was formed by centrifugal casting, and the billetwas rough machined alter soften annealing heat treatment, then it was quenched and tempered to getsuitable hardness and toughness. After that the HSS roll was finish machined to the final dimensionof phi 285 mm in the outer diameter, phi 160 mm in the inner diameter and 120 mm in width and itssurface hardness was tested. Finally the HSS roll was used in high speed wire rod mill. The testresults show that a high and homogeneous hardness can obtain on the work surface of HSS rolls, thesurface hardness is 63-65HRC and its variation is smaller than 2HRC. The impact toughness of thiskind of HSS is about 16 J/cm^2. The results of on-line service investigation in high speed wire rodmill indicate that the HSS rolls have excellent wear resistance, the steel rolling quantity per mmof HSS rolls is 3120 t, the service life-span of HSS rolls is 4 times longer than that of highchromium cast iron rolls and it is close to that of the PM hard alloy rolls. The manufacturingburden of HSS rolls is obviously lower than that of the PM hard alloy rolls, it is only 25 percentof that of the PM hard alloy rolls.

THEORETICAL ANALYSIS OF PARTICLE DISTRIBUTION IN GRADIENT COMPOSITE BY CENTRIFUGAL CASTING

A theoretical analysis was presented to produce gradient composite by centrifugal casting. Particle movement in liquid metal is described and gradient distribution of particles in composite is calculated in a centrifugal field. The factors affected the gradient distribution are discussed in detail. There exist composite zone and blank zone in gradient composite, which was proved by experiments. Finally, a theoretical analysis is given to explain the above mentioned particle distribution.

Effects of Pouring Temperature on Interfacial Reaction between Ti-47-5Al-2-5V-1Cr Alloy and Mold during Centrifugal Casting

Pouring temperature and time are the most important influencing factors on interfacial reaction during the centrifugal casting. When cast at high temperatures, the crucible becomes brittle and prone to cracking, and shows a low stability. In this paper, we studied the centrifugal casting of Ti-47.5-Al-2.5V-1Cr alloy, and explored the effects of pouring temperature on the interfacial reaction. Castings at 1 600, 1 650, and 1 700 ℃ were obtained by controlling the other parameters constant in the experiments. The microstructure, elemental distribution, thickness of the reaction layer and phase composition of the castings at the interface were studied. The results show that the thickness at the interfacial reaction layer is increased by raising the pouring temperature. The elements in the mold and the matrix were double-diffused and reacted at the interface during the casting process, and formed solid solutions with the precipitation of many new phases such as AlOand TiO. The roughness of interface structure and layer thickness of reaction increase with the rise of temperature, and the interfacial reaction is more intense. There is a minimum layer thickness of the reaction layer that is 80 μm when the temperature is 1 600 ℃.

Microstructures in Centrifugal Casting of SiC_p/AlSi9Mg Composites with Different Mould Rotation Speeds

Two ingots were produced by centrifugal casting at mould rotational speeds of 600 rpm and 800 rpm using 20 vol%SiC p /AlSi9Mg composite melt,respectively.The microstructure along the radial direction of cross-sectional sample of ingots was presented.SiC particles migrated towards the external circumference of the tube,and the distribution of SiC particles became uniform under centrifugal force.Voids in 20 vol%SiC p /AlSi9Mg composite melt migrated towards the inner circumference of the tube.The quantitative analysis results indicated that not only SiC particles but also primaryαphases segregated greatly in centrifugal casting resulting from the transportation behavior of constitutions with different densities in the SiC p /AlSi9Mg composite melt.In addition,the eutectic Si was broken owing to the motion of SiC p /AlSi9Mg composite melt during centrifugal casting.

Analysis of Molten Metal Distribution in the Mold of a Horizontal Centrifugal Casting

It is numerically studied the influence of the angular velocity, the molten metal viscosity, and the mold wall roughness on the molten metal distribution in the mold of a horizontal centrifugal casting process. The undesirable raining phenomenon sometimes arises in horizontal centrifugal casting. It occurs when the molten metal rains or falls from the top of the mold to the bottom while the mold is rotating. Using Computational Fluid Dynamics simulations, the conditions for the emergence of the raining phenomenon were explored in this work. For the system considered, angular velocities less than 77 rad/s cause the emergence of the raining phenomenon and accumulation of the molten metal in the lower part of the mold, whereas angular velocities greater than 77 rad/s produce a constant thickness of the molten metal and prevent raining.

Centrifugal Casting of High Speed Steel/Nodular Cast Iron Compound Roll Collar

The centrifugal casting of compound HSS/nodular cast iron roll collar was studied,and the factors affecting transition zone quality were analyzed.The pouring temperature and interval in pouring are the main factors affecting transition zone quality.By controlling process parameter and flux adding during casting,high quality roll collar was obtained.The cause,why in the casting of HSS part,segregation appears easily,was analyzed and the countermeasure eliminating segregation was put forward,the measure eliminating heat treatment crackling was also put forward.

Effect of the Density of Molten Metal on the Raining Phenomenon in Horizontal Centrifugal Casting

In this work the influence of the density of the molten metal on the emergence of the raining phenomenon in the horizontal centrifugal casting process is numerically studied. Transient 2D numerical simulations were carried out using Computational Fluid Dynamics software. Three molten metals with different density, namely aluminum, iron and lead, and three angular frequencies, namely 50, 66 and 77 rad/s were considered. It is found that the density of the molten metal significantly affects the emergence, transient or permanent, of the rain phenomenon. However, the magnitude and duration of the rain phenomenon depend on the angular frequency of the rotating mold. Likewise, since gravitational forces affect the metal according to its density, the value of the critical rotation speed of the mold is also affected.

Melt flow,solidification structures,and defects in 316 L steel strips produced by vertical centrifugal casting

Vertical centrifugal casting can significantly enhance the filling capability of molten metals,enabling the production of complex thin-walled castings at near-rapid cooling rates.In this study,the melt flow,solidification structures,and defects in 316 L steel cast strips with a geometry of 80 mm×60 mm×2.5 mm produced by vertical centrifugal casting were numerically and experimentally analyzed under different rotation speeds.With gradually increasing the rotation speed from 150 r/min to 900 r/min,the simulated results showed the shortest filling time and minimum porosity volume in the cast strip at a rotation speed of 600 r/min.Since a strong turbulent flow was generated by the rotation of the mold cavity during the filling process,experimental results showed that a“non-dendritic”structure was obtained in 316 L cast strip when centrifugal force was involved,whereas the typical dendritic structure was observed in the reference sample without rotation.Most areas of the cast strip exhibited one-dimensional cooling,but three-sided cooling appeared near the side of the cast strip.Moreover,the pores and cracks in the 316 L strips were detected by computed tomography scanning and analyzed with the corresponding numerical simulations.Results indicated the existence of an optimal rotational speed for producing cast strips with minimal casting defects.This study provides a better understanding of the filling and solidification processes of strips produced by vertical centrifugal casting.

High-temperature phase transition behavior and magnetocaloric effect in a sub-rapidly solidified La–Fe–Si plate produced by centrifugal casting

A sub-rapidly solidified LaFe11.6Si1.4 plate was fabricated directly from liquid by centrifugal casting method. The phase constitution, microstructure and magnetocaloric effect were investigated using backscatter scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and phys- ical property measurement system. When the plate was annealed at 1373 K, rl phase was formed by a solid-state peritectoid reaction. A first-order magnetic phase transition occurred in the vicinity of 188 K, and the effective refrigeration capacities reached 203.5J/kg and 209.7J/kg in plates annealed for I h and 3 h, respectively, under a magnetic field change of 3T. It is suggested that centrifugal casting may become a new approach to prepare high-performance La-Fe-Si magnetocaloric plates for prac- tical applications, which could largely accelerate the formation of rl phase during high-temperature heat-treatment process due to refined and homogeneous honeycombed microstructure.

Chemical Compositions,Microstructure and Mechanical Properties of Roll Core used Ductile Iron in Centrifugal Casting Composite Rolls

The industrial manufacture processes of three kinds of roll core used ductile irons have been investigated via systematical experiments. EfFects of the ratio of C/Si, pig iron, nodularizer and alloying method on the microstructure and mechanical properties of the heavy section ductile iron have been analyzed. It has been found that when treated with RE-Mg plus Sb, high quality nodular castings can be produced even if much anti spheroidizing alloy elements are included in the pig iron. The alloy element Sb played an important role in the control of graphite morphology.