Vacuum Counter-pressure Casting Research Articles

Optimizing the Microstructure and Mechanical Properties of Vacuum Counter-Pressure Casting ZL114A Aluminum Alloy via Ultrasonic Treatment

The effect of ultrasonic temperature on density, microstructure and mechanical properties of vacuum counter-pressure casting ZL114A alloy during solidification was investigated by optical microscopy (OM), scanning electron microscope (SEM) and a tensile test. The results show that compared with the traditional vacuum counter-pressure casting aluminum alloy, the primary phase and eutectic silicon of the alloy with ultrasonic treatment has been greatly refined due to the dendrites broken by ultrasonic vibration. However, the refining effect of ultrasonic treatment on vacuum counter-pressure casting aluminum alloy will be significantly affected by ultrasonic temperature. When the ultrasonic temperature increases from 680 °C to 720 °C, the primary phase is gradually refined, and the morphology of eutectic silicon also changes from coarse needle-like flakes to fine short rods. With a further increase in the ultrasonic temperature, the microstructure will coarse again. The tensile strength and elongation of vacuum counter-pressure casting ZL114A alloy increases first and then decreases with the increase of ultrasonic temperature. The optimal mechanical properties were achieved with tensile strength of 327 MPa and the elongation of 5.57% at ultrasonic temperature of 720 °C, which is 6.3% and 8.2%, respectively, higher than that of alloy without ultrasonic treatment.

Optimization of vacuum counter-pressure casting process for an aluminum alloy casing using numerical simulation and defect recognition techniques

Vacuum counter-pressure casting (VCPC) process is an effective forming process of producing components with complex thin-walled characteristics. In this study, a surrogate-based optimization method with five process parameters is used to reduce the shrinkage porosity defect during the VCPC process of a complicated thin-walled aluminum alloy casing. The prediction of the shrinkage porosity defect is implemented by using the numerical simulation of the VCPC process. In general, performing the optimization directly based on the casting simulation may not be practical due to the computational and time constraints. To mitigate this problem, the response surface model (RSM) constructed via computer experiments is employed to accurately approximate the functional relationship between the process parameters and the response variable which is defined as the area of defects in the defect image generated from the casting simulation. To measure the area of defects in the image, a histogram-based threshold segmentation approach is proposed to recognize and quantify the defects from the image. The optimization problem is subsequently formulated using a desirability function-based optimization method, and the objective function is estimated using the built RSMs. The final results indicate that a set of optimal process parameters with minimum defects can be obtained.

Effect of synergistic action of ultrasonic vibration and solidification pressure on tensile properties of vacuum counter-pressure casting aluminum alloy

The effect of synergistic action of ultrasonic vibration and solidification pressure on tensile properties of vacuum counter-pressure casting ZL114A alloys was studied systemically through testing and analyzing the tensile strength and elongation subjected to different ultrasonic powers and solidification pressures. The results indicate that the synergistic action of ultrasonic vibration and solidification pressure can result in the refinement of grains and improvement of tensile properties. Both the highest tensile strength and elongation of aluminum alloy were obtained under synergistic action of 600 W ultrasonic power and 350 kPa solidification pressure. Moreover, the tensile fracture morphology shows obvious ductile fracture characteristics. When the solidification pressure is lower than 300 kPa, the effect of ultrasonic power on tensile strength and elongation is more obvious, but when the solidification pressure is higher than 300 kPa, the effect of solidification pressure on tensile strength and elongation is greater. Meanwhile, the size and morphology of the eutectic silicon were improved significantly by the ultrasonic vibration and pressurized solidification. The strip and massive eutectic silicon phase are completely converted into small short rod-like and evenly distributed Si phases at the grain boundary of primary α-Al.

Density and solidification feeding model of vacuum counter-pressure cast aluminum alloy under grade-pressuring conditions

The density of vacuum counter-pressure cast aluminum alloy samples under grade-pressuring condition was studied. The effect of grade pressure difference and time on the density of aluminum alloys was discussed, and the solidification feeding model under grade-pressuring condition was established. The results indicate the grade-pressured solidification feeding ability of vacuum counter-pressure casting mainly depends on grade pressure difference and time. With the increase of grade pressure difference, the density of all the aluminum alloy samples increases, and the trend of change in density from the pouring gate to the top location is first decreasing gradually and then increasing. In addition, in obtaining the maximum density, the optimal grade-pressuring time is different for samples with different wall thicknesses, and the solidification time when the solid volume fraction of aluminum alloy reaches about 0.65 appears to be the optimal beginning time for grade-pressuring.

Microstructures and mechanical properties of vacuum counter-pressure casting A357 alloys solidified under grade-pressurising: effects of melt temperature

The effects of the melt temperature on the relative densities, microstructures and mechanical properties of vacuum counter-pressure casting A357 alloys solidified under grade-pressurising (200kPa) were investigated. The results indicated that the relative densities and mechanical properties of samples solidified under grade-pressurising were affected by the melt temperature (580–610°C). The optimal relative density and mechanical properties were achieved at a melt temperature of 590°C. The microstructures varied with the melt temperature as a result of the differences in the strengths of the feeding flow and dendrites. The powerful feeding flow caused by grade-pressurising solidification can induce stress on the dendrites, resulting in the collapse of the primary dendrite network to form equiaxed dendrites. Decreasing the feeding pressure proportionally to the solid volume fraction was proposed to obtain a suitable melt temperature for improving the density and refining the microstructure.

Effect of Vacuum Degree on Pinhole of Vacuum Counter-Pressure Casting Molten Aluminum Alloy

During vacuum counter-pressure casting, the vacuumization is an important stage for thin-wall and complicated aluminum alloy castings. Through testing and an analyzing numbers of pinhole and pinhole grade of aluminum alloy samples under different vacuum degree, the effect of vacuum degree on pinhole of vacuum counter- pressure casting molten aluminum alloy is studied. The results indicate vacuum degree has greater effect on pinhole of molten aluminum alloy in vacuumizing process. The smaller vacuum degree is, the more numbers of pinhole of the samples are, and the higher pinhole grade of the samples is. Therefore, when vacuum degree is small, pinhole of molten aluminum alloy appears easily. So the vacuum degree doesn’t choose too small, but for thin-wall and complicated aluminum alloy castings, the vacuum degree doesn’t choose too big either. Appropriate vacuum degree is from 20 KPa to 40 KPa.

Research of Casting Process about Cover and Pump Body of Tonghai Pump and Mechanical Properties Test

In order to obtain cover and pump body of tin bronze Tonghai pump that is dense and good pressure resistance,the casting mold of the cover of Tonghai pump is metal mold. The casting method of Tonghai pump is vacuum counter-pressure casting.The method of casting pump body of Tonghai pump is vacuum investment casting. This research is about reasonable casting process parameters of vacuum counter-pressure casting and vacuum investment casting.Finally qualified castings of cover and pump body of Tonghai pump can be obtained.

Fabrication of Continuous Nickel-Coated Carbon Fiber Reinforced Aluminum Matrix Composites Using Low Gas Pressure Infiltration Method

Based on the principle of vacuum counter-pressure casting, a low gas pressure infiltration technology was developed to fabricate the Ni-coated carbon fiber reinforced A357 alloy composites. The soundness and microstructure of the as-cast composites were investigated. The results show the relative density increases with the increase of melt temperature, while it firstly increases and then declines as the fiber temperature and infiltration pressure increased. The enhancement of melt and fiber temperature can eliminate the incomplete infiltration defects and improve the uniformity of fiber distribution. The insufficient infiltration pressure leads to some micro-pores in the matrix alloy. However, the over high fiber temperature and infiltration pressure may result in the separation of nickel coating and the fiber aggregation respectively, both of which are responsible for the partial un-infiltrated or insufficient filling defects. The appropriate infiltration parameters identified in this study could provide a reference for inhibition of the hazard interfacial reactions by optimizing the low gas pressure infiltration process.

Effects of sample thickness on microstructures and mechanical properties of A357 alloy

The effects of sample thickness on the density, microstructures and mechanical properties of as cast Al alloy were investigated. Microstructures were observed with a scanning electron microscope. Mechanical properties were studied at room temperature. The results show that the sample thickness has minor influence on the relative density of Al alloy. The obtained relative density up to ∼99·24% was confirmed that the vacuum counter–pressure casting has the excellent solidification mechanism. The microstructures were refined and the secondary dendrite arm spacing was decreased with the decrease in sample thickness, and the ultimate tensile strength, yield strength and elongation were improved. The ultimate tensile strength and elongation could be related to their secondary dendrite arm spacing using linear equations. With the increase in sample thickness, the quasi-cleavage fractures were increased and the number of dimples got an evident reduction in fracture surfaces.

Effect of Pressurizing Process on Molten Aluminum Alloy and Furnace Chamber Temperature of Vacuum Counter- Pressure Casting

In pressurizing process of vacuum counter-pressure casting, the pressurizing pressure and velocity are very important parameters. Through testing the change of molten aluminum alloy and furnace chamber temperature with the time at difference pressurizing pressure and velocity, the effect of pressurizing process on molten aluminum alloy and furnace chamber temperature of vacuum counter- pressure casting is studied. The results indicate the furnace chamber temperature reduces abruptly at beginning of pressurizing process, subsequently, it elevates to the initial temperature. Moreover, the change of the furnace chamber temperature is finished in the short time. But the change of molten aluminum alloy temperature is not obvious in pressurizing process. At identical pressurizing velocity, the change of the furnace chamber temperature is bigger with increase of pressurizing pressure. Similarly, at identical pressurizing pressure, the change of the furnace chamber temperature is bigger with increase of pressurizing velocity too. Moreover, the effect of pressurizing velocity on the furnace chamber temperature is bigger than pressurizing pressure, and the change of the furnace chamber temperature don’t have effect on the change of molten aluminum alloy temperature.

Study on Pressurizing Velocity and Model of Vacuum Counter-Pressure Filling Process

During filling process of vacuum counter-pressure casting, the pressurizing velocity is one of the most important parameters, and it affects whole filling process of molten metal and the quality of castings, the pressurizing velocity must be reasonably controlled and chosen. Through analyzing the pressurizing velocity of vacuum counter-pressure casting filling process, the results show that pressurizing velocity is related with absolute temperature of down kettle gas, radius of rising tube, initial volume of down kettle, height from original position of molten metal to top of rising tube and gas flux. When other conditions are same during filling process of vacuum counter-pressure casting, pressurizing velocity is proportional to gas flux, and it is linear. Meanwhile, through experimental verification for relationship of pressurizing velocity with gas flux, their actual relationships and mathematical models are obtained, and correction coefficient is determined at the range from 0.95 to 0.98.

Effects of Gating System on the Flow Behaviors during Vacuum Counter Pressure Casting Thin Wall Aluminum Alloy

The flow behaviors of molten Al alloy in sand mould cavity with varied gating system were simulated under vacuum counter-pressure casting and the ingate velocity was predicted using a software package. At same process conditions, the flow behaviors were investigated using electrode contact method. The comparison between the simulated results and the investigated results shows that a good agreement is achieved. The ingate flow velocity exceeding critical velocity and large velocity deviation are detected during filling mould withⅠtypes gating system, resulting in turbulent flow behavior. Whereas, flow behaviors take on stable flow pattern during filling the other mould cavity, although some differences of flow behaviors are present. The small ingate flow velocity and velocity deviation during filling mould cavity with Ⅲ type gating system may be conduce the more stable flow pattern thanⅡtype gating system.

Effect of holding pressure on the microstructure of vacuum counter-pressure casting aluminum alloy

The effect of holding pressure on the microstructure of vacuum counter-pressure casting aluminum alloy was analyzed by observing the changes of the Si phase size and alloy density. The results show that with the increasing of holding pressure of vacuum counter-pressure casting, the extrusion and infiltration ability among dendrites is enhanced and the microstructure of prepared alloy samples at the same location becomes finer, more uniform and denser. Under the same holding pressure, the smallest extrusion and infiltration ability takes place at the middle of sample. Accordingly, from the pouring gate to middle, the microstructure of vacuum counter-pressure casting aluminum alloy sample becomes coarser, more non-uniform and less dense, while the microstructure from the middle to top becomes finer, more uniform and denser.