Porosity In Castings Research Articles

The effect of unintended porosity on the first compressive stress maximum of alumina hollow sphere-filled bimodal composite metal foams

Bimodal composite metal foams made from Al99.5 aluminium and quasi-eutectic Sr-modified AlSi12 matrix were investigated, where the bimodality was introduced by two alumina hollow sphere sets with nominal diameters of Ø7.0 and Ø2.4 mm in various volume concentrations. The research aimed to determine the effect of the cell structure (especially the unintended porosity) on the first compressive stress maximum, depending on the applied matrix material. The various features of the cell structure were quantitatively measured in composite metal foams by filtering raw computed tomography analysis data. The casting porosity, the wetting porosity, the porosity from the various-sized hollow spheres, and the partially matrix-filled hollow spheres have been successfully distinguished based on volumetric and geometrical conditions, such as sphericity and compactness. The unintended porosity (as the sum of the casting porosity and the wetting porosity) influences the first compressive stress maximum of the Al99.5 matrix composite metal foams. In contrast, for the AlSi12Sr bimodal foams, the results correlated with the total porosity values. The first compressive stress maximum could be estimated well from the compressive yield strength of the matrix and the total porosity of the foam.

Optimizing Factors affecting gas porosity in GDC of Al-Si (A356) Alloy using Taguchi’s DOE

Aluminium alloys find extensive use in various applications because of its advantage of strength-to-weight ratio,. However, the casting process introduces susceptibility to defects, and managing all parameters proves to be a complex task. Casting rejections often stem from one or more defects, with mold parameters, filling, and solidification processes being key contributors. When the molten metal of the Al-Si (A356) alloy is exposed to the atmosphere in a holding furnace, it develops an oxide layer on its surface. Turbulence in the molten metal leads to the formation of a double oxide layer, also known as bifilms. Gas entrainment occurs due to the turbulent movement of metal, resulting in the entrapment of gas in the molten metal and ultimately causing gas porosity in the final casting. Gas entrapment during the filling process leads to gas porosities during the solidification phase.This study aims to comprehend the factors influencing the formation of gas entrapment during the casting of the aluminium alloy Al-Si (A356). The experimental investigation utilizes Taguchi’s Design of Experiments (DOE) to explore the impacts of parameters such as pouring temperature (PoT), degassing time (DgT), and volume in the holding furnace (VoH) on the formation of gas porosity in casting [8].An experimental setup was created to produce tensile test rods and reduced pressure test (RPT) samples. The results were validated using the mechanical properties of the tensile test samples and the density of the Reduced Pressure Test (RPT) samples. Better the mechanical properties, fewer will be the defects in castings. Taguchi’s DOE is applied to analyse the results. The experimental findings indicate that a pouring temperature at level 1 (710°C), degassing time at level 1 (10 minutes), and volume in the holding furnace at level 1 (>450 kg) yield favourable castings. Confirmatory tests were conducted to validate the results, and they aligned with the experimental data.

Effect of Gating System Design on the Quality of Aluminum Alloy Castings

In this paper, a naturally pressurized gating system has been designed to reduce the turbulence of the melt during casting. The influence of gate dimensions, foam filters, a trident gate and a vortex element were evaluated. Their effect on melt velocity, flow characteristics, number of oxides, casting properties and mechanical properties were observed. ProCAST Simulation software v.2023 and a water flow test were also evaluated to assist in the experimental evaluation of the castings. Melts showed a relationship between melt velocity and porosity of castings. Quantitative evaluation of the surface porosity showed a trend of decreasing porosity with decreasing melt velocity. The greatest reduction in the melt velocity was achieved by a M4 design, which was associated with the highest reduction in the oxides. The pores analyzed proved the presence of oxide layers on their inner surface and a possible theory of pore formation when the initiator of porosity is entrained double oxide layers. The best metal yield was achieved with M1, but the difference between M2 and M4 was negligible (2–5% yield difference), so it can be stated that the beneficial effect of the M4 design in providing the best quality castings is not negated by the increase in metal yield.

Criterion assessment of shrinkage porosity formation in castings

A method for calculating of the critical value of the porosity criterion developed at the Department of Foundry Technologies of Bauman Moscow State Technical University is proposed. The methodology is based on a computational experiment that allows us to determine with a high degree of probability the conditions for the formation of shrinkage porosity in castings, taking into account the thermophysical properties of the mould and the alloy.

Effect of refractory aggregate shape on the porosity of A356 alloy castings in lost foam casting

Effect of refractory aggregate shape on the porosity of A356 alloy castings in lost foam casting

Influence of plunger motion profile of high pressure die casting on the casting porosity and solidification rate

Influence of plunger motion profile of high pressure die casting on the casting porosity and solidification rate

Effect of barbotage refining time and recycled scrap content on the microstructure of EN AC 44200 alloy

The article presents the results of research on the effect of the barbotage refining time and recycled scrap content on selected properties, the microstructure and the degree of gasification of the EN AC 44200 alloy (EN AC-AlSi12). The input material consisted of various proportions of pure ingots and scrap; the scrap contents were 80%, 70% and 60%, respectively. Each batch of material was subjected to different refining times, which were 0, 7, 9 and 15 min, respectively. Microstructure studies were conducted with the techniques of light and scanning electron microscopy. Additionally, the distribution of pores in the volume of the material and their proportion were determined by means of the X-ray computed tomography method. In addition, the hardness and degree of gasification depending on the refining time were performed. It was proved that the refining process fosters homogenization of the microstructure and reduces porosity. Moreover, extending the refining time has a positive effect on reducing the porosity of thin-walled castings and reducing the level of outgassing of the alloy.

Analysis of Factor Effects in Process of Vertical Centrifugal Casting

ABSTRACT The effects of mold rotation speed, pouring temperature, preheating mold temperature, pouring rate and coating thickness on the solidification time, shrinkage porosity and melt velocity in vertical centrifugal casting were investigated. To minimize computation time and obtain adequate estimate of the effects, a Fractional Two – Level Factorial Design 2(5–1) was applied. The results were obtained by numerical simulations using ProCAST software. The regression model was developed using Design Expert software. The analysis of variance revealed that the coating thickness had the most pronounced effect on the solidification time and shrinkage porosity. Finally, the procedure for selecting the optimal factors was carried out by application of multi objective optimization. The shortest solidification time was 20.68 s, while the shrinkage porosity was negligible, and it was achieved with the highest value of mold rotation speed and the lowest values of pouring temperature, preheating mold temperature, pouring rate and coating thickness.

Effect of shell mold thickness and insulating wool pattern on internal porosity in investment casting of vortex flow meter

Effect of shell mold thickness and insulating wool pattern on internal porosity in investment casting of vortex flow meter

Pengaruh variasi ketebalan saluran dan temperatur tuang terhadap fluiditas dan porositas hasil pengecoran kuningan pada pengecoran evaporatif

The development of foundry technology continues to grow along with the increasingly complex needs for making products based on art and culture, one of which is sclupture. Evaporative casting based on non-permanent patterns made of polystyrene foam, with the advantage of precision casting results in complex shapes. The purpose of this study was to determine how variations in the pouring channel and pouring temperature affect the fluidity and porosity of brass castings in evaporative casting. Casting was carried out in castings with thicknesses of 1.5, 2, 3, 4, and 5 mm at pouring temperatures of 900°C, 950°C, and 1000°C using brass with a composition of Cu60% and Zn40%. The highest fluidity was found at a pattern density of 0.012 gr/cm3 at a pouring temperature of 1000°C with a flow length of 150 mm, while the lowest fluidity was obtained at a pattern density of 0.016 gr/cm3 at a pouring temperature of 900°C with a flow length of 13 mm. The results of scanning electron microscope (SEM) observations can be observed in spesimens with a density of polystyrene foam and a high casting temperature, an increase in the porosity formed.

Identifying Critical Defect Sizes From Pore Clusters in Nickel-based Superalloys Using Automated Analysis and Casting Simulation

Porosity can form during investment casting as a result of the solidification conditions. Significant porosity can result in agglomerations (pore clusters) which are a primary crack initiation source and can result in reduced fatigue life of Nickel-based superalloys. Such clusters of porosity are today conventionally measured using 2D micrographs. An approach to accurately predict and analyze casting porosity from 2D cuts while facing in reality a 3D shape problem is currently missing. In this work, an approach that combines automation and simulation to assess the representative pore dimension, their interconnectivity and the porosity position is presented. On a LPT blade made of IN100, the porosity percentage and Feret diameter have been measured in multiple cuts and the porosity was found to be in the range of 0.88 to 5.4 pct. From the same micrographs the critical defect sizes were estimated with an automated tool to be in the range of 200 to 1800 mum. The simulated shrinkage porosity for the same part, was predicted to be in the range of 1.67 to 2.33 pct. This study shows that the scaling factor between the pore Feret diameter and the critical pore size is equal to 2.9, in accordance to the proportionality of critical pores size clusters calculated from a 2D and 3D dataset. Finally, the simulated casting porosity was compared to that measured on cast blades in critical regions and the predictive accuracy is discussed in detail.

The impact on the cost of making high pressure die castings with multi-cavity die and vacuum assistance

In view of the increasing prices of energy and charge materials, it is necessary to optimize the costs of making castings. Tests were carried out on the possibility of making castings in a pressure die with an increased number of cavities with the required tightness of the casting. The tests were carried out on castings made in the High Pressure Die Casting process and with the use of the Vacuum System. The research included optimization of the pressure die design through selection of casting parameters and CT tests and microstructure. The results of the tests showed that it is possible to increase the number of pressure die cavities and to obtain the required level of casting porosity, provided that the Vacuum system is used. The amount of gas porosity in castings can be significantly reduced from 4% at atmospheric pressure to 1% at a vacuum of 300 mbar.

INFLUENCE OF DIE CASTING SPEED ON PROPERTIES OF CASTING BASED ON AL-SI ALLOYS

The paper focuses on the research of the influence of chosen technological parameters of die casting on the selected mechanical properties of castings based on Al-Si alloys. The experiments conducted within the frame of the practical part examined the plunger pressing speed in the mould cavity influencing the mechanical properties of a casting which were represented by ultimate tensile strength and percentage share of porosity of Al-Si castings. Plunger pressing speed is closely related to mould cavity filling mode which affected the final porosity of casting. In the case of increased percentage porosity share, the ultimate tensile strength decrease was detected due to the reduction of the cross-section area of the casting. The increase in percentage porosity share in the casting was caused by the increase in plunger pressing speed. To achieve the desired quality of castings, higher production efficiency, and reduced occurrence of faulty pieces during production, an optimal set of technological parameters of die casting is inevitable.

Optimization of centrifugal casting process parameters by Taguchi method to reduce shrinkage porosity ratio of K417 superalloy

The process parameters were optimized by simulation and verification experiments using orthogonal experimental design and the Taguchi method to lessen the tendency of significant shrinkage porosity in the centrifugal cast ring parts of K417 nickel-based superalloy. Advanced Porosity Model (APM) in ProCAST was used to predict the shrinkage porosity of centrifugal castings, and the effects of centrifugal speed, pouring speed, pouring temperature and preheating temperature of the mold were investigated on the shrinkage porosity ratio of the castings. According to the results, the parameter that has the greatest influence on the shrinkage porosity ratio of centrifugal casting is the centrifuge speed, followed by the preheating temperature of the mold, and the pouring temperature and pouring speed have relatively small effects on it. The optimized parameters were proposed as follows: centrifugal speed of 500 r/min, pouring speed of 225 mm/s, pouring temperature of 1400[Formula: see text], and mold preheating temperature of 50[Formula: see text], which could effectively reduce the formation of shrinkage porosity of the K417 centrifugal casting rings.

Procedure of Eliminating Porosity in Grey Cast Iron with Low Sulphur Content.

This study shows that the inoculation process of a molten alloy is crucial in disposing of porosity-type defects. A thermal analysis is used to assess the physico-chemical state of a molten alloy, which can be an indicator of the inoculation effect. A modern thermal analysis should be able to perform a quick data-analysis and provide information about any possible problems in a casting if it is poured with the analysed alloy. The time of the transmission of this information depends on whether we can make a decision and introduce changes to the metallurgical process. An important piece of information that can be obtained in this way is a message about the possibility of the appearance of porosity in a cast iron casting. In such a situation, an operator can react by applying an additional dose of inoculant. The porosity that is indicated by the thermal analysis systems can be either gaseous or shrinkage in nature. The research that is presented in this paper is based on two industrial castings that are made of cast iron with reduced sulphur content, in which shrinkage porosity occurred and was detected during the mechanical machining of the castings. As a result of laboratory tests in which iron powder was introduced along with an inoculant, a mixture was developed that, when applied under industrial conditions, eliminated the porosity defects by increasing the number of austenite dendrites. The ITACA thermal analysis system was used at each stage of the research, which allowed for the faster and more precise determination of the appropriate amount of the inoculant mixture that was used.

Effect of steel strip feeding on the columnar-equiaxed solidification in a large continuous casting round bloom

The steel strip feeding process can effectively improve the macrosegregation, central porosity, shrinkage, cracking, and other defects of continuous casting (CC) round blooms. Based on the volume-averaged method, a three-phase mix columnar-equiaxed solidification model is established, which considers the nucleation, growth of the columnar and equiaxed crystals, deposition of equiaxed crystals, and transmission of solutes. The effect of the feeding strip on the temperature, velocity, phase distribution, and macrosegregation distribution in a large vertical CC round bloom was studied. The results show that the CC bloom shell is built by columnar crystals, and equiaxed crystals fabricate the central zone. The feeding of the steel strip enhanced the flow inside the liquid core, which changed the flow direction of the center and end of the liquid core. The liquid phase and the temperature field display a similar distribution, and the liquid core and V-shaped high-temperature zone will gradually shorten with the increasing feeding ratio. A highly consistent distribution of the phase and the macrosegregation was found, and the increase in feeding ratio promotes columnar-to-equiaxed transformation (CET) and improves macrosegregation. Compared with no feeding strip, the extreme values of the macrosegregation index of 1.0% feeding ratio decreased by 37.1%, and the CET point at the sectional radius increased by 17.39%.

Optimization of investment casting process for K477 superalloy aero-engine turbine nozzle by simulation and experiment

In order to reduce the shrinkage porosity of nickel-based superalloy castings in the investment casting process, the effects of different gating systems on mold filling, solidification process, and prediction of shrinkage porosity of aero-engine turbine nozzle castings were investigated by simulation and experimental methods. Results show that the design of the vertical runner would cause greater turbulence of the melt in the riser during the mold filling process, and the outer runner is not necessary. With the decrease in number of runners, the hot spot moves down towards the casting, and the shrinkage and porosity defects are formed in the casting below the riser. In the original designs, a certain tendency of shrinkage and porosity defect is found in the vanes, inner rings, and outer rings of the castings by both simulation prediction and experiment. Finally, based on the processing optimization, the aero-engine turbine nozzle casting with no shrinkage and porosity defects is obtained.

Preparation of Ceramic Foam Filters With a Lithium-Containing Surface

Hydrogen in aluminum causes the formation of detrimental hydrogen porosity in castings. In order to reduce the formation of hydrogen pores, an approach was targeted using lithium as target for hydrogen. This approach utilizes the affinity of lithium for hydrogen, whereby spodumene (a lithium aluminum silicate) and lithium aluminate were used as lithium providers. Within the scope of this study, the preparation of ceramic foam filters with a coating of lithium-containing raw materials (spodumene) was investigated. Those investigations revealed that the spodumene coating has a detrimental influence on the bending strength of the foams when a certain level of spodumene is exceeded. This observation might be explainable by the intrusion of the spodumene into the alumina matrix of the skeleton foam. Two wetting tests at different temperatures were conducted, verifying the significant influence of the temperature on the reaction between the spodumene and AlSi7Mg. Furthermore, test filters coated with raw materials exhibiting different amounts of lithium were conducted. The hydrogen pores were evaluated by light microscopy and computed tomography. The analyzed pore size distribution in the aluminum did not elucidate the proximate influence of the lithium-coating on the ceramic foam filter on the hydrogen porosity in the aluminum.

Using Micro-CT Scanning to Quantitative Characterize Porosity in High Pressure Die Castings and Semi-Solid Castings

Porosity is one of the main defects that limits the performance of castings. Porosity in aluminum castings can originate from several sources, including the volumetric shrinkage occurring during solidification, the precipitation of dissolved hydrogen, and entrapment of gasses such as air, boiling water, vaporized lubricants, etc. Traditional methods of identifying and measuring porosity in castings include 2D x-rays, sectioning and polishing, and Archimedes density measurements, but none of these provide a satisfactory quantitative estimate of the size, total volume and distribution of the pores. X-ray CT scanning is a relatively new method that generates not only a 3-dimensional view of the size and distribution of the pores, but can also provide quantitative information of the volume, surface area, size, shape and position of each pore within a casting. Micro-CT scanning is a specialized sub-category of CT scanning, which provides excellent resolution of fine porosity (a resolution limit of 4 microns in one of the case-stores presented in this paper), but it should be noted that the resolution limit in CT scanning techniques is related to sample size. This paper describes results from micro-CT scanning studies of two high pressure die castings and a semi-solid casting, and provides quantitative data on the total porosity content, and the porosity distribution. The paper will also demonstrate the capabilities of the micro-CT scanning process to provide a quantitative comparison of the porosity content in these different types of aluminum castings.

Application of <i>Niyama</i> criterion to predict shrinkage porosity in vertical centrifugal casting of ASTM A356 alloy

Application of <i>Niyama</i> criterion to predict shrinkage porosity in vertical centrifugal casting of ASTM A356 alloy