scholarly journals A Review Study on the Main Sources of Porosity in Al-Si Cast Alloys

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Agnes Samuel ◽  
Yasser Zedan ◽  
Herbert Doty ◽  
Victor Songmene ◽  
Fawzy. H. Samuel
Keyword(s):  
Fatigue Testing ◽  
Point Of View ◽  
Porosity Formation ◽  
Reduced Pressure ◽  
Nucleation Sites ◽  
Pressure Test ◽  
Cast Alloys ◽  
Review Study ◽  
Pure Metals ◽  
Shrinkage Cavities

The present study was performed on A356 and B319 alloys in mechanically stirred or degassed condition. Melts were Sr-modified and grain-refined. Hydrogen content was varied from less than 0.1 ml/100 g Al to ∼0.4 ml/100 g Al; Fe was increased to 0.8% in B319 alloy. Lanthanum and cerium were added as 99.5% pure metals. Two main techniques were used to investigate porosity formation: fracture surface of tensile or fatigue test bars, or reduced pressure test (RPT) method. Porosity type and shape were examined. The results show that pore size is more influential than small scattered ones from a mechanical point of view. Tensile testing is affected by porosity located at the center of the testing bar, whereas edge porosity is responsible for crack initiation in case of fatigue testing. Intermetallics precipitate in the form of intercepted platelets which restricts the flow of the molten metal, leading to formation of shrinkage cavities. Precipitation of clusters of compounds from the liquid state such as Al2Si2Sr, Mg2Sn, Al3Ti, or added Al2O3particles would as well act as nucleation sites for porosity formation. Most oxides were observed in the form of long branched strings. In some cases, bifilms were also reported in addition to SrO and MgO.

scholarly journals Mechanical Properties and Melt Quality Relationship of Sr-modified Al-12Si Alloy

2015 ◽  
Vol 15 (4) ◽  
pp. 134-140 ◽  
Author(s):  
M. Uludağa ◽  
M. Uyaner ◽  
F. Yilmaz ◽  
D. Dişpinar
Keyword(s):  
Mechanical Properties ◽  
Oxide Film ◽  
Tensile Testing ◽  
Porosity Formation ◽  
Reduced Pressure ◽  
Cast Part ◽  
Pressure Test ◽  
Relationship Of ◽  
Good Agreement

Abstract The formation of oxide film on the surface of aluminium melts, i.e. bifilms, are known to be detrimental when they are incorporated into the cast part. These defects causes premature fractures under stress, or aid porosity formation. In this work, Al-12 Si alloy was used to cast a step mould under two conditions: as-received and degassed. In addition, 10 ppi filters were used in the mould in order to prevent bifilm intrusion into the cast part. Reduced pressure test samples were collected for bifilm index measurements. Samples were machined into standard bars for tensile testing. It was found that there was a good agreement with the bifilm index and mechanical properties.

Stability of a Piezoresistive Ceramic Pressure Sensor Made With LTCC Technology

2012 ◽  
Vol 2012 (CICMT) ◽  
pp. 000371-000376 ◽  
Author(s):  
Marina Santo Zarnik ◽  
Darko Belavic
Keyword(s):  
Pressure Sensor ◽  
Fatigue Testing ◽  
Low Pressure ◽  
Fatigue Tests ◽  
Point Of View ◽  
Long Term Stability ◽  
Pressure Cycling ◽  
Key Characteristics ◽  
The Stability

This paper discusses the stability of a piezoresistive, LTCC-based, pressure sensor that was designed for measurements in a low-pressure range below 100 mbar. The intrinsic stability of the sensor's offset was evaluated at a constant ambient temperature and different conditions regarding the atmospheric humidity. The sensors were also subjected to functional fatigue tests, which included a full-scale and an overload pressure cycling. The results of the fatigue testing revealed the vulnerability of the sensor's structure from the point of view of the long-term stability and the life-cycle. Nevertheless, the stability of the key characteristics of the prototype sensors was found to be satisfactory for accurate measurements in the low-pressure ranges.

scholarly journals Effects of Casting Conditions for Reduced Pressure Test on Melt Quality of Al-Si Alloy

Metals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1422
Author(s):  
Ho Sung Jang ◽  
Ho Jung Kang ◽  
Jin Young Park ◽  
Yoon Suk Choi ◽  
Sunmi Shin
Keyword(s):  
Sampling Method ◽  
Hydrogen Diffusion ◽  
Heating Temperature ◽  
Reduced Pressure ◽  
Hydrogen Diffusion Coefficient ◽  
Atmospheric Exposure ◽  
Pressure Test ◽  
The Difference ◽  
The One

The present study investigated the effect of the casting conditions for the reduced pressure test (RPT) on the melt quality of Al-Si alloy. The casting conditions considered in RPT were the atmospheric exposure during melting, sampling method, and mold pre-heating temperature. Density Index (DI) was measured to quantify the melt quality of the Al-Si alloy casted with the different casting conditions for the RPT. The sample with blocking atmospheric exposure during melting was 5.6% lower in DI than the one without blocking. DI showed a 1.9% gap between scooping-out and pouring sampling methods. Increasing mold pre-heating temperature from 100 °C to 250 °C increased the DI of the alloy from 8.5% to 18.7%. On the other hand, when the mold pre-heating temperature was 350 °C, the DI of the alloy dropped sharply to 0.9%. The melt quality of the alloys was analyzed by measuring the pores and microstructure and simulating the solidification of the samples. It was presumed that the oxides and inclusions in the molten alloys caused the difference in DI according to the atmospheric exposure and the sampling method. The difference in DI according to the mold pre-heating temperature could be understood by calculating the solidification starting time and hydrogen diffusion coefficient during the solidification of the alloys in RPT.

New Steps to Improve Rotordynamic Stability Predictions of Centrifugal Compressors

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Manoj K. Gupta ◽  
Thomas A. Soulas ◽  
Dara W. Childs
Keyword(s):  
Centrifugal Compressor ◽  
Flow Model ◽  
Aerodynamic Performance ◽  
Magnetic Bearing ◽  
Point Of View ◽  
Test Results ◽  
Performance Point ◽  
Pressure Test ◽  
Full Pressure ◽  
Rotor Model

Improved rotordynamic stability is desired by end users, and centrifugal compressor manufacturers are expected to meet, if not exceed, this expectation. Compressor manufacturers are required to design and build machines that are rotordynamically stable on the test stand and in the field. Confidence has been established in predicting the excitation forces from seals and bearings, but impeller aerodynamic excitation forces continue to be a challenge. While much attention is paid to impellers from an aerodynamic performance point of view, more efforts are needed from a rotordynamic standpoint. A high-pressure, reinjection centrifugal compressor is analyzed in order to predict rotordynamic stability using the best available resources for seals and bearings. Impeller shroud forces are predicted using the bulk-flow model developed by Gupta and Childs (Gupta, M., and Childs, D., Proc. of ASME Turbo Expo 2000, Power for Land, Sea, and Air). Each impeller stage is analyzed and an attempt is made to improve the estimation of impeller aerodynamic excitation forces. Logarithmic decrement (log dec) predictions for the full rotor model consisting of all the stages and seals are compared to the full-load full-pressure test measured values using a magnetic bearing exciter. A good correlation is obtained between the measured test results and analytical predictions.

Organometallic Vapor Phase Epitaxy: Features, Problems, New Approaches

MRS Bulletin ◽  
1988 ◽  
Vol 13 (11) ◽  
pp. 37-44 ◽  
Author(s):  
Sorab K. Ghandhi ◽  
Ishwara B. Bhat
Keyword(s):  
Molecular Beam ◽  
Elevated Temperatures ◽  
Chemical Vapor ◽  
Compound Semiconductor ◽  
Point Of View ◽  
Organometallic Vapor Phase Epitaxy ◽  
High Quality ◽  
Reduced Pressure ◽  
Gaas Devices ◽  
Crystalline Substrate

Modern compound semiconductor devices are usually fabricated in one or more layers of single-crystal material, which are epitaxially grown on a crystalline substrate. Since most of these semiconductors decompose into their constituent components at high temperature, epitaxial growth in its simplest form can be accomplished by transporting individual components to a heated substrate, where they react to form the compound semiconductor. This is the basis of molecular beam epitaxy (MBE), where the process is carried out in an ultrahigh vacuum environment.Growth of these materials in an atmospheric (or reduced pressure) environment is highly advantageous from a commercial point of view. However, this presents a problem, since one of the components usually has a very low vapor pressure. For III-V compounds such as GaAs, AlAs, InAs, and InP, this is the column III component. Consequently, a technique must be provided to transport these elements by means of volatile compounds. This process is known as chemical vapor epitaxy, with halogenic compounds often used as transport agents. One example of this approach is the growth of GaAs from GaCl and AsCl3. During growth, the AsCl3 is made to prereact with gallium to form volatile GaCl, which is stable at elevated temperatures and can be transported to the substrate. High quality GaAs can be made by this process, and it is widely used for making a number of GaAs devices.

scholarly journals Melt Treatment-Porosity Formation Relationship in Al-Si Cast Alloys

2021 ◽  
Author(s):  
Dominique Gagnon ◽  
Agnes M. Samuel ◽  
Fawzy H. Samuel ◽  
Mohamed H. Abdelaziz ◽  
Herbert W. Doty
Keyword(s):  
Electron Probe ◽  
Solidification Rate ◽  
Optical Microscope ◽  
Image Analyzer ◽  
Grain Refining ◽  
Porosity Formation ◽  
Optical Microscope Image ◽  
Melt Treatment ◽  
Cast Alloys ◽  
Hydrogen Level

The present study focuses on the porosity formation in three Al-Si cast alloys widely used in automotive industries viz. A319.0, A356.0, and A413.0 alloys under various conditions: stirring, degassing. Sr level, amount of grain refining, combined modification and grain refining, as well as hydrogen level. The solidification rate was the same for all alloys in terms of the mold used and its temperature. The microstructural investigations were carried out quantitatively using an optical microscope-image analyzer system scanning systematically over a polished sample area of 25 mm × 25 mm and qualitatively using an electron probe microanalzer equipped with EDS and WDS systems. The results were coupled with hardness measurements.

Measurement and Analysis of Bubble Behavior in Subcooled Nucleate Boiling Flow Field With High Fidelity Imaging System

2004 ◽  
Author(s):  
Wen Wu ◽  
Barclay G. Jones ◽  
Ty A. Newell
Keyword(s):  
Flow Field ◽  
Power Distribution ◽  
Imaging System ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Point Of View ◽  
High Fidelity ◽  
Bubble Behavior ◽  
Reduced Pressure ◽  
Power Shift

To date, more than twenty PWRs have been affected by axial offset anomaly (AOA) or crud-induced power shift (CIPS), an unexpected deviation in the core axial power distribution from the predicted curve during operation. AOA is a current major consideration for reactors operating at increased power levels and is becoming immediate threat to nuclear power’s competitiveness in the market [1]. Despite much effort focusing on this topic, a comprehensive understanding is far from being developed. However, previous research indicates that a close connection exists between subcooled nucleate boiling occurring in core region and the formation of crud, which directly results in AOA phenomena. It is well established that deposition is greater, and sometimes much greater, on heated than on unheated surfaces. [2] A number of researchers have suggested that boiling promotes deposition, and several observed increased deposition in the subcooled boiling region [2]. Limited detailed information is available on the interaction between heat and mass transfer in subcooled nucleate boiling (SNB) flow. It is speculated that direct prediction of the AOA from SNB is difficult. Moreover, bubbles formed in SNB region play an important role in helping the formation of crud. Therefore, we are encouraged to get a better understanding of SNB phenomena and the behavior of the bubbles in SNB. This research examines bubble behavior under SNB condition from the dynamic point of view, using a high fidelity digital imaging apparatus. Freon R-134a is chosen as a simulant fluid due to its merit of having smaller surface tension and lower boiling temperature. The apparatus is operated at “reduced” pressure. Series of images at frame rates up to 4000 frames/s were obtained, showing different characteristics of bubble behavior with varying experimental parameters e.g. flow velocity, fluid subcooled level, etc. Analyses that combine the experimental results with analytical result on flow field in velocity boundary layer are considered. A tentative suggestion is that a rolling movement of a bubble accompanies its sliding along the heating surface in the flow channel. Numerical computations using FLUENT v5.5 are performed to support this conclusion.

I-3 ASSESSMENT OF REDUCED PRESSURE TEST FOR HYDORGEN MEASUREMENT OF ALUMINUM CASTING(Session: Casting/Molding)

2006 ◽  
Vol 2006 (0) ◽  
pp. 149
Author(s):  
R. Sirichaivetkul ◽  
A. Rengsomboon ◽  
W. Samit ◽  
N. Moonrin ◽  
S. Petcrie ◽  
...  
Keyword(s):  
Aluminum Casting ◽  
Reduced Pressure ◽  
Pressure Test

The Porosity Description in Hypoeutectic Al-Si Alloys

2016 ◽  
Vol 682 ◽  
pp. 83-90 ◽  
Author(s):  
Bartłomiej Dybowski ◽  
Łukasz Poloczek ◽  
Andrzej Kiełbus
Keyword(s):  
Mechanical Properties ◽  
Volume Fraction ◽  
Quantitative Description ◽  
Eutectic Mixture ◽  
Shrinkage Porosity ◽  
Aluminum Casting ◽  
Important Group ◽  
Casting Alloys ◽  
Cast Alloys ◽  
Shrinkage Cavities

Al-Si alloys are the most important group among aluminum casting alloys. They are widely used in automotive and aerospace industries. Chemical modification of the Al-Si alloys leads to formation of fine, fibrous Al-Si eutectic mixture ensuring high mechanical properties. The modification is however known to increase the alloy porosity, which may, in turn, result in decrease of its properties. The following paper presents results of the research on quantitative description of the Al-Si cast alloys porosity and influence of Na modification on the porosity of AlSi9Mg alloy. Porosity in the hypoeutectic Al-Si alloys occurs in four types: shrinkage cavities, shrinkage porosity, isolated gas pores and gas pores surrounded by shrinkage porosity. Na modification leads to increase of shrinkage pores volume fraction.

Influence of the Casting Process on the Properties of Al Based Automotive Components

2007 ◽  
Vol 23 ◽  
pp. 25-32
Author(s):  
Mario Rosso ◽  
Marco Actis Grande
Keyword(s):  
Fatigue Testing ◽  
Fatigue Cracks ◽  
Hot Isostatic Pressing ◽  
Casting Process ◽  
Fatigue Properties ◽  
Automotive Components ◽  
Nucleation Sites ◽  
Engine Blocks ◽  
Casting Sand ◽  
Mould Casting

This work concerns the study of the fatigue properties of A319, A 356 and A357 Aluminum alloys, produced by means of permament mould casting, sand casting and loast foam. Smooth plane or cylindrical samples were cut out from supension arms, engine blocks and cylinder heads and then they were subjected to axial fatigue testing at room temperature. Some castings were subjected to LHIP (Liquid Hot Isostatic Pressing) and also the effect of this process has been evaluated regarding the improvement of fatigue properties. Optical microscopy and scanning electron microscopy (SEM) were used to document the elimination of porosity after LHIP and to show the different nucleation sites of fatigue cracks on the fracture surfaces in no-LHIP and LHIP conditions.

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