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Abstract

Porosity is one of the major problems in casting operations and there are several discussions in the literature about the porosity formation in aluminum castings. Bifilms are the defects that are introduced into the melt by turbulence. They can be detected with reduced pressure test and presented numerically by measuring bifilm index. The measure of bifilm index is the sum of total oxide length given in millimeters from the cross-section of reduced pressure test sample solidified under 0.01 MPa. In this work, low pressure die casting (LPDC) unit was built in an attempt to enhance the producibility rate. The unit consists of a pump housing that was placed inside the melt in the melting furnace where the pressure was applied instead of the whole melt surface. It was observed that the melt quality of A356 alloy was deteriorated over time which had led to higher porosity. This was attributed to the increased oxide thickness of the bifilm by the consumption of air in between the folded oxides. A relationship was found between bifilm index and pore formation.
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Bibliography

[1] Campbell, J. (2011). Complete Casting Handbook: Metal Casting Processes. Techniques and Design. Elsevier Science.
[2] Bonollo, F., Urban, J., Bonatto, B. & Botter, M. (2005). Gravity and low pressure die casting of aluminium alloys: a technical and economical benchmark. La Metallurgia Italiana. 6, 23-32.
[3] Dispinar, D. & J. Campbell, (2004). Critical assessment of reduced pressure test. Part 2: Quantification. International Journal of Cast Metals Research. 17(5), 287-294.
[4] Raiszadeh, R., & Griffiths, W.D. (2006). A method to study the history of a double oxide film defect in liquid aluminum alloys. Metallurgical and Materials Transactions B. 37(6), 865-871.
[5] Raiszadeh, R., & Griffiths, W.D. (2008). A semi-empirical mathematical model to estimate the duration of the atmosphere within a double oxide film defect in pure aluminum alloy. Metallurgical and Materials Transactions B. 39(2), 298-303.
[6] Raiszadeh, R., & Griffiths, W.D. (2011). The effect of holding liquid aluminum alloys on oxide film content. Metallurgical and Materials Transactions B. 42(1), 133-143.
[7] Aryafar, M., Raiszadeh, R., & Shalbafzadeh, A. (2010). Healing of double oxide film defects in A356 aluminium melt. Journal of materials science. 45(11), 3041-3051.
[8] Farhoodi, B., Raiszadeh, R., & Ghanaatian, M. H. (2014). Role of double oxide film defects in the formation of gas porosity in commercial purity and Sr-containing Al alloys. Journal of Materials Science & Technology. 30(2), 154-162.
[9] Amirinejhad, S., Raiszadeh, R., & Doostmohammadi, H. (2013). Study of double oxide film defect behaviour in liquid Al–Mg alloys. International Journal of Cast Metals Research. 26(6), 330-338.
[10] Bakhtiarani, F.N., & Raiszadeh, R. (2011). Healing of double-oxide film defects in commercial purity aluminum melt. Metallurgical and Materials Transactions B. 42(2), 331-340.
[11] Bagherpour-Torghabeh, H., Raiszadeh, R., & Doostmohammadi, H. (2017). Role of Mechanical Stirring of Al-Mg Melt in the Healing of Bifilm Defect. Metallurgical and Materials Transactions B. 48(6), 3174-3184.
[12] Nateghian, M., Raiszadeh, R., & Doostmohammadi, H. (2012). Behavior of Double-Oxide Film Defects in Al-0.05 wt pct Sr Alloy. Metallurgical and Materials Transactions B. 43(6), 1540-1549.
[13] Stefanescu, D.M. (2005). Computer simulation of shrinkage related defects in metal castings - a review. International Journal of Cast Metals Research. 18, 129-143.
[14] Zhu, J.D., Cockcroft, S.L., Maijer, D.M. & Ding, R. (2005). Simulation of microporosity in A356 aluminium alloy castings. International Journal of Cast Metals Research. 18, 229-235.
[15] Merlin, M., Timelli, G., Bonollo, F. & Garagnani, G.L. (2009). Impact behaviour of A356 alloy for low-pressure die casting automotive wheels. Journal of Materials Processing Technology. 209(2), 1060-1073.
[16] Zhang, B., Maijer, D.M. & Cockcroft, S.L. (2007). Development of a 3-D thermal model of the low-pressure die-cast (LPDC) process of A356 aluminum alloy wheels. Materials Science and Engineering: A, 464(1-2), 295-305.
[17] Zhang, B., Cockcroft, S.L., Maijer, D.M., Zhu, J.D. & Phillion, A.B. Casting defects in low-pressure die-cast aluminum alloy wheels. JOM Journal of the Minerals, Metals and Materials Society, 57(11), 36-43.
[18] Campbell, J. (1968). Hydrostatic tensions in solidifying materials. Transactions of the Metallurgical Society of AIME, 242 (February), 264-267.
[19] Campbell, J. (1968). Hydrostatic tensions in solidifying alloys. Transactions of the Metallurgical Society of AIME, 242 (February), 268-271.
[20] Campbell, J. (1967), Shrinkage pressure in castings (The solidification of a Metal Sphere). Transactions of the Metallurgical Society of AIME, 239 (February), 138-142.
[21] Dispinar, D. & Campbell, J. (2004). Critical assessment of reduced pressure test. Part 1: Porosity phenomena. International Journal of Cast Metals Research. 17(5), 280-286.
[22] Dispinar, D., Akhtar, S., Nordmark, A., Di Sabatino, M., & Arnberg, L. (2010). Degassing, hydrogen and porosity phenomena in A356. Materials Science and Engineering: A. 527(16-17), 3719-3725.
[23] Puga, H., Barbosa, J., Azevedo, T., Ribeiro, S. & Alves, J.L. (2016). Low pressure sand casting of ultrasonically degassed AlSi7Mg0. 3 alloy: Modelling and experimental validation of mould filling. Materials & Design. 94, 384-391.
[24] El-Sayed, M.A. & Essa, K. (2018). Effect of mould type and solidification time on bifilm defects and mechanical properties of Al–7si–0.3 mg alloy castings. Computational and Experimental Studies, 23.
[25] Gyarmati, G., Fegyverneki, G., Mende, T. & Tokár, M. (2019). Characterization of the double oxide film content of liquid aluminum alloys by computed tomography. Materials Characterization. 157, 109925. [26] Gyarmati, G., Fegyverneki, G., Tokár, M., & Mende, T. (2020). The Effects of Rotary Degassing Treatments on the Melt Quality of an Al–Si Casting Alloy. International Journal of Metalcasting. 1-11.
[27] Tiryakioğlu, M. (2020). The Effect of Hydrogen on Pore Formation in Aluminum Alloy Castings: Myth Versus Reality. Metals. 10(3), 368.
[28] Tiryakioğlu, M. (2019). Solubility of hydrogen in liquid aluminium: reanalysis of available data. International Journal of Cast Metals Research. 32(5-6), 315-318.
[29] Tiryakioğlu, M. (2020). A simple model to estimate hydrogen solubility in liquid aluminium alloys. International Journal of Cast Metals Research. 1-3.
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Authors and Affiliations

O. Gursoy
1
A. Nordmak
2
F. Syvertsen
2
M. Colak
3
K. Tur
4
D. Dispinar
5
ORCID: ORCID

  1. University of Padova, Italy
  2. SINTEF, Norway
  3. University of Bayburt, Turkey
  4. Atilim University, Turkey
  5. Istanbul Technical University, Turkey
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Abstract

In this work, 25 wheels were cast with three different grain refiners: Al5Ti1B, Al3Nb1B and MTS 1582. Samples were machined from the wheels to check the mechanical properties. It was found that Nb grain refinement had the lowest grain size (260 mm) and highest tensile properties (yield strength of 119-124 MPa and ultimate tensile strength of 190-209 MPa). Al5Ti1B and MTS 1582 revealed quite similar results (110 MPa yield and 198 MPa ultimate tensile strength). The fading of the grain refining effect of Al5TiB1 master alloy was observed in both Nb and Ti added castings whereas during the investigated time interval, the fading was not observed when MTS 1582 was used.
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Authors and Affiliations

F. Aydogan
1
K.C. Dizdar
2
ORCID: ORCID
H. Sahin
2
ORCID: ORCID
E. Mentese
1
D. Dispinar
2
ORCID: ORCID

  1. Doktas Wheels, Turkey
  2. Istanbul Technical University, Turkey
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Abstract

Aluminum alloys are widely used in the industry thanks to its many advantages such as light weight and high strength. The use of this material in the market is increasing day by day with the developing technology. Due to the high energy inputs in the primary production, the use of secondary ingots by recycling from scrap material are more advantageous. However, the liquid metal quality is quite important in the use of secondary aluminum. It is believed that the quality of recycled aluminum is low, for this purpose, many liquid metal cleaning methods and test methods are used in the industry to assess the melt cleanliness level. In this study, it is aimed to examine the liquid metal quality in castings with varying temperature using K mold. A206 alloy was used, and the test parameters were selected as: (i) at 725 °C, 750 °C and 775 °C casting temperatures, (ii) different hydrogen levels. The hydrogen level was adjusted as low, medium and high with degassing, as-cast, and upgassing of the melt, respectively. The liquid metal quality of the cast samples was examined by the K mold technique. When the results were examined, it was determined that metal K values and the number of inclusions were high at the as-cast and up-gas liquid with increasing casting temperatures. It has been understood that the K mold technique is a practical method for the determination of liquid metal quality, if there is no reduced pressure test machine available at the foundry floor.
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Authors and Affiliations

A. Tigli
1 2
ORCID: ORCID
M. Tokatli
3
E. Uslu
3
ORCID: ORCID
M. Colak
3
D. Dispinar
1 4
ORCID: ORCID

  1. Istanbul Technical University, Turkey
  2. Sinop University, Turkey
  3. Bayburt University, Turkey
  4. Foseco, Netherlands
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Abstract

Aluminum and its alloys are one of the most favored metal-based materials for engineering applications that require lightweight materials. On the other hand, composites are getting more preferable for different kinds of applications recently. Boron nitride nanotubes (BNNTs) are one of the excellent reinforcement materials for aluminum and its alloys. To enhance mechanical properties of aluminum, BNNTs can be added with different processes. BNNT reinforced aluminum matrix composites also demonstrate extraordinary radiation shielding properties. This study consists of BNNT reinforced aluminum matrix composite production performed by casting method. Since wetting of BNNT in liquid aluminum is an obstacle for casting, various casting techniques were performed to distribute homogeneously in liquid aluminum. Different methods were investigated in an aim to incorporate BNNT into liquid method as reinforcement. It was found that UTS was increased by 20% and elongation at fracture was increased by 170% when BNNT was preheated at 800°C for 30 minutes.
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Authors and Affiliations

B. Nemutlu
1
ORCID: ORCID
O. Kahraman
1
ORCID: ORCID
K. B. Demirel
1
ORCID: ORCID
I. Erkul
1
ORCID: ORCID
M. Cicek
1
ORCID: ORCID
H. Sahin
1
ORCID: ORCID
K.C. Dizdar
1
ORCID: ORCID
D. Dispinar
1
ORCID: ORCID

  1. Istanbul Technical University, Turkey

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