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    Characterization of the Effect of Melt Treatments on Melt Quality in Al-7wt %Si-Mg Alloys
    (Mdpi Ag, 2017) Uludağ, Muhammet; Cetin, Remzi; Dispinar, Derya; Tiryakioglu, Murat
    The effects of degassing, holding time and melt additions (Sr, Sr + Ti, Ti, B and B + Sr) on the quality of A356 melts were examined. A total of 120 reduced pressure test samples were collected. Pores in these samples were analyzed via digital image processing to determine the number density of pores as well as the statistical distribution of their sizes. Results showed that in all cases, degassing with argon reduced the number of defects regardless of the additions made to the melts. Moreover, all additions were found to degrade melt quality. The lowest number density of pores in all melts was achieved in melts with no additions that were degassed. In both degassed and non-degassed melts, Sr additions degraded the melt quality significantly. The mechanisms of melt quality improvement or degradation with different melt treatments are discussed in the paper.
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    EFFECT OF DEGASSING AND GRAIN REFINEMENT ON HOT TEARING TENDENCY IN Al8Si3Cu ALLOY
    (Springer International Publishing Ag, 2018) Uludağ, Muhammet; Cetin, Remzi; Dispinar, Derya; Tiryakioglu, Murat
    The effect of melt quality on hot tearing susceptibility of Al8Si3Cu alloy was examined under six different conditions, by using a traditional T-shaped mold. Grain refinement was carried out by two different modifiers: AlTi5B1 and Al3B. For each test, samples were cast before and after degassing of melt. Therefore, a new hot tearing tendency index was developed by both bifilm calculations and porosity that occurred in the middle of T-zone of casting parts. Results indicated that hot tearing of cast aluminum alloys was a complex phenomenon, and bifilms play a major role, especially by compensating for shrinkage and consequently contributing to the inconsistencies in results.
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    The effects of degassing, grain refinement & Sr-addition on melt quality-hot tear sensitivity relationships in cast A380 aluminum alloy
    (Pergamon-Elsevier Science Ltd, 2018) Uludağ, Muhammet; Cetin, Remzi; Dispinar, Derya; Tiryakioglu, Murat
    Hot tearing tendency of A380 with various element additions (Sr, Sr + Ti, Ti, B and B + Sr) was investigated. Constrained rod casting (CRC) hot tearing test method was used to characterize the hot tearing sensitivity. Reduced pressure test (RPT) samples were produced from each condition and all trials were repeated three times. Number density of pores on the cross section of RPT samples was calculated via digital image processing and statistical analysis was carried out. Microstructure analysis was carried out to observe the effect of alloying elements. Hot torn cross sections were subjected to SEM analysis. It was found that in aluminum alloys, the most deleterious defects, bifilms that are the cause of many defects, play an important role in initiating the hot tearing during solidification. It is important to note that the shape, size and distribution of bifilms are too complex. They act as heterogeneous nucleation site for liquid to separate and thus increase hot tearing.
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    ON THE INTERPRETATION OF MELT QUALITY ASSESSMENT OF A356 ALUMINUM ALLOY BY THE REDUCED PRESSURE TEST: THE BIFILM INDEX AND ITS PHYSICAL MEANING
    (Springer International Publishing Ag, 2018) Uludağ, Muhammet; Cetin, Remzi; Dispinar, Derya; Tiryakioglu, Murat
    The oxide layer on liquid aluminum serves as a protective property to prevent the alloy from further oxidation. However, it has the potential to be a source of porosity when entrained into the bulk of the liquid. For this reason, oxides entrained into aluminum castings have been shown to degrade casting quality. In the current study, the effectiveness of the reduced pressure test in assessing the quality of A356 alloy melts has been investigated under various conditions obtained by changing six different melt parameters. Several metrics, including average pore size, number density of pores, bifilm index, have been used to measure melt quality. Results have shown that the bifilm index provides reliable measurements of melt quality. Moreover, the bifilm index has been found to have a physical meaning, volume fraction of pores, especially when bifilm index is higher than 50 mm.