The effect of melt refining upon inclusions in aluminum
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I.
INTRODUCTION
I T is well established that multistage filters like ALCOA 4691 and FILD, 2 as well as flotation units like SNIF,3 have a beneficial effect upon melt cleanliness. The main limitation in the testing of these units has been that the measurements are qualitative with respect to inclusions. Thus, we decided to use a series of methods including centrifuging of melts 4 to determine the effect of these units upon the content and size distribution of inclusions. The number of analyses is far too few to be a general test of the units, but the present paper is meant to indicate how they can be tested. The work has been concentrated upon the main types of inclusions in aluminum, 5 that is, oxides, borides, and carbides.
II.
EXPERIMENTAL P R O C E D U R E
The first group of experiments was carried out at different plants, letting aluminum melts be refined by use of ALCOA 469, FILD, and SNIF, respectively. The alloy composition of the materials investigated is summarized in Table 1. The melts were DC-cast. Samples of the original melts and the refined materials were taken at corresponding times during the refining processes. Thus, material number one refined by use of ALCOA 469 was tested when 50 pet of the volume of the melt had been cast, material number two refined in FILD after 10 pet and 65 pet had been cast, and material number three refined in SNIF, after 10 pet, 50 pet, and 90 pet had been cast.
Table 1.
During this investigation it became evident that the borides were agglomerated in SNIE Thus, we decided to test the effect of SNIF upon borides and oxides in more detail. Four melts of A1 99.7 pet were refined with SNIF, and samples were taken as described above. The sampling of the melts was performed in the following ways: 1. 100 g samples by DIPSI, an immersion chill mold. The sampling technique has been described by Aschehoug and Lauritzen.6 2. The surface oxide layer was removed, and a graphite crucible was dipped into the melt. The 0.5 to 1 kg sample of the melt was cast in the crucible. Specimens were then made of sections situated at least 1 cm from the crucible wall and the top surface. Samples were also sectioned from the cylindrical DC-ingots. The results are expressed as the means of two to four analyses at each stage. The concentration of the inclusions was measured in the following ways: 1. 100 to 120 g samples were heated to 750 to 800 ~ and subsequently centrifuged with rotation frequency of 500 to 2500 rpm until the melt froze. The content of sedimented borides was measured by means of emission spectroscopy. 4 2. 17.4 g cylindrical samples were cut with a lathe, and the oxygen content was determined by neutron activation analysis. 5 3. 0.5 g samples were dissolved in a sodium hydroxide solution, and the concentration of A14C3 was determined
Spectrographic Measurements of the Chemical Composition of the Materials Investigated.
Material Number
Refining Unit Used:
A1
Mg
Si
I* 2 3
ALCOA 469 FILD SNIF
Base Base Base
4.5 0.5 --
0.2 0.5 0.08
Alloy Composition in Wt Pet Fe Mn
Data Loading...
