Research of primary Si segregation and abrasive performance of A390 hypereutectic Al-Si alloy
Date Issued
2015
Date
2015
Author(s)
Chen, Chieh-An
Abstract
While casting the A390 hypereutectic alloy, primary Si particles tend to float to the upper part of the casting due to the difference in specific weight between primary Si particles and the aluminum bulk liquid, the so-called gravity segregation. As a result, the mechanical properties in different parts of the casting vary. This research takes the advantage of the above-mentioned phenomenon of the primary silicon gravity segregation, and to enhance this segregation nature by employing centrifuging casting process to achieve better wear resistance in specific area of the castings. A centrifuging casting apparatus was constructed which allows the casting to be solidified under the centrifugal force. Under the centrifuging casting condition, the primary Si particles tend to move toward the rotational axis and aggregate at the inner portion of the castings. The experimental results indicate that the degree of primary silicon segregation toward the inner portion of the casting increases with increasing rotational speed, and reaches a plateau at 150 rpm. On the other hand, the P refinement (for primary Si) and Sr modification (for eutectic Si) of A390 alloy were performed to examine the effects of either P refinement or Sr modification on the microstructures of the centrifuging castings at 150 rpm. Further, the relationship between the microstructure features obtained and wear resistance property was evaluated. The results indicate that the inner section of the A390+0.02%Sr centrifuging casting exhibits the best wear resistance performance, which is 51% better in wear rate while compared with the A390 centrifuging castings without any treatments. In addition, segregation analysis were performed and the findings conclude that the higher the % primary Si, the lower the % porosity, the smaller the primary Si particles size, and the higher the modification degree (form class 2 to class 5), the better the wear resistance property of the A390 alloy.
Subjects
Centrifuging casting
Primary Si segregation
Refinement
Eutectic Si modification
Wear resistance property
Type
thesis
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