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On solidification of hypereutectic Al-Si alloys
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
2009 (English)In: Transactions of the Indian Institute of Metals, ISSN 0019-493X, Vol. 62, no 4-5, 361-365 p.Article in journal (Refereed) Published
Abstract [en]

Precipitation of primary silicon was studied in Al-Si hypereutectic alloys with 15, 18, and 25 wt. % silicon content. The alloys were solidified with different cooling rates from different super heat temperatures. The liquidus and eutectic temperature were evaluated from the cooling curves. The liquidus temperature was found to decrease with cooling rate. The evaluation of microstructure showed that the fraction of primary silicon decreased with increasing the cooling rate and super heat temperature. Furthermore, the morphology of the primary silicon changed as an effect of cooling rate and super heat temperature.

Place, publisher, year, edition, pages
2009. Vol. 62, no 4-5, 361-365 p.
Keyword [en]
hypereutectic Al-Si alloy, solidification, bcooling rate, super heat
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-14203ISI: 000276133700022Scopus ID: 2-s2.0-76249083519OAI: oai:DiVA.org:kth-14203DiVA: diva2:331749
Note
QC 20100726Available from: 2010-07-26 Created: 2010-07-26 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Volume Change Effects during Solidification of Alloys
Open this publication in new window or tab >>Volume Change Effects during Solidification of Alloys
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Volume change during solidification is an important concept in achieving of casting soundness. The solidification shrinkage can cause different defects in the ingot casting as well as the shape casting. The volume change due to phase transformation during solidification is the other concept which has to be studied. In addition, the solidification shrinkage can be affected by the volume change of liquid metals due to the structure change of liquid.

In this work, first, the solidification shrinkage was measured in copper-lead base alloys by a dilatometer which was developed to use for melting and solidification processes. The volume change was measured during primary solidification and monotectic reaction. The macrostructure evaluation of samples was used to explain the volume change results. A shrinkage model was used to explain the volume changes during solidification. In addition, the microsegregation of alloying elements was studied in the alloys.

 

In the second part, the solidification of brass alloys was investigated in different cooling rates. Microstructure evaluation showed that the peritectic transformation occurred as diffusionless (partitionless) as well as the diffusion-controlled transformation. In addition, the volume change was measured in the peritectic alloys. A theoretical analysis was developed to evaluate the volume change effect on the peritectic reaction.

 

Hot crack formation was investigated during the solidification of peritectic steels as a volume change concept during the transformation of ferrite to austenite. A series of in situ solidification experiments was performed using a MTS tensile testing machine combined with a mirror furnace to measure the sample temperature and the force change during solidification. It was observed that a rise in tensile force began with the start of solidification and suddenly dropped. The sudden drop of force, which occurred around the peritectic temperature of the alloy, was accompanied by a crack or a refilled crack in the microstructure. Furthermore, the peritectic reaction types were studied theoretically and experimentally to understand their effects on the force change during solidification. The analyses showed that the volume change due to the peritectic transformation is a reason for crack formation. In addition, when the peritectic reaction occurred as a diffusionless manner (partitionless), the crack formation is more probable.

 

In the last study, the effect of cooling rate and super heat temperature were studied on the precipitation of primary silicon in Al-Si hypereutectic alloys. The liquidus temperature was found to decrease with cooling rate. In addition, the fraction of primary silicon decreased with increasing the cooling rate and the super heat temperature. Furthermore, the morphology of the primary silicon changed as an effect of cooling rate and super heat temperature. It was concluded that the solidification characteristic and silicon morphology relate to the liquid structure.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2009. xii, 46 p.
Series
Trita-MG, ISSN 1104-7127 ; 2009:3
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-10527 (URN)978-91-7415-351-4 (ISBN)
Public defence
2009-06-12, F3, Lindstedtsvägen 26, KTH, 13:00 (English)
Opponent
Supervisors
Note
QC 20100726Available from: 2009-06-04 Created: 2009-05-25 Last updated: 2011-03-21Bibliographically approved

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