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Elemental Distribution, Morphological Analysis, and Hardness Measurement of an Al-Si Alloy, as Affected by Cooling Rate
Linköping University, Department of Management and Engineering. Linköping University, The Institute of Technology.
Linköping University, Department of Management and Engineering. Linköping University, The Institute of Technology.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The effects of cooling rate on the as-cast microstructure and hardness of an Al - Si alloy was studied. To obtain different cooling rates, a special gradient casting furnace was designed and built. The microstructural analysis was carried out on as-cast samples to investigate the morphology (size, shape, and distribution) of the present phases. By using an analytical scanning electron microscope, the microsegregation of different alloying elements in the centre of aluminium dendrites was investigated. To study the effect of cooling rate on the mechanical properties, hardness of the samples and microhardness of the primary α-Al dendrites were measured. The results showed that the morphology of the silicon eutectic, refinement of the intermetallics, and the size of primary dendrites are cooling rate dependent. Moreover, a clear correlation between the concentration of silicon concentration in the centre of the aluminium dendrites and cooling rate was found.

Keyword [en]
Elemental distribution, morphological analysis, hardness, Al-Si alloy
National Category
Engineering and Technology
URN: urn:nbn:se:liu:diva-70097OAI: diva2:435495
Available from: 2011-08-18 Created: 2011-08-18 Last updated: 2011-08-19Bibliographically approved
In thesis
1. On the Residual Stresses and Microstructure Formation of Aluminum-Silicon Cast Alloys
Open this publication in new window or tab >>On the Residual Stresses and Microstructure Formation of Aluminum-Silicon Cast Alloys
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Cast aluminum-silicon alloys are being increasingly used in automotive and aerospace industries for critical structure applications because of their excellent castability, low density, acceptable mechanical properties and low cost. Different casting and heat treatment parameters largely affect the microstructure and residual stress of the components, which in turn, has a great impact on their mechanical properties. In cast components, residual stresses are those stresses which may remain in the casting after it has been removed from the mould. The magnitude and distribution of the residual stresses can be critical to performance and should be considered in the design of a component. This work has been devoted to study the microstructure formation, residual stresses, and mechanical properties of aluminum-silicon castings.

The effects of casting parameters on the microstructure of the selected alloys were investigated by means of optical and scanning electron microscopes. With the help of EDS, WDS, EBSD, and quantitative analysis techniques, it was found that solidification rate, modification, superheat, casting temperature can significantly affect the nucleation and growth, morphology and chemical composition of different phases. Based on the performed microsegregation analysis, a clear correlation between the concentration of silicon in the primary phase and cooling rate was found.

Tensile tests at room and elevated temperatures in addition to microhardness experiments were performed to analyse the behaviour of the alloys under mechanical loads. The results showed that elongation to fracture, modulus of elasticity, and ultimate tensile strength of the tested alloys are temperature dependent. Moreover, the obtained information was used to establish a good model for simulating the behaviour of the cast alloys, as well as the mechanical properties and residual stresses.

The type and magnitude of residual stresses were mainly evaluated by strain gauge, sectioning, thermal analysis methods, and was also simulated by finite element analysis using Abaqus software. It was found that casting parameters such as superheat, mould hardness, casting temperature, modification, and the casting geometry, can influence the accumulated residual stress in the component. The thermal treatment experiments also indicated that the base temperature of the cast part before fast cooling, maximum temperature difference within the component, and cooling water flow can influence the residual stress. Extensive simulation work done by Abaqus showed that the results obtained by simulation are in a reasonable relationship with the experimental measurements, considering the linearly elastic/linearly isotropically hardening plastic model.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2011. 48 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1369
Al-Si alloys, residual stresses, microstructure, microsegregation, nucleation behavior, modeling
National Category
Engineering and Technology
urn:nbn:se:liu:diva-70117 (URN)978-91-7393-176-2 (ISBN)
Public defence
2011-09-07, A35, A-huset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Available from: 2011-08-19 Created: 2011-08-19 Last updated: 2012-01-19Bibliographically approved

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Sadrossadat, MohsenJohansson, Sten
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