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The effects of solidification conditions and heat treatment on the microstructure and mechanical properties of EN-AC 44400 alloy
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
2010 (English)In: Materials Science Forum, ISSN 0255-5476, Vol. 649, 505-510 p.Article in journal (Refereed) Published
Abstract [en]

Improved mechanical and physical properties of an Al-Si alloy as a well-known casting alloy is strongly dependent upon the morphology of silicon particles, Al grains and also type of intermetallics which are in turn a function of alloy composition, solidification rate and heat treatment. This study aims at investigating the influence of the different solidification conditions (high pressure die, gradient and sand cast) and heat treatment on the microstructure (dendrite parameters, silicon particle morphology, intermetallic compounds), mechanical properties and fracture surface appearance of Al- 9Si- 4Mn alloy. To identify the features of microstructure and fracture surface analysis, a combination of optical metallography, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) have been employed. The results show that the cooling rate has a strong effect on the evolution of intermetallics, morphology of the silicon and dendrite parameters.

Place, publisher, year, edition, pages
Switzerland: Trans Tech Publications , 2010. Vol. 649, 505-510 p.
Keyword [en]
solidfication conditions, microstructure, mechanical properties, intermetallics, heat treatment
National Category
Engineering and Technology
URN: urn:nbn:se:liu:diva-54536DOI: 10.4028/ diva2:305141
Available from: 2010-03-22 Created: 2010-03-22 Last updated: 2011-08-24Bibliographically 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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