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Interactive effects of grain refinement, eutectic modification and solidification rate on tensile properties of Al-10Si alloy
Jönköping University, School of Engineering, JTH, Materials and Manufacturing.ORCID iD: 0000-0002-0458-3456
Jönköping University, School of Engineering, JTH, Materials and Manufacturing.ORCID iD: 0000-0002-7527-719X
Jönköping University, School of Engineering, JTH, Materials and Manufacturing.ORCID iD: 0000-0001-5753-4052
Jönköping University, School of Engineering, JTH, Materials and Manufacturing.ORCID iD: 0000-0001-6481-5530
2017 (English)In: Journal of materials processing & manufacturing science (Print), ISSN 1062-0656, E-ISSN 1530-8065, Vol. 703, 270-279 p.Article in journal (Refereed) Published
Abstract [en]

This study aims to clarify the effect of grain size and Si modification on the microstructure and tensile properties of the Al-10Si cast alloy, solidified under various cooling rates. To replicate the effect of cooling rate, directionally solidified samples were produced by remelting of the as-cast cylindrical bars. Tensile properties, grain sizes, Si modification level and chemical composition profiles were evaluated. Results showed that fast cooling rates alone, without the addition of grain refiners (Al-5Ti-1B master alloy), did not lead to equiaxed grain morphologies. On the other hand, for the slowest cooling rate tested, combined additions of the Al-5Ti-1B and the Al-10Sr master alloys resulted in equiaxed grain structures while addition of only grain refiner resulted in columnar grains. The combined additions effectively produced an equiaxed grain structure at all cooling rates tested, and further improved the tensile properties.

Place, publisher, year, edition, pages
Elsevier, 2017. Vol. 703, 270-279 p.
Keyword [en]
Directional solidification, Grain size, EBSD, Microstructure, Aluminium alloys, Casting
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:hj:diva-36814DOI: 10.1016/j.msea.2017.07.074ISI: 000412034600031Scopus ID: 2-s2.0-85026242378OAI: oai:DiVA.org:hj-36814DiVA: diva2:1130333
Available from: 2017-08-09 Created: 2017-08-09 Last updated: 2017-12-20Bibliographically approved
In thesis
1. High performing cast aluminium-silicon alloys
Open this publication in new window or tab >>High performing cast aluminium-silicon alloys
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The need to produce lighter components due to environmental aspects and the development of electrical vehicles represents an opportunity for cast aluminium-silicon alloys. With high specific strength, good castability, high corrosion resistance and recyclability, these alloys offer an attractive combination of properties as an alternative to steel, cast iron and titanium-based components in certain applications. To take advantage of such a combination of properties, there is a need to ensure that they can be reliably achieved. In other words, high performing components need to be produced. For that, the production cycle, from alloy selection and melt preparation, to the casting and heat treatment of the component must be understood and controlled as a whole. The different steps in the production cycle will affect the microstructure of the components and hence the resulting mechanical properties. Understanding the relation between the different steps in the production cycle, its consequences on the microstructural features and on the mechanical properties constitutes the aim of this thesis.

Experiments applying state-of-the-art knowledge regarding effect of casting process, alloying system and post-process variables were performed aimed at achieving properties similar to those of high pressure die casting (HPDC) components. Different melt quality determination tools were evaluated on three different EN AC-46000 melt qualities. The influence of modification, grain refinement and both treatments together was assessed on an Al-10Si alloy solidified under different cooling rates. The tensile behaviour and the impact of features such as secondary dendrite arm spacing (SDAS) or grain sizes was quantified.

It was corroborated that by appropriate selection and control of such alloying system, process and post-process variables it is possible to achieve HPDC EN AC-46000 tensile and fatigue properties through a T5 treated sand cast EN AC-42100 alloy. On the other hand, the available techniques for melt quality assessment are inadequate, requiring further analysis to successfully identify the melt quality. Additionally, it was observed that decreasing the melt quality by additions of 25 wt.% of machining chips did not significantly decrease the tensile properties but slightly increased the variation in them. In relation to the modification and grain refinement of Al-10Si alloys it was concluded that with the slowest cooling rate tested, additions of only grain refiner did not successfully produce equiaxed grains. For cooling rates corresponding to dendrite arm spacings of 15 μm and slower, combined additions of grain refiner and modifier can lead to higher tensile properties compared to the corresponding separate additions. SDAS was observed to describe flow stress through the Hall-Petch equation but grain size did not show a physically meaningful relationship. Furthermore, beginning of cracking was detected in the plastic deformation region at dendrite/eutectic boundaries and propagated in a trans-granular fashion.

Place, publisher, year, edition, pages
Jönköping: Jönköping University, School of Engineering, 2017. 44 p.
Series
JTH Dissertation Series, 33
Keyword
Aluminium cast alloys, melt quality, eutectic modification, grain refinement, microstructure, tensile properties
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-38005 (URN)978-91-87289-34-7 (ISBN)
Presentation
2017-12-14, E1405 (Gjuterisalen), Jönköping University, School of Engineering, Jönköping, 10:00 (English)
Opponent
Supervisors
Available from: 2017-11-28 Created: 2017-11-28 Last updated: 2017-11-28Bibliographically approved

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Riestra, MartinGhassemali, EhsanBogdanoff, ToniSeifeddine, Salem

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