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Influence of grain refinement on slurry formation and surface segregation in semi-solid Al-7Si-0.3Mg castings
Jönköping University, School of Engineering, JTH, Materials and Manufacturing.ORCID iD: 0000-0003-0260-5153
Department of Applied Sciences, Aalen University, Aalen, Germany.
Jönköping University, School of Engineering, JTH, Materials and Manufacturing.ORCID iD: 0000-0002-0101-0062
Jönköping University, School of Engineering, JTH, Materials and Manufacturing.ORCID iD: 0000-0002-3184-7592
2018 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 49A, no 10, p. 4871-4883Article in journal (Refereed) Published
Abstract [en]

This study aims to evaluate the effect of grain refinement on slurry formation and surface segregation in semi-solid castings produced by the Rheometal™ process. The effect of two grain refiners, Al-8B and Al-5Ti-1B, on the slurry α-Al grain size, shape factor and solid fraction was evaluated. The results suggest that the addition of a grain refiner can affect the solid fraction obtained in the RheometalTM process and, consequently, reduce the solute content near the casting surface. Grain refiner addition resulted in a larger fraction of α-Al grains ≤ 60 µm for the refined alloys compared with the unrefined alloy. Additionally, the growth of α-Al slurry globules was greater for the unrefined alloy compared with the refined alloy during solidification in the die-cavity. A more homogeneous and finer microstructure was observed near the surface in the grain-refined castings compared with the unrefined castings. Evidence of significant liquid penetration was identified in some α-Al globules, indicating that disintegration of α-Al globules may occur during the Rheometal™ casting process.

Place, publisher, year, edition, pages
Springer, 2018. Vol. 49A, no 10, p. 4871-4883
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:hj:diva-38689DOI: 10.1007/s11661-018-4787-9ISI: 000443469700048Scopus ID: 2-s2.0-85049646113Local ID: JTHMaterialISOAI: oai:DiVA.org:hj-38689DiVA, id: diva2:1178544
Note

Included in thesis in manuscript form with title: Influence of grain refinement on slurry formation and surface segregation in Al‐7Si‐0.3Mg semi‐solid castings

Available from: 2018-01-30 Created: 2018-01-30 Last updated: 2018-09-13Bibliographically approved
In thesis
1. Al-7Si-Mg semi-solid castings – microstructure and mechanical properties
Open this publication in new window or tab >>Al-7Si-Mg semi-solid castings – microstructure and mechanical properties
2018 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The vehicles industry is facing increasing demands for fuel efficiency and cost reduction due to environmental legislation, sustainability and customer demands. Therefore, there is a great need to develop and produce lightweight components by using materials and processes that offer higher specific strength and/or design optimization. Semi‐solid aluminium casting offers design freedom and castings with lower shrinkage and gas entrapment defects compared to high pressure die castings. The lack of understanding of microstructure and defect formation, and design data, for semi‐solid castings is a barrier for foundries and designers in the vehicles industry to use semi‐solid castings.

In this study, the effect of two grain refiners on slurry formation and surface segregation of semi‐solid Al‐7Si‐0.3Mg castings produced by the Rheometal™ process was evaluated. The influence of grain refinement on primary α‐Al grain size, shape factor and solid fraction was analysed in addition to the solute content of the surface segregation layer.

The influence of magnesium on the formation of intermetallic phases during solidification and the heat treatment response of Al‐7Si‐Mg semi‐solid castings was investigated. The magnesium content was varied from 0.3 to 0.6wt.% and the semi-solid castings were analysed in the T5 and T6 conditions. Energy dispersive spectroscopy was used to identify the intermetallic phases formed during solidification. Tensile testing was performed and the results were correlated to the magnesium and silicon concentration measured in the interior of the α‐Al globules formed during slurry preparation.

The results suggest that the addition of grain refiner decreases the solid fraction obtained in the Rheometal™ process. However, no significant effect was observed on the α‐Al grain size and shape factor.

A good correlation was obtained between the magnesium concentration in the interior of the α‐Al globules formed during slurry preparation and the offset yield strength for all alloys. The low magnesium solubility in α‐Al at temperatures in the solidification range of the Al‐7Si‐Mg alloys is suggested to be the reason for the low hardening response for the T5 heat treatment compared to the T6 condition.

Place, publisher, year, edition, pages
Jönköping: Jönköping University, School of Engineering, 2018. p. 43
Series
JTH Dissertation Series ; 036
Keywords
Rheometal™ process; semi‐solid casting; aluminium alloys; grain refinement; segregation; intermetallic phases; heat treatment; mechanical properties
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-38693 (URN)978-91-87289-37-8 (ISBN)
Supervisors
Available from: 2018-01-30 Created: 2018-01-30 Last updated: 2018-08-16Bibliographically approved

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Santos, JorgeJarfors, Anders E.W.Dahle, Arne

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