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Santos, J., Jarfors, A. E. .. & Dahle, A. (2019). Formation of Iron-Rich Intermetallic Phases in Al-7Si-Mg: Influence of Cooling Rate and Strontium Modification. Metallurgical and Materials Transactions. A, 50(9), 4148-4165
Open this publication in new window or tab >>Formation of Iron-Rich Intermetallic Phases in Al-7Si-Mg: Influence of Cooling Rate and Strontium Modification
2019 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 50, no 9, p. 4148-4165Article in journal (Refereed) Published
Abstract [en]

The influence of cooling rate on the formation of iron-rich intermetallic phases during solidification of unmodified and strontium-modified Al-7Si-0.3Mg alloys has been investigated. The effect of strontium on the intermetallic phases was evaluated in unquenched and quenched samples. Samples were quenched before the start of the Al-Si eutectic reaction, along the Al-Si eutectic reaction and just after the end of solidification. The results show that the addition of strontium increased the size of both β-Al5FeSi and π-Al8FeMg3Si6 at low cooling rates. For unmodified and strontium-modified alloys, an increase of cooling rate resulted in a decrease in size of the intermetallic phases, particularly in the strontium modified alloy. In the strontium modified alloy quenched before the start of the Al-Si eutectic reaction, π-Al8FeMg3Si6 appeared as thin platelets at the eutectic cell boundaries. Chinese script-like π-Al8FeMg3Si6 and platelet-like β-Al5FeSi intermetallic phases were observed uniformly distributed in the eutectic regions in the unmodified alloy quenched before the start of the eutectic reaction. Strontium modified semi-solid Al-7Si-0.3Mg castings were produced and the type of intermetallic phase, morphology, size, area fraction and distribution were similar to that observed in the strontium modified alloy quenched before the start of the Al-Si eutectic reaction.

Place, publisher, year, edition, pages
Springer, 2019
Keywords
Aluminum alloys, Cooling, Eutectics, Intermetallics, Iron, Magnesium alloys, Platelets, Solidification, Strontium alloys, Al-7Si-0.3Mg alloys, Al-Si eutectic, Chinese script, Eutectic cells, Eutectic reactions, Intermetallic phase, Intermetallic phasis, Thin platelets, Silicon alloys
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-45391 (URN)10.1007/s11661-019-05343-5 (DOI)000477997600021 ()2-s2.0-85068741757 (Scopus ID)HOA JTH 2019 (Local ID)HOA JTH 2019 (Archive number)HOA JTH 2019 (OAI)
Funder
Vinnova, 2014-05096
Available from: 2019-07-23 Created: 2019-07-23 Last updated: 2019-08-15Bibliographically approved
Santos, J., Jarfors, A. E. .. & Dahle, A. (2019). Variation of properties in the cross-section of semi-solid al-7si-0.3mg castings. In: Rassili A.,Midson S.P.,Zhu Q.,Gang Hu X. (Ed.), Semi-Solid of Alloys and Composites: . Paper presented at 15th International conference on Semi-Solid Processing of Alloys and Composites, S2P 2018; Shenzhen; China; 22 - 24 October 2018 (pp. 81-86). Trans Tech Publications
Open this publication in new window or tab >>Variation of properties in the cross-section of semi-solid al-7si-0.3mg castings
2019 (English)In: Semi-Solid of Alloys and Composites / [ed] Rassili A.,Midson S.P.,Zhu Q.,Gang Hu X., Trans Tech Publications, 2019, p. 81-86Conference paper, Published paper (Refereed)
Abstract [en]

In semi-solid casting, a slurry consisting of primary α-Al crystals and liquid is injected into the die cavity. The solidification in the die-cavity occurs by the growth of the primary α-Al crystals formed during slurry preparation and in the shot sleeve, nucleation and growth of in-cavity solidified crystals and ends with the eutectic reaction. During solidification in the die cavity, the cooling rate near the die wall is higher in comparison to the centre of the casting, particularly for thick-walled castings. The solidification conditions for the slurry α-Al crystals that are closer to the die wall can be very different compared to the slurry α-Al crystals located at the casting centre. This can result in different solute concentration in the interior of the α-Al globules in different regions of the semi-solid casting cross-section and consequently, different response to heat treatament. The RheoMetal™ process was used to produce thick-walled semi-solid castings. Semi-solid castings in the as-cast and T6 conditions were investigated. Indentation tests for hardness measurements in the nano-range were performed in the interior of α-Al globules near the surface and at the casting cross-section centre. The hardness variation across the casting cross-section was evaluated by low-force Vickers hardness. The castings in the as-cast condition showed more uniform properties in the cross-section compared to the T6 condition. Additionally, the results suggest that microsegregation in the interior of α-Al globules is very low in castings in the as-cast and T6 conditions. 

Place, publisher, year, edition, pages
Trans Tech Publications, 2019
Series
Science, University and Society, ISSN 1653-6010
Series
Solid State Phenomena, ISSN 1012-0394, E-ISSN 1662-9779 ; 285
Keywords
Hardness, Heat treatment, Properties, Rheometal™, Semi-solid casting, Die casting machines, Dies, Vickers hardness, Eutectic reactions, Hardness measurement, Hardness variation, Nucleation and growth, Semi solid casting, Solidification condition, Solute concentrations, Solidification
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-42786 (URN)10.4028/www.scientific.net/SSP.285.81 (DOI)2-s2.0-85059953796 (Scopus ID)9783035713732 (ISBN)9783035733730 (ISBN)
Conference
15th International conference on Semi-Solid Processing of Alloys and Composites, S2P 2018; Shenzhen; China; 22 - 24 October 2018
Available from: 2019-01-31 Created: 2019-01-31 Last updated: 2019-01-31Bibliographically approved
Santos, J. (2018). Al-7Si-Mg semi-solid castings – microstructure and mechanical properties. (Licentiate dissertation). Jönköping: Jönköping University, School of Engineering
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
Santos, J., Kallien, L. H., Jarfors, A. E. .. & Dahle, A. (2018). Influence of grain refinement on slurry formation and surface segregation in semi-solid Al-7Si-0.3Mg castings. Metallurgical and Materials Transactions. A, 49A(10), 4871-4883
Open this publication in new window or tab >>Influence of grain refinement on slurry formation and surface segregation in semi-solid Al-7Si-0.3Mg castings
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
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-38689 (URN)10.1007/s11661-018-4787-9 (DOI)000443469700048 ()2-s2.0-85049646113 (Scopus ID)JTHMaterialIS (Local ID)JTHMaterialIS (Archive number)JTHMaterialIS (OAI)
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
Silva, F. J. G., Santos, J. & Gouveia, R. (2017). Dissolution of grain boundary carbides by the effect of solution annealing heat treatment and aging treatment on heat-resistant cast steel HK30. Metals, 7(7), Article ID 251.
Open this publication in new window or tab >>Dissolution of grain boundary carbides by the effect of solution annealing heat treatment and aging treatment on heat-resistant cast steel HK30
2017 (English)In: Metals, ISSN 2075-4701, Vol. 7, no 7, article id 251Article in journal (Refereed) Published
Abstract [en]

Decreasing the weight of heavy-duty vehicles is an ongoing concern. However, the need to deal with high temperatures in components such as manifolds imposes, by itself, some restrictions regarding material selection, being further limited when other required properties (e.g., functional, manufacturing or cost requirements) are taken into account. Cast austenitic stainless steels may represent a good choice in this context but the existence of concentrated chromium carbides can generate undesirable results. A good combination of heat treatments can be applied to cast heat-resistant austenitic stainless steels, in an effort to achieve the dispersion of fine carbides, consequently improving their microstructure, mechanical properties and creep resistance. In this work, an austenitic stainless steel usually used in high temperature applications was characterized and subjected to solution annealing and aging heat treatments. The material analyzed was the austenitic cast stainless steel HK30 and the goals of the work were to evaluate the effects of solution annealing heat treatments on the dissolution of grain boundary chromium carbides and the effects of aging treatments on creep resistance. The results show that the elimination of grain boundary chromium carbides is possible by applying a solution annealing heat treatment. Additionally, the precipitation of fine dispersed carbides is obtained after the aging treatment with an increase of hardness and, consequently, an expected improvement of creep resistance. Thus, the novelty presented by this work consists of selecting the best heat treatment combination in order to promote dispersion of carbides, thus avoiding further crack nucleation phenomena when parts are cyclically subjected to load and unload; this work also found the most adequate mechanical properties and achieved corrosion resistance regarding the application in heavy-duty vehicle components subjected to mechanical and thermal fatigue. By discovering methods of improving the properties of cast materials, large savings can be made both in terms of production costs as well as in the overall weight of the components.

Place, publisher, year, edition, pages
GOA JTH 2017: MDPI, 2017
Keywords
Aging heat treatment, Cast stainless steel, Grain boundary carbides, Intergranular corrosion, Solution annealing
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-37110 (URN)10.3390/met7070251 (DOI)000407365900022 ()2-s2.0-85022345808 (Scopus ID)JTHMaterialIS (Local ID)JTHMaterialIS (Archive number)JTHMaterialIS (OAI)
Available from: 2017-09-01 Created: 2017-09-01 Last updated: 2019-06-07Bibliographically approved
Santos, J., Jarfors, A. E. .. & Dahle, A. (2016). Filling, Feeding and Defect Formation of Thick-Walled AlSi7Mg0.3 Semi-Solid Castings. Paper presented at 14th International Conference on Semi Solid Processing of Alloys and Composites, October 23rd‐27th, Salt Lake City, Utah, USA.. Solid State Phenomena, 256, 222-227
Open this publication in new window or tab >>Filling, Feeding and Defect Formation of Thick-Walled AlSi7Mg0.3 Semi-Solid Castings
2016 (English)In: Solid State Phenomena, ISSN 1012-0394, E-ISSN 1662-9779, Vol. 256, p. 222-227Article in journal (Refereed) Published
Abstract [en]

Aluminium semi-solid castings have gained increased attention due to their superior mechanical properties, lower porosity compared to conventional high pressure die cast material. These characteristics suggests that semi-solid casting should be suitable to produce thick-walled structural components, yet most successful applications of semisolid casting have been for thin-walled components. There is a lack of understanding on filling and feeding related defect formation for semi-solid castings with thick-walled cross-sections. In the current study an AlSi7Mg0.3 aluminium alloy was used to produce semi-solid castings with a wall thickness of 10mm using a Vertical High Pressure Die Casting machine. The RheoMetalTM process was used for slurry preparation. The primary solid α-Al fraction in the slurry was varied together with die temperature. The evaluation of the filling related events was made through interrupted shots, stopping the plunger at different positions. Microscopy of full castings and interrupted test samples were performed identifying the presence of surface segregation layer, shear bands, gas entrapment, shrinkage porosity as well as burst feeding.

Place, publisher, year, edition, pages
Trans Tech Publications, 2016
Keywords
Aluminium Semisolid Casting, Burst Feeding, Feeding Mechanisms, Filling Mechanisms, Shear Bands, Solid Fraction, Thick-Walled Castings
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-31908 (URN)10.4028/www.scientific.net/SSP.256.222 (DOI)2-s2.0-85010196800 (Scopus ID)
Conference
14th International Conference on Semi Solid Processing of Alloys and Composites, October 23rd‐27th, Salt Lake City, Utah, USA.
Available from: 2016-10-04 Created: 2016-10-04 Last updated: 2018-08-16Bibliographically approved
Zhu, B., Santos, J., Jarfors, A. E. .. & Zanella, C.Influence of Mg content on the fatigue behaviour of Al-Si-Mg alloys by rheocasting process.
Open this publication in new window or tab >>Influence of Mg content on the fatigue behaviour of Al-Si-Mg alloys by rheocasting process
(English)Manuscript (preprint) (Other academic)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-43618 (URN)
Available from: 2019-05-09 Created: 2019-05-09 Last updated: 2019-05-09
Santos, J., Jarfors, A. E. .. & Dahle, A.The effect of magnesium on the intermetallic phases and heat treatment response of cast Al‐7Si‐Mg.
Open this publication in new window or tab >>The effect of magnesium on the intermetallic phases and heat treatment response of cast Al‐7Si‐Mg
(English)Manuscript (preprint) (Other academic)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-38691 (URN)
Available from: 2018-01-30 Created: 2018-01-30 Last updated: 2018-08-16
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-0260-5153

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