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On the complexity of the relationship between microstructure and tensile properties in cast aluminum
Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.ORCID iD: 0000-0001-6481-5530
Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.ORCID iD: 0000-0002-0101-0062
2015 (English)In: International Journal of Modern Physics B, ISSN 0217-9792, Vol. 29, no 10-11, article id 1540011Article in journal (Refereed) Published
Abstract [en]

The relationship between microstructure and mechanical properties in cast aluminium alloys is very complex. This relationship is also strongly affected by the casting process and melt handling. In the current study the mechanical properties were investigated and correlated with microstructural features such as porosity, Fe-rich particles, SDAS, Si-length. Process quality measures such as bifilm index, density index, and sludge factor were also investigated. The aim of the work was to understand the critical interactions between material microstructure and process quality in the development of high performance materials.

Place, publisher, year, edition, pages
2015. Vol. 29, no 10-11, article id 1540011
Keywords [en]
imperfections, defects, porosity, fe-rich, sdas, silicon, bifilm, density, sludge, mechanical, properties, aluminium, aluminum
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:hj:diva-24687DOI: 10.1142/S0217979215400111ISI: 000353523600012Scopus ID: 2-s2.0-84928555789OAI: oai:DiVA.org:hj-24687DiVA, id: diva2:774493
Conference
Asia Pacific Conference on Materials Processing 2014
Available from: 2014-12-23 Created: 2014-09-09 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Imperfections in Recycled Aluminium-Silicon Cast Alloys
Open this publication in new window or tab >>Imperfections in Recycled Aluminium-Silicon Cast Alloys
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In striving to produce high quality cast components from recycled aluminium alloys,imperfections have to be considered, because recycled aluminium usually containsmore of it. However, there are great energy savings to be made by using recycledaluminium; as little as 5% of the energy needed for primary aluminium productionmay be required. High quality castings are dependent on, besides alloy chemistry, bothmelt quality and the casting process; the focus of this work is related to the meltquality.This thesis aims to increase knowledge about imperfections, foremost about Fe-richparticles, oxides/bifilms, and porosity. Experiments were performed at industrialfoundry facilities and in a laboratory environment. Melt quality was evaluated byproducing samples with the reduced pressure test (RPT), from which both densityindex (DI) and bifilm index (BI) could be measured, results that were related to tensiletest properties. Data from tensile test samples were analysed, and fracture surfacesand cross sections were studied in both light microscope and in scanning electronmicroscope (SEM). For the purpose of investigating nucleation of primary Fe-richparticles (sludge) differential scanning calorimetry (DSC) was used.In the analysis of results, a correlation between the morphology of particles and tensileproperties were found. And elongated Fe-rich β-particles were seen to fracturethrough cleavage towards the centre. However, DI and BI have not been possible torelate to tensile properties.The nucleation temperature of primary Fe-rich particles were found to increase withincreased Fe, Mn, and Cr contents, i.e. the sludge factor (SF), regardless of cooling rate.For a set SF, an increase of cooling rate will decrease the nucleation temperature.

Place, publisher, year, edition, pages
Jönköping: Jönköping University, School of Engineering, 2015. p. 39
Series
JTH Dissertation Series ; 8
Keywords
Imperfections, Recycled cast Al-Si alloy, Fe-rich particles, Melt quality, Fractography, Differential scanning calorimetry.
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-26790 (URN)978-91-87289-09-5 (ISBN)
Presentation
2015-06-12, E1405, Jönköping University, School of Engineering, Jönköping, 10:00 (English)
Opponent
Supervisors
Available from: 2015-06-01 Created: 2015-05-28 Last updated: 2017-01-09Bibliographically approved
2. On the influence of imperfections on microstructure and properties of recycled Al-Si casting alloys
Open this publication in new window or tab >>On the influence of imperfections on microstructure and properties of recycled Al-Si casting alloys
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

There are great energy savings to be made by recycling aluminium; as little as 5% of the energy needed for primary aluminium production may be required. Striving to produce high quality aluminium castings requires knowledge of microstructural imperfections, which is extra important when casting recycled aluminium that generally contains higher levels of imperfections compared to primary aluminium. Imperfections include amongst others Si, Fe, and Mn as well as oxides. Si is needed for castability, but it may also initiate fracture. There are different types of Fe-rich intermetallics influencing properties of castings, generally in a negative direction. Oxides constitute cracks and they are elusive because they are difficult to quantify.

This thesis aims to increase knowledge about imperfections in recycled aluminium castings originating from alloying elements and the melt. Experiments were performed in advanced laboratory equipment, including X-radiographic imaging during solidification and in-situ tensile testing in a scanning electron microscope. Experiments were also performed at industrial foundry facilities.

The experiments showed that the nucleation temperature of primary α-Fe intermetallics increased with higher Fe, Mn, and Cr contents. Primary α-Fe are strongly suggested to nucleate on oxides and to grow in four basic morphologies. Lower nucleation frequency of α-Fe promoted faster growth and hopper crystals while higher nucleation frequency promoted slower growth rates and massive crystals. Results also showed that a decrease in the size of the eutectic Si and plate-like β-Fe intermetallics improved tensile properties, foremost the elongation to fracture. In β-Fe containing alloys the transversely oriented intermetallics initiated macrocracks that are potential fracture initiation sites. In alloys with primary α-Fe foremost clusters of intermetallics promoted macrocracks. In fatigue testing, a transition from β-Fe to α-Fe shifted the initiation sites from oxides and pores to the α-Fe, resulting in a decrease of fatigue strength. Oxides in Al-Si alloys continue to be elusive; no correlations between efforts to quantify the oxides and tensile properties could be observed.

Abstract [sv]

Genom att återvinna aluminium kan stora energibesparingar göras eftersom återvinning kan förbruka så lite som 5% av den energi som behövs för produktion av primär aluminium. Vid gjutning av högkvalitativa aluminiumprodukter krävs förståelse för defekter i mikrostrukturen och denna kunskap är extra viktig vid användning av återvunnen aluminium, som i regel innehåller mer defekter än primär aluminium. Defekterna består bland annat av Si, Fe och Mn samt oxider. Si behövs för gjutbarhet men kan också initiera brott. Järnrika intermetaller kan ha olika morfologier som generellt påverkar gjutna komponenter negativt. Oxider, som kan utgöra sprickor, är gäckande då de är svåra att kvantifiera.

Denna avhandlings syfte är att öka kunskapen om defekter i gjutna komponenter av återvunnen aluminium. Experiment utfördes med avancerad laborationsutrustning så som röntgenfotografering av prover under stelning och dragprovning i svepelektronmikroskop. Experiment utfördes också i industrimiljö.

Experimenten visade att kärnbildningstemperaturen steg för primära α-Fe intermetaller med ökade andelar av Fe, Mn och Cr. Resultaten tyder starkt på att primär α-Fe kärnbildas på oxider och att de växer i fyra olika morfologier. Lägre kärnbildningstäthet av α-Fe främjade snabbare tillväxt av kristaller med håligheter men högre kärnbildningstäthet främjade långsammare tillväxt av massiva kristaller. Resultaten visade också att minskad storlek av eutektiskt Si och β-Fe intermetaller ledde till förbättring av dragprovsresultaten, främst brottförlängningen. I legeringar med β-Fe ledde transversellt orienterade intermetaller till makrosprickor vilka kan initiera brott. I legeringar med primär α-Fe var det främst kluster av intermetaller som orsakade makrosprickor. I utmattningsprovning orsakade modifiering av β-Fe till α-Fe förflyttning av sprickinitieringen från oxider och porer till α-Fe, vilket resulterade i en reducerad utmattningshållfasthet. Oxiderna i Al-Si-legeringar fortsätter att gäcka; ingen korrelation mellan försök att kvantifiera oxiderna och draghållfasthet kunde påvisas.

Place, publisher, year, edition, pages
Jönköping: Jönköping University, School of Engineering, 2017. p. 67
Series
JTH Dissertation Series ; 28
Keywords
Imperfections, Recycled Al-Si alloys, Fe-rich intermetallics, Melt quality, Fractography, Defekter, Återvunna Al-Si legeringar, Fe-rika intermetaller, Smältakvalité, Fraktografi
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-36963 (URN)978-91-87289-29-3 (ISBN)
Public defence
2017-09-15, E1405 (Gjuterisalen), Tekniska Högskolan, Jönköping, 10:00
Opponent
Supervisors
Available from: 2017-08-21 Created: 2017-08-21 Last updated: 2017-08-21Bibliographically approved

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Bjurenstedt, AntonSeifeddine, SalemJarfors, Anders

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