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Rheocasting of Aluminium Alloys: Slurry Formation, Microstructure, and Properties
Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.ORCID iD: 0000-0001-6755-2123
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Innovative materials with novel properties are in great demand for use in the criticalcomponents of emerging technologies, which promise to be more cost-effective and energyefficient.A controversial issue with regard to manufacturing complex industrial products isto develop advanced materials with optimised manufacturability in addition to the requiredmechanical and physical properties. The objective of this research study was to develop andoffer new solutions in material-processing-related issues in the field of mechanical andelectrical engineering. This was achieved by investigating the new opportunities affordedby a recently developed rheocasting method, RheoMetalTM process, with the goal of comingto an understanding of the critical factors for effective manufacturing process.

A study of the evolution of microstructure at different stages of the rheocasting process,demonstrated the influence of multistage solidification on the microstructural characteristicsof the rheocast components. The microstructural investigation onquench slurry showed itconsists of the solute-lean coarse globular α-Al particles with uniform distribution ofalloying elements, suspended in the solute-rich liquid matrix. Such inhomogeneous slurryin the sleeve seems to play a critical role in the inhomogeneity of final microstructure. Inthe rheocast component, the separation of the liquid and solid parts of slurry during fillinginfluenced on the microstructural inhomogeneity.

The relationship between the microstructural characteristics and properties of the rheocastcomponents was investigated. The study on the fracture surfaces of the tensile-testedspecimens showed that the mechanical properties strongly affected by microstructuralinhomogeneity, in particular macrosegregation in the form of near surface liquid segregationbands and subsurface porosity. The thermal conductivity measurement showed variation ofthis property throughout the rheocast component due to variations in the ratio of solute-leanglobular α-Al particles and fine solute α-Al particles. The result showed silicon in solidsolution have a strong influence (negative) on thermal conductivity and precipitation ofsilicon by heat treatment process increase the thermal conductivity.

Place, publisher, year, edition, pages
Jönköping: Jönköping University, School of Engineering , 2015. , 50 p.
Series
JTH Dissertation Series, 6
Keyword [en]
SSM Casting, aluminium alloy, RheoMetalTM process, microstructure, physical and mechanical properties
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:hj:diva-26297ISBN: 978-91-87289-07-1 (print)OAI: oai:DiVA.org:hj-26297DiVA: diva2:800320
Presentation
2015-04-24, E1405, Tekniska Högskolan, Högskolan i Jönköping, Jönköping, 14:36 (English)
Opponent
Supervisors
Projects
RheoCom
Funder
Knowledge Foundation, 20100203
Available from: 2015-04-08 Created: 2015-03-30 Last updated: 2016-08-12Bibliographically approved
List of papers
1. Effect of superheat on melting rate of EEM of Al alloys during stirring using the RheoMetal process
Open this publication in new window or tab >>Effect of superheat on melting rate of EEM of Al alloys during stirring using the RheoMetal process
2013 (English)In: Solid State Phenomena, ISSN 1012-0394, E-ISSN 1662-9779, Vol. 192-193, 392-397 p.Article in journal (Refereed) Published
Abstract [en]

The RheoMetal process (previously called the Rapid S- and RSF- process) is a novelmethod to produce cost effective, high quality, semisolid slurries for component casting. TheRheoMetal process uses an Enthalpy Exchange Material (EEM) as cooling agent to absorb heat andproduce a slurry. Critical process parameters to create a slurry by robust melting of the EEM arealloy content, stirring speed, EEM to melt ratio, EEM temperature, EEM microstructuralcharacteristics and melt superheat.In this paper, the melting sequence and melting rate of the EEM was studied experimentally. Theeffect of EEM composition, as well as superheat, on evolution of shape and dimension of the EEMduring stirring was investigated. Initial material freezing onto the EEM was observed, followed by astationary phase with subsequent gradual melting of the EEM. It was shown that the characteristicsof freeze-on layer were strongly correlated to melt superheat, EEM temperature, as well as materialcomposition, hence also has significant influence on the melting sequence.

Keyword
Semi-Solid casting, melting, non-dendritic slurry, RheoMetal Process, Experimental Design, Rapid S, RSF
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-19514 (URN)10.4028/www.scientific.net/SSP.192-193.392 (DOI)000315930600060 ()2-s2.0-84870797417 (Scopus ID)
Projects
RheoCom
Available from: 2012-09-27 Created: 2012-09-25 Last updated: 2016-08-22Bibliographically approved
2. Influence of Microstructural Inhomogeneity on Fracture Behaviour in SSM-HPDC Al-Si-Cu-Fe Component with Low Si Content
Open this publication in new window or tab >>Influence of Microstructural Inhomogeneity on Fracture Behaviour in SSM-HPDC Al-Si-Cu-Fe Component with Low Si Content
2015 (English)In: Solid State Phenomena, ISSN 1012-0394, E-ISSN 1662-9779, Vol. 217-218, 67-74 p.Article in journal (Refereed) Published
Abstract [en]

In the current paper, a low-Si aluminium alloy (1.4-2.4% Si) was used to fabricate acomplex shape telecom component using Semi-Solid High-Pressure Die Cast (SSM-HPDC),process. Microstructure and fracture characteristics were investigated. The cast material exhibitedmicrostructural inhomogeneity, in particular macrosegregation in the form of liquid surfacesegregation bands in addition to sub-surface pore bands and gross centre porosity. Tensilespecimens were taken from the cast components. Elongation and microstructural inhomogeneitywere investigated and correlated. Fracture surfaces of the tensile specimen were examined underscanning electron microscope (SEM). The study showed that both near surface liquid segregationbands and subsurface porosity strongly affected the fracture behaviour. Dominant for loss ofductility was gross centre porosity. The centre porosity was found to be a combination of trappedgas and insufficient, irregular feeding patterns.

Place, publisher, year, edition, pages
Switzerland: Trans Tech Publications Inc., 2015
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-24393 (URN)10.4028/www.scientific.net/SSP.217-218.67 (DOI)2-s2.0-84914151681 (Scopus ID)
Projects
RheoCom
Funder
Knowledge Foundation
Available from: 2014-08-21 Created: 2014-08-21 Last updated: 2016-08-22Bibliographically approved
3. Mechanical And Thermal Properties Of Rheocast Telecom Component Using Low Silicon Aluminium Alloy In As-Cast And Heat-Treated Conditions
Open this publication in new window or tab >>Mechanical And Thermal Properties Of Rheocast Telecom Component Using Low Silicon Aluminium Alloy In As-Cast And Heat-Treated Conditions
2015 (English)In: Light Metals 2015 / [ed] Margaret Hyland, Hoboken, NJ: John Wiley & Sons, 2015Conference paper, (Refereed)
Abstract [en]

The growing demand for increasingly more cost and energy effective electronics components is a challenge for the manufacturing industry. To achieve higher thermal conductivity in telecom components, an aluminum alloy with a composition of Al-2Si-0.8Cu-0.8Fe-0.3Mn was created for rheocasting. Yield strength and thermal conductivity of the material were investigated in the as cast, T5 and T6 heat-treated conditions. The results showed that in the as-cast condition thermal conductivity of 168 W/mK and yield strength of 67 MPa was achieved at room temperature. A T5 treatment at 200°C and 250°C increased thermal conductivity to 174 W/mK and 182 W/mK, respectively, while only a slight increase in yield strength was observed. Moreover, a T6 treatment resulted in similar thermal conductivity as the T5 treatment at 250°C with no significant improvement in yield strength. Therefore, the T5 treatment at 250°C was suggested as an optimum condition for the current alloy composition.

Place, publisher, year, edition, pages
Hoboken, NJ: John Wiley & Sons, 2015
Keyword
SSM HPDC, Thin-wall component, RheoMetal process, Thermal conductivity, Heat treating process
National Category
Engineering and Technology
Identifiers
urn:nbn:se:hj:diva-24859 (URN)10.1002/9781119093435.ch37 (DOI)9781119082446 (ISBN)9781119093435 (ISBN)
Conference
TMS 2015 144th Annual Meeting & Exhibition
Funder
Knowledge Foundation
Available from: 2014-10-08 Created: 2014-10-08 Last updated: 2016-08-22Bibliographically approved
4. Solidification sequence and evolution of microstructure during rheocasting of four Al-Si-Mg-Fe alloys with Low Si content
Open this publication in new window or tab >>Solidification sequence and evolution of microstructure during rheocasting of four Al-Si-Mg-Fe alloys with Low Si content
2016 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 47, no 3, 1215-1228 p.Article in journal (Refereed) Published
Abstract [en]

Four Al-Si-Mg-Fe alloys with Si contents varying from 1.6 to 4.5 wt pct were rheocast, using the RheoMetal™ process to prepare slurry and cast in a vertical high-pressure die casting machine. Particle size and Si concentration in the α-Al particles in the slurry and in the as-rheocast component were investigated. A uniform distribution of Si in the globular α 1-Al particles was achieved in the slurry. In the rheocast samples, measurement of the α 1-Al particles showed that these particles did not increase significantly in size during pouring and secondary solidification. The two additional α-Al particles types, α 2-Al particles and α 3-Al particles, were identified as being a result of two discrete nucleation events taking place after slurry production. The Si concentration in the α 2-Al and α 3-Al particles indicated that the larger α 2-Al particles precipitated before the α 3-Al particles. In addition, in the as-rheocast condition, the Si distribution inside the α 1-Al particles showed three distinct zones; an unaffected zone, a transition zone, and in some cases the start of a dendritic/cellular zone. The phenomenon of dendritic growth of globular α 1-Al particles during secondary solidification occurred concomitantly with the final eutectic reaction and increased with increasing amount of the Al-Si eutectic phase.

National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-26312 (URN)10.1007/s11661-015-3290-9 (DOI)2-s2.0-84951985830 (Scopus ID)
Note

Submitted (and included in licentiate thesis) under the name: Solidification sequence and evolution of microstructure during rheocasting of Al-Si-Mg-Fe alloys with low Si content

Available from: 2015-04-08 Created: 2015-04-08 Last updated: 2016-08-22Bibliographically approved
5. Thermal conductivity of liquid cast and rheocast telecom component using Al-6Si-2Cu-Zn (Stenal Rheo 1) in as-cast and heat treated condition
Open this publication in new window or tab >>Thermal conductivity of liquid cast and rheocast telecom component using Al-6Si-2Cu-Zn (Stenal Rheo 1) in as-cast and heat treated condition
2015 (English)Report (Other academic)
Abstract [en]

The thermal conductivity of a rheocast telecom component produced using Al-6Si-2Cu-Zn alloy (Stenal Rheo 1) was investigated in the as-cast, T5 and T6 conditions. Conventionally liquid cast samples were produced in a permanent mold and used as a reference material. In the rheocast component in as-cast condition, a thermal conductivity of 153 W/mK at room temperature were measured. A T5 treatment at 250 or 300°C increased thermal conductivity to 174 W/mK. A T6 treatment resulted in further increase in thermal conductivity to 182 W/mK. The liquid cast alloy exhibited a lower thermal conductivity and a higher hardness for all conditions compared to the as-rheocast component.The microstructure of rheocast component showed material consisted of relatively large α1-Al particles formed during the slurry fabrication process and fine α2-Al particles formed in the die cavity. The macrosegregation in the form of the different ration of the primary α1-Al particles to secondary α2-Al particles in different positions of the rheocast component was observed. The relation between microstructural characteristics and thermal diffusivity was investigated by determining the local thermal conductivity in the rheocast component and ration of α1-Al particles to α2-Al particles. The results revealed that samples from the regions of the component with a high amount of α1-Al particles had a higher thermal conductivity. WDS measurement results pointed to that Si and Cu concentration in the α1-Al particles contained lower concentrations value compare to the α2-Al particles and therefore α1-Al particles has higher value for thermal conductivity.Silicon precipitation was confirmed using calorimetry and dilatometry to take place between 200 and 250°C. A linear relation between the fraction of Si precipitates formed and the increase in thermal diffusivity was obtained. Silicon in solid solution is shown to have a strong influence (negative) on thermal conductivity. When the silicon is precipitated by heat treatment the thermal conductivity increases. For an optimal combination of thermal and mechanical properties it is therefore important to use an ageing temperature above the temperature for Si precipitation.

Place, publisher, year, edition, pages
Jönköping: Jönköping University, School of Engineering, 2015. [19] p.
Series
JTH research report, ISSN 1404-0018 ; 2015-01
Keyword
Thermal conductivity, Microstructure characteristics, Stenal Rheo1 alloy, Rheo-casting, High pressure die-casting
National Category
Engineering and Technology
Identifiers
urn:nbn:se:hj:diva-26296 (URN)
Funder
Knowledge Foundation, 20100203
Available from: 2015-03-30 Created: 2015-03-30 Last updated: 2016-08-12Bibliographically approved

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