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The effect of microstructural inhomogeneity on thermal diffusivity in a rheocast component
Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting. (RheoCom)ORCID iD: 0000-0001-6755-2123
Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting. (RheoCom)ORCID iD: 0000-0002-0101-0062
Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting. RheoMetal. (CompCast)
2016 (English)In: La Metallurgia Italiana, ISSN 0026-0843, Vol. 108, no 6, 57-60 p.Article in journal (Refereed) Published
Abstract [en]

The relationship between microstructural characteristics and thermal diffusivity of a rheocast component was investigated for two Al-Si-Mg-Fe alloys with low Si contents. The microstructural investigation of the components clearly depicted the formation of coarse solute-lean globular α1-Al particles during the slurry fabrication process and fine solute-rich α2-Al and α3-Al particles during the secondary solidification in the die cavity. The microstructural characterization was quantified based on the amount of α1-Al particles in different locations of the component. The result clearly revealed a presence of both longitudinal and transverse macrosegregation of solute-lean α1-Al particles in the rheocast component. The study of thermal diffusivity and hardness revealed that the regions of the component with a high fraction of α1-Al particles had a higher thermal diffusivity but a lower hardness. Silicon in the solid solution was observed to be a critical factor in reducing the thermal diffusivity. The comparison between the effect of longitudinal and transverse segregation on thermal diffusivity showed that the transverse segregation had a stronger impact.

Place, publisher, year, edition, pages
Milano: Associazione Italiana di Metallurgia , 2016. Vol. 108, no 6, 57-60 p.
Keyword [en]
SSM casting, Aluminium Alloys, Inhomogeneity, Microstructure, Hardness, Thermal Diffusivity
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:hj:diva-30581OAI: oai:DiVA.org:hj-30581DiVA: diva2:937884
Conference
High Tech Die Casting 2016, Venice, 22-23 June, 2016.
Projects
CompCastRheoCom
Funder
Knowledge Foundation, 20100280
Available from: 2016-06-16 Created: 2016-06-16 Last updated: 2017-02-02Bibliographically approved
In thesis
1. Rheocasting of aluminium alloys: Process and components characteristics
Open this publication in new window or tab >>Rheocasting of aluminium alloys: Process and components characteristics
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Semi-Solid Metal (SSM) casting is a promising technology offering an opportunity to manufacture net-shape, complex geometry metal components in a single operation. However, the absence of foundry guidelines and limited design data for SSM casting makes it challenging to predict the performance of both process and components. The objective of this research was to develop and offer new solutions to material processing-related issues in the electronics industry. By investigating the opportunities afforded by the recently developed RheoMetalTM rheocasting process, a better understanding of the critical factors needed for an effective manufacturing process and optimised component characteristics was achieved.

A study of the evolution of microstructure at different stages of the RheoMetalTM process demonstrated the influence of multistage solidification on the microstructural characteristics of the rheocast components. The microstructure of a slurry consists of the solute-lean and coarse globular α-Al particles with a uniform distribution of alloying elements, suspended in the liquid matrix. Additional solute-rich α-Al particles were identified as being a consequence of discrete nucleation events taking place after the initial slurry production. In the final components, macrosegregation was observed in the form of variations in the ratio of solute-lean coarse globular α-Al particles and solute-rich fine α-Al particles in both longitudinal and transverse directions.

The relation between microstructural characteristics and material properties was established by determination of the local properties of a rheocast component. The fracture of a rheocast telecom component was strongly affected by microstructural inhomogeneity. In particular, macrosegregation in the form of liquid surface segregation bands and sub-surface pore bands strongly affected the fracture behaviour. Thermal conductivity measurements revealed that regions of the component with a high amount of solute-lean globular α-Al particles showed higher thermal conductivity. The effect of the local variation in thermal conductivity on the thermal performance of a large rheocast heatsink was evaluated by simulation. The results clearly show the importance of considering material inhomogeneity when creating a robust component design.

Place, publisher, year, edition, pages
Jönköping: Jönköping University, School of Engineering, 2016. 45 p.
Keyword
Rheocasting, aluminium alloy, RheoMetal(TM) process, microstructural characteristics, component properties and performance, robust design process
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-31428 (URN)978-91-87289-16-3 (ISBN)
Public defence
2016-09-23, E1405, School of Engineering, Jönköping, 10:00 (English)
Opponent
Supervisors
Funder
Knowledge Foundation
Available from: 2016-08-22 Created: 2016-08-22 Last updated: 2016-08-22Bibliographically approved

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