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Influence of microstructure and heat treatment on thermal conductivity of rheocast and liquid die cast Al-6Si-2Cu-Zn alloy
Jönköping University, School of Engineering, JTH, Materials and Manufacturing. Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.ORCID iD: 0000-0001-6755-2123
Scania CV AB, Materials Technology, Södertälje, Sweden.
Jönköping University, School of Engineering, JTH, Materials and Manufacturing. Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.ORCID iD: 0000-0002-0101-0062
Jönköping University, School of Engineering, JTH, Materials and Manufacturing. Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
2016 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336, Vol. 29, no 4, 202-213 p.Article in journal (Refereed) Published
Resource type
Text
Abstract [en]

Thermal conductivity of a rheocast component made from Stenal Rheo1 (Al-6Si-2Cu-Zn) alloy was investigated in as-cast, T5 and T6 conditions. The thermal conductivity measurement in different locations showed variation of this property throughout the rheocast component. The results of microstructural investigation revealed that the ratio of solute-lean α1-Al particles formed during slurry preparation to fine solute-rich α2-Al particles formed during secondary solidification had significant influence on thermal conductivity. The reduced amount of solutes in the α1-Al particles was determined as the root cause of higher thermal conductivity. A linear relation between the fraction of precipitates and the increase in thermal conductivity was obtained and silicon in solid solution is shown to have a dominant influence. As silicon was precipitated during the heat treatment, thermal conductivity increased. For an optimal combination of thermal and mechanical properties, it is therefore important to use an ageing temperature above the temperature of Si precipitation.

Place, publisher, year, edition, pages
2016. Vol. 29, no 4, 202-213 p.
Keyword [en]
Aluminium alloy, High-pressure die casting, Microstructure characteristics, Rheocasting, Thermal conductivity, Aluminum, Aluminum alloys, Copper alloys, Die casting, Heat treatment, Microstructure, Silicon, Thermal conductivity of solids, Zinc, Ageing temperature, High pressure die casting, Microstructural investigation, Optimal combination, Si precipitations, Thermal and mechanical properties, Thermal conductivity measurements
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:hj:diva-31227DOI: 10.1080/13640461.2015.1125990ISI: 000378146800003ScopusID: 2-s2.0-84978732257OAI: oai:DiVA.org:hj-31227DiVA: diva2:952018
Available from: 2016-08-11 Created: 2016-08-11 Last updated: 2016-08-22Bibliographically 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)
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Knowledge Foundation
Available from: 2016-08-22 Created: 2016-08-22 Last updated: 2016-08-22Bibliographically approved

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