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Optimisation of solution treatment of cast Al–Si–Cu alloys
Jönköping University, School of Engineering, JTH. Research area Materials and Manufacturing - Casting. Jönköping University, School of Engineering, JTH, Mechanical Engineering.
Jönköping University, School of Engineering, JTH. Research area Materials and Manufacturing - Casting. Jönköping University, School of Engineering, JTH, Mechanical Engineering.ORCID iD: 0000-0001-6481-5530
2010 (English)In: Materials & design, ISSN 0264-1275, Vol. 31, no suppl. 1, 44-49 p.Article in journal (Refereed) Published
Abstract [en]

The influence of solidification rate on the solution treatment response for an Al–8Si–3.1Cu alloy has been investigated. The alloy was cast using the gradient solidification technique to produce samples with three different solidification rates. The samples were solution treated at 495 C for various times between 10 min and 10 h. The concentration of copper in the matrix was measured using the wavelength dispersive spectroscopy technique, WDS.

The results show that the coarseness of the microstructure clearly affects the solution treatment time needed to dissolve particles and obtain a homogenous distribution of copper in the matrix. A short solution treatment time of 10 min is enough to achieve a high and homogenous copper concentration for a material with a fine microstructure (secondary dendrite arm spacing, SDAS of 10 μm), while more than 10 h is needed for a coarse microstructure (SDAS of 50 μm). A model was developed to describe the dissolution and homogenisation process. The model shows good agreement with the experimental results.

Place, publisher, year, edition, pages
Elsevier , 2010. Vol. 31, no suppl. 1, 44-49 p.
Keyword [en]
Cast aluminium alloys, Solution treatment, Microstructure, Diffusion, WDS, Dissolution, Homogenisation
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:hj:diva-11307DOI: 10.1016/j.matdes.2009.10.035OAI: oai:DiVA.org:hj-11307DiVA: diva2:286567
Available from: 2010-01-14 Created: 2010-01-14 Last updated: 2015-10-02Bibliographically approved
In thesis
1. Heat treatment of Al-Si-Cu-Mg casting alloys
Open this publication in new window or tab >>Heat treatment of Al-Si-Cu-Mg casting alloys
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Environmental savings can be made by increasing the use of aluminium alloys in the automotive industry as the vehicles can be made lighter. Increasing the knowledge about the heat treatment process is one task in the direction towards this goal. The aim of this work is to investigate and model the heat treatment process for Al-Si casting alloys. Three alloys containing Mg and/or Cu were cast using the gradient solidification technique to achieve three different coarsenesses of the microstructure and a low amount of defects.

Solution treatment was studied by measuring the concentration of Mg, Cu and Si in the α-Al matrix using wavelength dispersive spectroscopy (WDS) after various times at a solution treatment temperature. A diffusion based model was developed which estimates the time needed to obtain a high and homogenous concentration of alloying elements for different alloys, temperatures and coarsenesses of the microstructure. It was shown that the yield strength after artificial ageing is weakly dependent on the coarseness of the microstructure when the solution treatment time is adjusted to achieve complete dissolution and homogenisation.

The shape and position of ageing curves (yield strength versus ageing time) was investigated empirically in this work and by studying the literature in order to differentiate the mechanisms involved. A diffusion based model for prediction of the yield strength after different ageing times was developed for Al-Si-Mg alloys. The model was validated using data available in the literature. For Al-Si-Cu-Mg alloys further studies regarding the mechanisms involved need to be performed.

Changes in the microstructure during a heat treatment process influence the plastic deformation behaviour. The Hollomon equation describes the plastic deformation of alloys containing shearable precipitates well, while the Ludwigson equation is needed when a supersaturated solid solution is present. When non-coherent precipitates are present, none of the equations describe the plastic deformation well. The evolution of the storage rate and recovery rate of dislocations was studied and coupled to the evolution of the microstructure using the Kocks-Mecking strain hardening theory.

Place, publisher, year, edition, pages
Göteborg: Chalmers Reproservice, 2011. 45 p.
Series
Doktorsavhandlingar vid Chalmers tekniska högskola, ISSN 0346-718X ; 3210
Keyword
Cast aluminium alloys, Heat treatment, Solution treatment, Artificial ageing, Tensile properties, Plastic deformation, Microstructure, Modelling
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-15695 (URN)978-91-7385-529-7 (ISBN)
Public defence
2011-05-20, 10:00 (Swedish)
Opponent
Supervisors
Available from: 2011-10-11 Created: 2011-07-13 Last updated: 2011-12-14Bibliographically approved

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