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Evaluating the plastic deformation of Al-Si-Cu-Mg casting alloys using the Hollomon and Ludwigson equations
Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
2011 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336Article in journal (Other academic) Submitted
Abstract [en]

The plastic part of true stress – true strain curves of three Al-Si casting alloys was evaluated using the Hollomon and Ludwigson equations. Three coarsenesses of the microstructure, two ageing temperatures and a number of ageing times were used. The Hollomon equation was able to describe the true stress – true strain curves for microstructures containing shearable precipitates, while the Ludwigson equation was needed for microstructures containing a supersaturated solid solution. A two bump shape appeared on the double logarithmic plot for the Al-Si-Cu alloy and the overaged Al-Si-Cu-Mg alloy. These curves could not be well described by the Hollomon or the Ludwigson equations.

Place, publisher, year, edition, pages
Maney Publishing , 2011.
Keywords [en]
Cast aluminium alloys; Plastic deformation; Artificial ageing; Hollomon; Ludwigson
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:hj:diva-16309OAI: oai:DiVA.org:hj-16309DiVA, id: diva2:447095
Available from: 2011-10-10 Created: 2011-10-10 Last updated: 2017-12-08Bibliographically 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. p. 45
Series
Doktorsavhandlingar vid Chalmers tekniska högskola, ISSN 0346-718X ; 3210
Keywords
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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Sjölander, EmmaSeifeddine, Salem

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