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Optimization of solution treatment of cast Al-7Si-0.3Mg and Al-8Si-3Cu-0.5Mg alloys
Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.ORCID iD: 0000-0001-6481-5530
2014 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 45, no 4, 1916-1927 p.Article in journal (Refereed) Published
Abstract [en]

The influence of solidification rate on the solution-treatment response has been investigated for an Al-7Si-0.3Mg alloy and an Al-8Si-3Cu-0.5Mg alloy. The concentrations of Mg, Cu, and Si in the matrix after different solution-treatment times were measured using a wavelength dispersive spectrometer. All Mg dissolves into the matrix for the Al-Si-Mg alloy when solution treated at 803 K (530 C) because the π-Fe phase is unstable and transforms into short β-Fe plates which release Mg. The Q-Al5Mg8Cu2Si6 phase do not dissolve completely at 768 K (495 C) in the Al-Si-Cu-Mg alloy and the concentration in the matrix reached 0.22 to 0.25 wt pct Mg. The distance between π-Fe phases and Al2Cu phases was found to determine the solution-treatment time needed for dissolution and homogenization for the Al-Si-Mg alloy and Al-Si-Cu-Mg alloy, respectively. From the distance between the phases, a dimensionless diffusion time was calculated which can be used to estimate the solution-treatment times needed for different coarsenesses of the microstructure. A model was developed to describe the dissolution and homogenization processes.

Place, publisher, year, edition, pages
2014. Vol. 45, no 4, 1916-1927 p.
Keyword [en]
Dissolution, Homogenisation, Cast aluminium, WDS
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:hj:diva-16311DOI: 10.1007/s11661-013-2141-9ISI: 000333525200030Scopus ID: 2-s2.0-84898857263OAI: oai:DiVA.org:hj-16311DiVA: diva2:447101
Available from: 2011-10-10 Created: 2011-10-10 Last updated: 2016-11-29Bibliographically 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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