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Development of tools for integrated optimisation and use of aluminium alloys
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Commercial alloys are continuously developed to improve their performance. Therefore it is useful to establish new optimisation software, which could be used in development of new materials or in materials selection. In the first part of the thesis, mechanical and technological properties, which are of importance in materials selection in mechanical design, are investigated. Two types of materials are analysed for the mechanical properties, aluminium alloys and stainless steels but only aluminium alloys for the technological properties.

Thermodynamic analysis has been used to evaluate the effect of the microstructure. Solid solution hardening has been successfully modelled for both aluminium alloys and stainless steels following the theories by Labusch and Nabarro. The precipitation hardening is most dominant for the hardenable aluminium alloys, but the non-hardenable alloys also increase their strength from precipitation hardening. The non-hardenable alloys are divided into different tempers, which differ in the amount of strain hardening. This has also been modelled successfully.

Combining these fundamental results with multiple regressions, models for mechanical and technological properties have been created. Separate models are developed for wrought aluminium alloys and stainless steels. For the aluminium alloys these include the solid solution hardening and the precipitation hardening. For the stainless steels, the thickness, nitrogen content and ferrite content are included together with the solid solution hardening.

The second part of the thesis concerns materials selection and materials optimisation. Traditionally materials optimisation includes a preliminary sifting due to the vast number of engineering materials. Then there is a discriminating search followed by an optimisation. In the optimisation part the concept merit indices could be used to rank the materials. A merit index only includes material properties, as for example the characteristic strength, the density or the Young’s modulus. A concept related to the merit indices are the merit exponents, which can be used when no explicit functions for the merit indices are available. The merit exponents can also be used when creating a control area diagram (CAD). These diagrams are used as a design tool, where both the geometry and materials are taken into account. For a situation with several geometrical variables the merit exponents can give information of how much the target function will be influenced by a given property change. This technique can be used for a variety of situations, when there is more than one property limiting the final sizes of a component. Principles for setting up a CAD are given together with how the merit indices and exponents relate to the final CAD.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , vii, 9-61 p.
Keyword [en]
Aluminium alloys, Modelling, Materials optimisation, Mechanical properties
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-37609ISBN: 978-91-7501-068-7 (print)OAI: oai:DiVA.org:kth-37609DiVA: diva2:434463
Public defence
2011-09-09, F3, Lindstedtsvägen 26, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
QC 20110817Available from: 2011-08-17 Created: 2011-08-15 Last updated: 2011-08-17Bibliographically approved
List of papers
1. Modelling solid solution hardening in stainless steels
Open this publication in new window or tab >>Modelling solid solution hardening in stainless steels
2006 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 415, no 1-2, 66-71 p.Article in journal (Refereed) Published
Abstract [en]

The solid solution hardening of stainless steels is studied by using the Labusch-Nabarro relation. Models are evaluated in order to predict the mechanical properties from chemical composition, solution hardening misfit parameters, grain size, ferrite content and product thickness. A data source of six grades of steels is used for the modelling. Both austenitic and duplex stainless steels are covered including more than 1100 batches, which are subjected to multiple regression analyses. The models are compared with earlier studies and can be used as tools in material optimisation.

Keyword
stainless steel, material optimisation, solution hardening, mechanical properties, multiple regression
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-5737 (URN)10.1016/j.msea.2005.09.031 (DOI)000234270400009 ()2-s2.0-29244466485 (Scopus ID)
Note
QC 20100920Available from: 2006-05-15 Created: 2006-05-15 Last updated: 2017-12-14Bibliographically approved
2. Modelling mechanical properties for non-hardenable aluminium alloys
Open this publication in new window or tab >>Modelling mechanical properties for non-hardenable aluminium alloys
2007 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 41, no 1, 86-95 p.Article in journal (Refereed) Published
Abstract [en]

A range of mechanical properties have been investigated for non-hardenable aluminium alloys. Commercially pure aluminium, Al-Mn, and Al-Mg alloys in five tempers have been covered. In the models solid solution, particle strengthening and work hardening have been taken into account. Ab-initio calculations of the size and modulus misfit parameters that are needed in the solid solution hardening model have been performed. In accordance with the Labusch-Nabarro model, the solid solution hardening has been shown to be proportional to εL4 / 3 c2 / 3, where εL is the Fleischer misfit parameter and c the solute concentration. A cold work parameter H has been introduced. The contribution from cold working is linear in H for the tensile strength and fatigue endurance, whereas the contributions to the yield strength and to the hardness are proportional to H0.5.

Keyword
aluminium alloys, material optimisation, mechanical properties, solid solution, work hardening, particle strengthening, multiple regression
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-7601 (URN)10.1016/j.commatsci.2007.03.013 (DOI)000251041400011 ()2-s2.0-35348819299 (Scopus ID)
Note
QC 20100923Available from: 2007-11-12 Created: 2007-11-12 Last updated: 2017-12-14Bibliographically approved
3. One parameter model for strength properties of hardenable aluminium alloys
Open this publication in new window or tab >>One parameter model for strength properties of hardenable aluminium alloys
2008 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 29, no 8, 1540-1548 p.Article in journal (Refereed) Published
Abstract [en]

Models for strength properties are proposed for commercially aluminium alloys. The alloy group investigated are the hardenable alloys from the 2000 (Al-Cu and Al-Cu-Mg), 6000 (Al-Mg-Si) and 7000 (Al-Zn-Mg) series. The same model for solid solution hardening that has successfully been applied to non-hardenable alloys has been used. For precipitation hardening, particle cutting and the Orowan mechanism have been considered. The same basic model is used for all strength properties. It is demonstrated that with one fitting parameter for each property, a representation with reasonable accuracy can be obtained that is applicable to a wide range of alloys. Such models are useful in materials optimisation and selection.

Keyword
Material optimisation, Mechanical properties, Modelling, Particle strengthening, Solid solution hardening, Wrought aluminium alloys
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-7602 (URN)10.1016/j.matdes.2008.02.001 (DOI)000256895300007 ()2-s2.0-43049085490 (Scopus ID)
Note
QC 20100924. Uppdaterad från Submitted till Published (20100924).Available from: 2007-11-12 Created: 2007-11-12 Last updated: 2017-12-14Bibliographically approved
4. Modelling technological properties of commercial wrought aluminium alloys
Open this publication in new window or tab >>Modelling technological properties of commercial wrought aluminium alloys
2009 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 30, no 9, 3752-3759 p.Article in journal (Refereed) Published
Abstract [en]

The purpose of this paper is to model three important technological properties for aluminium alloys, based on their performance indices. The models are based on the chemical compositions and microstructure characteristics which are calculated using thermodynamical calculations. The properties that were modelled are the general corrosion, the weldability (MIG and TIC) and the machinability. The results from these models are to be used in materials selection and optimisation. The models clearly show that the general corrosion resistance is reduced for all alloy additions, except for small amounts of titanium. The largest influence on the corrosion is from copper and zinc. The weldability is negatively influenced by the copper and zinc-content, and for small additions of zirconium and titanium it is increased. The machinability is positively influenced by the hardness of the alloy or by adding lead or bismuth. For the non-heat-treatable alloys there was no influence from the composition to the corrosion resistance or the weldability. Copper and zinc which are added to increase the strength to the alloy strongly reduce both the weldability and the corrosion resistance but due to the increase in hardness increase the workability.

Keyword
Wrought aluminium alloys, Technological properties, Performance indices, corrosion behavior, machinability
Identifiers
urn:nbn:se:kth:diva-18595 (URN)10.1016/j.matdes.2009.02.004 (DOI)000267892200053 ()2-s2.0-67349212163 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
5. Merit exponents and control area diagrams in materials selection
Open this publication in new window or tab >>Merit exponents and control area diagrams in materials selection
2011 (English)In: Materials & Design, ISSN 0261-3069, Vol. 32, no 10, 4850-4856 p.Article in journal (Refereed) Published
Abstract [en]

Merit indices play a fundamental role in materials selection, since they enable ranking of materials. However, the conventional formulation of merit indices is associated with severe limitations. They are dependent on the explicit solution of the variables in the equations for the constraints from the design criteria. Furthermore, it is not always easy to determine which the controlling merit index is. To enable the ranking of materials in more general design cases, merit exponents are introduced as generalisations of the merit indices. Procedures are presented for how to compute the merit exponents numerically without having to solve equations algebraically. Merit exponents (and indices) are only valid in a certain range of property values. To simplify the identification of the controlling merit exponent, it is suggested that so called control area diagrams are used. These diagrams consist of a number of domains, each showing the active constraints and the controlling merit exponent. It is shown that the merit exponents play a crucial role when the control area diagram (CAD) is set up. The principles in the paper are developed for mechanically loaded components and are illustrated for engineering beams with two or three geometric variables.

Keyword
Material selection charts, Performance indices
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-37638 (URN)10.1016/j.matdes.2011.06.013 (DOI)000294373500024 ()2-s2.0-79960902712 (Scopus ID)
Note

QC 20110815

Available from: 2011-08-15 Created: 2011-08-15 Last updated: 2012-08-23Bibliographically approved
6. Materials selection for a cooling plate using control area diagrams
Open this publication in new window or tab >>Materials selection for a cooling plate using control area diagrams
2011 (English)In: Materials & Design, ISSN 0261-3069, Vol. 32, no 10, 4866-4873 p.Article in journal (Refereed) Published
Abstract [en]

Merit indices are used to rank materials and are of fundamental importance in materials selection. Traditionally, merit indices have only been available for elementary design cases. In the present paper merit indices are generalised to cooling systems where heat flow and strength are design criteria in a materials optimisation framework. A cooling tube and a cooling plate are considered. A new concept, merit exponent is used that is related to the merit indices. A definition of the merit exponent is given also for cases with many design variables. In each design case a number of merit exponents are involved. It is a nontrivial task to identify which they are and when each of them is applicable. For this purpose control area diagrams (CAD) are used. A CAD is a diagram with the controlling properties on the axes, and areas where one or more constraints are active. For the cooling systems the controlling properties are heat conductivity and strength. The active constraints define the relevant merit exponent. The constraints involve the controlling properties and geometrical variables. Principles are established for how to set up the CAD and to derive the merit exponents.

Keyword
Aluminium alloys, Material selection charts, Performance indices
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-37639 (URN)10.1016/j.matdes.2011.06.008 (DOI)000294373500026 ()2-s2.0-79960923992 (Scopus ID)
Note

QC 20110815

Available from: 2011-08-15 Created: 2011-08-15 Last updated: 2012-08-23Bibliographically approved

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