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As-cast AZ91D Magnesium Alloy Properties- Effect of Microstructure and Temperature
Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting. (Materials and Manufacturing)ORCID iD: 0000-0002-9886-9710
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Magnesium and magnesium alloys are used in a wide variety of structural applications including automotive, aerospace, hand tools and electronic industries thanks to their light weight, high specific strength, adequate corrosion resistance and good castability. Al and Zn are the primary alloying elements in commercial Mg alloys and commonly used in automotive industries. AZ91 is one of the most popular Mg alloys containing 9% Al and 1% Zn. Hence, lots of research have been done during last decades on AZ91D. However, the existing data concerning mechanical properties and microstructural features showed large scatter and is even contradictory. This work focused on the correlation between the microstructure and the mechanical properties of as-cast AZ91 alloy. An exhaustive characterization of the grain size, secondary dendrite arm spacing (SDAS) distribution, and fraction of Mg17Al12 using optical and electron backscattered diffraction (EBSD) was performed. These microstructural parameters were correlated to offset yield point (Rp0.2), fracture strength and elongation to fracture. It was understood that the intermetallic phase, Mg17Al12, plays an important role in determining the mechanical and physical properties of the alloy at temperature range from room temperature up to 190oC. It was realized that by increasing the Mg17Al12 content above 11% a network of intermetallic may form. During deformation this rigid network should break before any plastic deformation happen. Hence, increase in Mg17Al12 content resulted in an increase in offset yield point. The presence of this network was supported by study of thermal expansion behaviour of the alloy containing different amount of Mg17Al12. A physically-based model was adapted and validated in order to predict the flow stress behaviour of as-cast AZ91D at room temperature up to 190ºC for various microstructures. The model was based on dislocation glide and climb in a single-phase (matrix) material containing reinforcing particles. The temperature dependant variables of the model were quite well correlated to the underlying physics of the material.

Place, publisher, year, edition, pages
Jönköping: Jönköping University, School of Engineering , 2015.
Series
JTH Dissertation Series, 10
Keyword [en]
Magnesium alloys, As-cast, AZ91D, Mechanical properties, Microstructural scale effect, Physical modelling
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:hj:diva-28467ISBN: 978-91-87289-11-8 (print)OAI: oai:DiVA.org:hj-28467DiVA: diva2:876229
Presentation
2015-11-06, Room E1405, School of Engineering, Jönköping University, Jönköping, 10:00 (English)
Opponent
Supervisors
Available from: 2015-12-07 Created: 2015-12-02 Last updated: 2016-01-14Bibliographically approved
List of papers
1. Effects of microstructure on deformation behaviour of AZ91D cast alloy
Open this publication in new window or tab >>Effects of microstructure on deformation behaviour of AZ91D cast alloy
2014 (English)In: TMS 2014 Annual Meeting Supplemental Proceedings TMS, The Minerals, Metals & Materials Society, San Diego, February 16-20, 2014, John Wiley & Sons, 2014, 565-572 p.Conference paper, Published paper (Refereed)
Abstract [en]

The deformation behavior of AZ91D cast magnesium alloy was investigated using uniaxial tensile tests from room temperature up to 190°C and strain rates from 0.0001 up to 0.1 1/s. In present work gradient solidification in a Bridgeman furnace was employed to study the effect of initial microstructure on the tensile mechanical response of the AZ91D alloy. The furnace drawing rate was varied from minimum 0.3 to maximum 6 mm/s, which yielded a variation of SDAS from 4.2 up to 25 as well as a variation of the fraction of the γ -phase (Mg17Al12),. The effects of microstructural parameters such as SDAS and γ -phase morphology on the yield strength (YS), ultimate tensile strength (UTS) and hardening were investigated

Place, publisher, year, edition, pages
John Wiley & Sons, 2014
Series
TMS Annual Meeting
Keyword
AZ91D, Microstructure, Mechanical properties, Temperature, Strain rate, Phase fraction
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-28468 (URN)000354941300068 ()2-s2.0-84899708224 (Scopus ID)978-1-118-88972-5 (ISBN)
Conference
TMS 2014
Available from: 2015-12-02 Created: 2015-12-02 Last updated: 2017-12-12Bibliographically approved
2. Microstructural Scale Effects on Thermal Expansion Behaviour of Cast AZ91D
Open this publication in new window or tab >>Microstructural Scale Effects on Thermal Expansion Behaviour of Cast AZ91D
2015 (English)In: Magnesium Technology 2015 - TMS 2015 144th Annual Meeting and Exhibition, Orlando, March 15-19, 2015, Hoboken: John Wiley & Sons, 2015, 361-365 p.Conference paper, Published paper (Refereed)
Abstract [en]

The effect of microstructure on thermal expansion of AZ91D cast alloy was studied. Samples with equiaxed grains and a controlled secondary dendrite arm spacing (SDAS) were fabricated using gradient solidification. SDAS was chosen to represent the range ofmicrostructural scale found in sand castings down to that of high pressure die casting. Optical microscopy and electron backscatter diffraction (EBSD) were used for microstructural characterization. The relation between thermal expansion and microstructuralscale of existing phases precipitated, in particular grain size, SDAS and fraction of Mg17Al12 was analyzed.

Place, publisher, year, edition, pages
Hoboken: John Wiley & Sons, 2015
Keyword
AZ91D, Magnesium, Mg17Al12, Microstructure, Thermal expansion
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-28486 (URN)10.1002/9781119093428.ch67 (DOI)2-s2.0-84942124208 (Scopus ID)978-111908243-9 (ISBN)
Conference
Magnesium Technology 2015 - TMS 2015
Available from: 2015-12-07 Created: 2015-12-07 Last updated: 2017-12-12Bibliographically approved
3. Effect of Mg17Al12 content on mechanical properties of AZ91D cast alloy
Open this publication in new window or tab >>Effect of Mg17Al12 content on mechanical properties of AZ91D cast alloy
(English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456Article in journal (Refereed) Submitted
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-28487 (URN)
Available from: 2015-12-07 Created: 2015-12-07 Last updated: 2017-12-12
4. Dislocation Density Model for Flow Stress of AZ91D Magnesium Alloy-Effect of Temperature and Microstructure
Open this publication in new window or tab >>Dislocation Density Model for Flow Stress of AZ91D Magnesium Alloy-Effect of Temperature and Microstructure
Show others...
(English)In: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154Article in journal (Refereed) Submitted
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-28489 (URN)
Available from: 2015-12-07 Created: 2015-12-07 Last updated: 2017-12-01

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Dini, Hoda

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