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High Temperature Tensile Deformation Behaviour and Failure Process of an Al-Si-Cu-Mg Cast Alloy: The Microstructural Scale Effect
Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.ORCID iD: 0000-0002-1190-836X
Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.ORCID iD: 0000-0001-6481-5530
Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.ORCID iD: 0000-0002-0101-0062
2015 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 86, 361-370 p.Article in journal (Refereed) Published
Abstract [en]

In this study the high temperature tensile deformation behavior of a commercial Al–Si–Cu–Mg cast alloy was investigated. The alloy was cast with two different cooling rates which resulted in average secondary dendrite arm spacing of 10 and 25 μm, which is typical of the microstructure scale obtained from high pressure die casting and gravity die casting. Tensile tests were performed at different strain rates (10− 4 s− 1 to 10− 1 s− 1) and over a wide temperature range from ambient temperature to 500 °C. The fine microstructure had superior tensile strength and ductility compared to the coarse microstructure at any given temperature. The coarse microstructure showed brittle fracture up to 300 °C; the fracture mode in the fine microstructure was fully ductile above 200 °C. The fraction of damaged particles was increased by raising the temperature and/or by microstructure coarsening. Cracks arising from damaged particles in the coarse microstructure were linked in a transgranular-dominated fashion even at 500 °C. However, in the fine microstructure alloy the inter-dendritic fracture path was more prevalent. When the temperature was raised to 300 °C, the concentration of alloying elements in the dendrites changed. The dissolution rates of Cu- and Mg-bearing phases were higher in the fine microstructure.

Place, publisher, year, edition, pages
2015. Vol. 86, 361-370 p.
Keyword [en]
EN AC-46000 cast alloy; Elevated temperatures; Deformation behavior; Microstructure
National Category
Materials Engineering Metallurgy and Metallic Materials Manufacturing, Surface and Joining Technology
Identifiers
URN: urn:nbn:se:hj:diva-27374DOI: 10.1016/j.matdes.2015.07.084ISI: 000362862700047Scopus ID: 2-s2.0-84942244775OAI: oai:DiVA.org:hj-27374DiVA: diva2:824554
Available from: 2015-06-22 Created: 2015-06-22 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Al-Si Cast Alloys - Microstructure and Mechanical Properties at Ambient and Elevated Temperatures
Open this publication in new window or tab >>Al-Si Cast Alloys - Microstructure and Mechanical Properties at Ambient and Elevated Temperatures
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Swedish industry is a global leader in development and manufacture of automotive and aviation components where the usage of aluminium products is remarkable. In addition to manufacturing aluminium components, casting enables low-cost and low-emission production of complex geometry components with a range of sizes. Aluminium with Si as the major alloying element forms a class of alloys representing the most significant fraction of all cast products, for a wide range of applications due to an excellent combination of castability and mechanical properties, as well as good corrosion resistance, wear resistance and recyclability. The microstructure in Al-Si alloys strongly governs their mechanical properties. Several industrial practices such as eutectic modification and alloying are well-known to improve mechanical properties. Al-Si cast alloys generally suffer a lack of ductility and poor high temperature properties due to presence of either brittle or thermally unstable phases. The aim of this work is to study the explicit role of each microstructural constituent on the behaviour of Al-Si cast alloys at room and high temperatures. The results will accordingly highlight the potential for improvement in properties of such alloys.

Casting defects have an immediate and negative effect on the properties of Al-Si alloys and reducing the overall level of defects substantially improves tensile properties. An increased cooling rate refines all microstructural features and reduces volumetric porosity which leads to substantial improvement in tensile properties (e.g. Rm and εF) at any test temperature. Modification of eutectic Si-particles (through Sr-addition) generally has a positive effect on alloy ductility. Depression in eutectic growth temperature as a result of eutectic modification was found to be strongly correlated to the level of modification irrespective of coarseness of the microstructure.

Addition of transition metals (Ni-Ti-Zr-Cr-V) to Al-Si improves tensile strength, particularly at temperatures above 200 ºC caused by formation of thermally stable intermetallic compounds. Below 200 ºC however, a substantial potential for improvement through solute-reinforcement was obtained.

A physically-based constitutive model with a wide validity range was successfully developed to describe the flow behaviour of Al-Si alloys at different temperatures, as a reliable input for finite element simulation. 

Place, publisher, year, edition, pages
Jönköping: Jönköping University, School of Engineering, 2017. 66 p.
Series
JTH Dissertation Series, 21
Keyword
Aluminium cast alloys, eutectic modification, microstructural scale effect, transition metals, room and elevated temperatures tensile properties, physically-based constitutive model.
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-35185 (URN)978-91-87289-22-4 (ISBN)
Public defence
2017-04-07, E1405, School of Engineering, Gjuterigatan 5, 10:00 (English)
Opponent
Supervisors
Funder
Knowledge Foundation
Available from: 2017-03-13 Created: 2017-03-10 Last updated: 2017-03-14Bibliographically approved

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Zamani, MohammadrezaSeifeddine, SalemJarfors, Anders

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