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The role of transition metal additions on the ambient and elevated temperature properties of Al-Si alloys
Jönköping University, School of Engineering, JTH, Materials and Manufacturing. Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.ORCID iD: 0000-0002-1190-836X
Department of Industrial Engineering (DIN), Alma Mater Studiorum – University of Bologna, Bologna, Italy.
Department of Industrial Engineering (DIN), Alma Mater Studiorum – University of Bologna, Bologna, Italy.
Jönköping University, School of Engineering, JTH, Materials and Manufacturing. Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.ORCID iD: 0000-0001-6481-5530
2017 (English)In: Materials Science and Engineering. A, ISSN 0921-5093, Vol. 693, 42-50 p.Article in journal (Other academic) Published
Abstract [en]

The principal aim of the present study was to investigate the effects of small additions of several transition metals (Zr, Ni, Ti, V, Cr, La, Y and Nb) on the microstructure, tensile properties and failure mechanisms of as-cast Al-10Si alloys at ambient and elevated temperatures (200 and 250 °C). Transition metal addition led to the formation of (AlSi)3(TiZr), (AlSi)3(CrVTi), Al13(FeCrVTi)4Si4, (AlSi)3(CrV), Al9FeNi AlNbTiZr, AlSiV, AlSiYLa and AlSiZrTiNb phases which are thermally stable until incipient melting of the eutectic compound occurs. Addition of Zr, Ni, Ti, V and Cr gave a substantial improvement in tensile strength at 250 °C, but at the expense of reduced ductility. The strength of transition metals-containing alloys is strongly governed by the size and morphology rather than the volume fraction of the intermetallic phases formed. Large and irregular particles such as (AlSi)3(TiZr), (AlSi)3(CrVTi), AlNbTiZr and AlSiV provided inhomogeneity in the α-Al matrix and act as the principal source of stress concentration, playing an active role in crack initiation. Crack propagation was primarily controlled by plastic deformation of high cooling rate-refined dendrites and modified eutectic silicon particles.

Place, publisher, year, edition, pages
Elsevier, 2017. Vol. 693, 42-50 p.
Keyword [en]
Alloy development; Aluminum castings alloys; High temperature tensile properties; Microstructure; Thermally stable precipitates
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:hj:diva-35198DOI: 10.1016/j.msea.2017.03.084ScopusID: 2-s2.0-85016027369Local ID: JTHMaterialISOAI: oai:DiVA.org:hj-35198DiVA: diva2:1081357
Available from: 2017-03-14 Created: 2017-03-14 Last updated: 2017-04-12Bibliographically 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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