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Effects of microstructure and defects on tensile and fracture behaviour of a HPDC component: Potential properties and actual outcome of En AC-44300 alloy
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
2014 (English)In: Light Metals 2014 / [ed] J. F. Grandfield, John Wiley & Sons, 2014Conference paper, Published paper (Refereed)
Abstract [en]

The aim of present work is to study the influence of microstructure and defects on the mechanical properties of a structural high pressure die cast (HPDC) component of a commercial Al-Si based foundry alloy, EN AC-44300. The alloy which contains mainly 12% Si and 0.7% Fe, is a successful application of a die-casting alloy for the automotive market. Tensile test specimens were extracted from both high pressure die cast components and from ones with comparable microstructures produced through gradient solidification technique, which offers specimens with low levels of defects. The microstructure and defects available in the component were well mapped via X-ray inspection system, optical and scanning electron microscopy.  The results clearly confirmed the components’ performance dependency to configuration of defects and Si morphology as well as revealed the potential of the alloy in terms of ultimate tensile strength and ductility.

Place, publisher, year, edition, pages
John Wiley & Sons, 2014.
Keywords [en]
Microstructure, Casting defects, Porosity, HPDC component, Aluminum alloy
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:hj:diva-22814Scopus ID: 2-s2.0-84899859397ISBN: 978-1-118-88908-4 (print)OAI: oai:DiVA.org:hj-22814DiVA, id: diva2:680554
Conference
TMS 2014, 143rd Annual Meeting & Exhibition, February 16-20, 2014: San Diego, CA, USA
Projects
CompCAST
Funder
Knowledge FoundationAvailable from: 2013-12-18 Created: 2013-12-18 Last updated: 2017-03-14Bibliographically approved
In thesis
1. Al-Si Cast Alloys - Microstructure and Mechanical Properties at Ambient and Elevated Temperature
Open this publication in new window or tab >>Al-Si Cast Alloys - Microstructure and Mechanical Properties at Ambient and Elevated Temperature
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Aluminium alloys with Si as the major alloying element form a class of material providing the most significant part of all casting manufactured materials. These alloys have a wide range of applications in the automotive and aerospace industries due to an excellent combination of castability and mechanical properties, as well as good corrosion resistance and wear resistivity. Additions of minor alloying elements such as Cu and Mg improve the mechanical properties and make the alloy responsive to heat treatment. The aim of this work is studying the role of size and morphology of microstructural constituents (e.g SDAS, Si-particles and intermetalics) on mechanical properties of Al-Si based casting alloy at room temperatures up to 500 ºC.

The cooling rate controls the secondary dendrite arm spacing (SDAS), size and distribution of secondary phases. As SDAS becomes smaller, porosity and second phase constituents are dispersed more finely and evenly. This refinement of the microstructure leads to substantial improvement in tensile properties (e.g. Rm and εF). Addition of about 280 ppm Sr to EN AC- 46000 alloy yields fully modified Si-particles (from coarse plates to fine fibres) regardless of the cooling conditions. Depression in eutectic growth temperature as a result of Sr addition was found to be strongly correlated to the level of modification irrespective of coarseness of microstructure. Modification treatment can improve elongation to failure to a great extent as long as the intermetallic compounds are refined in size.

Above 300 ºC, tensile strength, Rp0.2 and Rm, of EN AC-46000 alloys are dramatically degraded while the ductility was increased. The fine microstructure (SDAS 10 μm) has superior Rm and ductility compared to the coarse microstructure (SDAS 25 μm) at all test temperature (from room to 500 ºC). Concentration of solutes (e.g. Cu and Mg) in the dendrites increases at 300 ºC and above where Rp0.2 monotonically decreased. The brittleness of the alloy below 300 ºC was related to accumulation of a high volume fraction damaged particles such as Cu- Fe-bearing phases and Si-particles. The initiation rate of damage in the coarse particles was significantly higher, which enhances the probability of failure and decreasing both Rm and εF compared to the fine microstructure. A physically-based model was adapted, improved and validated in order to predict the flow stress behaviour of EN AC- 46000 cast alloys at room temperature up to 400 ºC for various microstructures. 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. p. 76
Series
JTH Dissertation Series ; 07
Keywords
Al-Si based casting alloys, elevated temperature, microstructural scale effect, Sr modification
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-26805 (URN)978-91-87289-08-8 (ISBN)
Presentation
2015-06-05, E1405, School of Engineering, Gjuterigatan 5, Jönköping, 10:00 (English)
Opponent
Supervisors
Funder
Knowledge Foundation
Available from: 2015-06-22 Created: 2015-05-28 Last updated: 2015-06-22Bibliographically approved
2. 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. p. 66
Series
JTH Dissertation Series ; 21
Keywords
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, SalemEW Jarfors, Anders

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