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Surface formation in direct chill (DC) casting of 6082 aluminium alloys
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.ORCID iD: 0000-0002-3622-4247
2016 (English)In: IOP Conference Series: Materials Science and Engineering, Institute of Physics Publishing (IOPP), 2016, Vol. 117, no 1, 012038Conference paper, (Refereed)
Abstract [en]

Surface defects in aluminium billet production are a real problem for the subsequent extrusion procedure. Extrusion productivity can be influenced by the surface properties, which is defined as surface appearance, surface segregation zone depth and large Mg2Si and β-particles (Al5FeSi). In this research the surface formation during DC casting of 6082 aluminium billets produced by the air slip technology is studied. The surface microstructures of 6082 aluminium alloys with smooth and wavy surface appearances were investigated, including segregation zone depths and phase formation. The results were discussed based on the exudation of liquid metal through the mushy zone. The specific appearance of the wavy surface of 6082 alloys was correlated to how the oxide skin adheres to the underlying mushy zone and coupled to the dendritic coherency and surface tension of the skin. The occurrence of different phases at the very surface and in the layer just below was explained by variations in solidification directions and subsequent segregation patterns.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2016. Vol. 117, no 1, 012038
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:miun:diva-29685DOI: 10.1088/1757-899X/117/1/012038Scopus ID: 2-s2.0-84968853364OAI: oai:DiVA.org:miun-29685DiVA: diva2:1057923
Conference
4th International Conference on Advances in Solidification Processes, ICASP 2014, 8 July 2014 through 11 July 2014
Note

Conference Paper

Available from: 2016-12-19 Created: 2016-12-19 Last updated: 2017-02-08Bibliographically approved
In thesis
1. Investigation of Surface Formation in As-Cast and Homogenized 6xxx Aluminium Billets
Open this publication in new window or tab >>Investigation of Surface Formation in As-Cast and Homogenized 6xxx Aluminium Billets
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The direct chill (DC) casting technique to produce billets for extrusion and ingots for rollingwas developed in the 1930s. The principle, which is still valid, is a two-stage cooling with a primary cooling at a mould surface followed by water spraying directly on the surface. Improvements of this technique have mainly focused on changes to the primary cooling, where a water-cooled metal mould has been replaced by different techniques to minimize cooling at this stage. The drive for development comes from the extrusion industry, which can increase the productivity and quality of extruded profiles by improving the billet surface appearance and structure. Hot top casting supported by airflow against the casting surface during the primary cooling is currently the standard procedure to achieve acceptable billet surfaces. The goal is to minimize the depth of the surface segregation zone, which is the governing factor for the appearance of different phases in the surface region. Billet surface quality is evaluated by quantifying surface appearance, segregation zone thickness, and  occurrence of large Mg2Si and β-particles near the surface. The β-Al5FeSi intermetallic phase and coarse Mg2Si particles have negative effects on extrudability and workability of 6xxx Al alloys billets. To achieve extruded products with a high surface quality the as-cast billets are  heat-treated before extrusion. During heat treatment the undesired intermetallic particles, i.e., β-AlFeSi platelets are transformed to rounded α-Al(FeMn)Si intermetallic phases.

In this  research the formation of the surface segregation for smooth defect-free surfaces in both as-cast and homogenized billets was studied. In addition, the surfaces with defects such as wavy, spot and vertical drag defects were investigated and possible mechanisms for initiation of those defects were explained. Moreover, for a better understanding of the homogenization process in-situ studies of the heat treatment of 6082, 6005, 6060 and 6063 Al alloys were carried out by using a transmission electron microscope (TEM). Based on the observations, an explanation of the probable mechanisms taking place during transformation from β-to α-phase was presented.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2017. 52 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 259
Keyword
DC casting, surface segregation, surface defects, intermetallic phase, phase transformation, homogenization
National Category
Engineering and Technology
Identifiers
urn:nbn:se:miun:diva-30007 (URN)978-91-88527-08-0 (ISBN)
Public defence
2017-03-14, O102, Holmgatan 10, 851 70, Sundsvall, 13:15 (English)
Opponent
Supervisors
Note

Vid tidpunkten för disputationen var följande delarbeten opublicerade: delarbete 5 manuskript, delarbete 6 inskickat och delarbete 7 inskickat.

At the time of the doctoral defence the following papers were unpublished: paper 5 manuscript, paper 6 submitted, paper 7 submitted.

Available from: 2017-02-08 Created: 2017-02-08 Last updated: 2017-02-09Bibliographically approved

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