miun.sePublications
Change search
Refine search result
1 - 9 of 9
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Bayat, Nazlin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. Mid Sweden University.
    Investigation of Surface Formation in As-Cast and Homogenized 6xxx Aluminium Billets2017Doctoral 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of this technique have mainly focused on changes to the primary cooling, where a water-cooled metal mould has been replaced by different techniques to minimize cooling at this stage.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.

  • 2.
    Bayat, Nazlin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Carlberg, T.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    On Liquid Metal Wetting of Casting Rings for DC Casting2015In: Light Metals 2015 / [ed] Hyland, M., Wiley-Blackwell, 2015, p. 855-863Chapter in book (Refereed)
    Abstract [en]

    During air-slip direct chill casting of aluminum alloys, uneven or low air pressure areas at the surface of the porous graphite ring mold, can cause the metal to stick to the graphite ring and produce traces along the billets called vertical drags (VD). To prevent this type of defect, it would be an advantage to decrease the wettability of the graphite ring. It has been shown that nanostructured surfaces can have hydrophobic properties, and a question is whether the same effect can be achieved for molten metals. A Ti02 nanowire structure is proposed to cover the casting ring, and the wetting behavior of such a structure has been studied, and compared to the wetting at a regular graphite ring surface by the dispensed sessile drop method. The results showed that the nanostructured surface very strongly de-wets metal droplets.

  • 3.
    Bayat, Nazlin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Carlberg, Torbjörn
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Influence of Heat Treatment on the Surface Structure of 6082 Al Alloys2017In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48A, no 10, p. 5085-5094Article in journal (Other academic)
    Abstract [en]

    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. Although the heat treatment of the bulk areas of the 6xxx Al alloys has been the focus of many previous studies, the process of phase transformation at the very surface has not been paid the same attention. In this study, microstructures of a homogenized billet of a 6082 alloy at the area very close to the surface were investigated. By comparing the X-ray diffraction patterns (XRD) of heat-treated samples as a function of different holding times, the gradual phase transformations could be followed, and using GDOES and map analysis by EDX, the alloying elemental redistribution was analyzed. Partial remelting and porosity growth was detected, and transformation rates were faster than in bulk material and from what is known from industrial processes.

  • 4.
    Bayat, Nazlin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Carlberg, Torbjörn
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    On Liquid Metal Wetting of Casting Rings for DC Casting2015In: TMS Light Metals / [ed] Margaret Hyland, Warrendale: Minerals, Metals & Materials Society, 2015, Vol. 2015-January, p. 859-864Conference paper (Refereed)
    Abstract [en]

    During air–slip direct chill casting of aluminum alloys, uneven or low air pressure areas at the surface of the porous graphite ring mold, can cause the metal to stick to the graphite ring and produce traces along the billets called vertical drags (VD). To prevent this type of defect, it would be an advantage to decrease the wettability of the graphite ring.  It has been shown that nanostructured surfaces can have hydrophobic properties, and a question is weather the same effect can be achieved for molten metals. A TiO2 nanowire structure is proposed to cover the casting ring, and the wetting behavior of such a structure has been studied, and compared to the wetting at a regular graphite ring surface by the dispensed sessile drop method. The results showed that the nanostructured surface very strongly dewetting metal droplets.

  • 5.
    Bayat, Nazlin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Carlberg, Torbjörn
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Surface formation in direct chill (DC) casting of 6082 aluminium alloys2016In: IOP Conference Series: Materials Science and Engineering, Institute of Physics Publishing (IOPP), 2016, Vol. 117, no 1, article id 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.

  • 6.
    Bayat, Nazlin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Carlberg, Torbjörn
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Surface structure formation in direct chill (DC) casting of al alloys2014In: JOM: The Member Journal of TMS, ISSN 1047-4838, E-ISSN 1543-1851, Vol. 66, no 5, p. 700-710Article in journal (Refereed)
    Abstract [en]

    The aim of this study is to increase the understanding of the surface zone formation during direct chill (DC) casting of aluminum billets produced by the air slip technology. The depth of the shell zone, with compositions deviating from the bulk, is of large importance for the subsequent extrusion productivity and quality of final products. The surface microstructures of 6060 and 6005 aluminum alloys in three different surface appearances - defect free, wavy surface, and spot defects - were studied. The surface microstructures and outer appearance, segregation depth, and phase formation were investigated for the mentioned cases. The results were discussed and explained based on the exudation of liquid metal through the mushy zone and the fact that the exudated liquid is contained within a surface oxide skin. Outward solidification in the surface layer was quantitatively analyzed, and the oxide skin movements explained meniscus line formation. Phases forming at different positions in the segregation zone were analyzed and coupled to a cellular solidification in the exudated layer.

  • 7.
    Bayat, Nazlin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Carlberg, Torbjörn
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Cieslar, M.
    Faculty of Mathematic and Physics, Charles University, Prague, Czech Republic.
    In-Situ Study of Phase Transformations during Homogenization of 6005 and 6082 Al Alloys2017In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 725, p. 504-509Article in journal (Refereed)
    Abstract [en]

    Intermetallic β-Al5FeSi phase and coarse Mg2Si particles have negative effects on extrudability and workability of 6xxx Al alloy billets. To achieve extruded products with a high surface quality as-cast billets are therefore heat-treated before extrusion. During heat treatment the undesired intermetallic particles, i.e., β-AlFeSi platelets, are transformed to a rounded α-Al(FeMn)Si intermetallic phase. This transformation was studied in-situ by TEM for 6005 and 6082 Al alloys. It was observed that the Mg2Si particles precipitate in the Al matrix at about 250 °C; this precipitation also occurred at the edge and faces of beta intermetallic particles, and the Mg2Si particles were the preferred sites for α-Al(FeMn)Si particle nucleation. The transformation proceeded faster and at lower temperatures, 350–450 °C, than what has been reported earlier for homogenization studies of bulk samples and industrial billets. This could be associated with the thin characteristic of used samples in TEM giving contribution from fast surface diffusion, but it was also concluded that the phase boundary layer diffusion was important for the understanding of how the transformations proceed.

  • 8.
    Bayat, Nazlin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Carlberg, Torbjörn
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Cieslar, M.
    Charles University, Prague, Czech Republic.
    In-Situ Study of Phase Transformations during Homogenization of 6060 and 6063 Al Alloys2019In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 130, p. 165-171Article in journal (Refereed)
  • 9.
    Carlberg, Torbjörn
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Bayat, Nazlin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Erdegren, Mikael
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Surface Segregation and Surface Defect Formation During Aluminum Billet Casting2015In: Transactions of the Indian Institute of Metals, ISSN 0972-2815, E-ISSN 0975-1645, Vol. 68, no 6, p. 1065-1069Article in journal (Refereed)
    Abstract [en]

    In this paper the surface zone formation during direct chill casting of aluminum billets, produced by the air slip technology, is discussed. The shell zone depth and compositions have been quantitatively studied, and the surface microstructures of 6060, 6005 and 6082 alloys are compared and coupled to surface appearances. The understanding of the results is based on the exudation of liquid metal through the mushy zone and the fact that the exudate liquid is contained within a surface oxide skin, and the oxide skin movements are coupled to various surface appearances. The major defects that occur during billet castings are different kinds of vertical drags or horizontal bandings, also called lapping. The structures coupled to these defects and theories for their formation are discussed.

1 - 9 of 9
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf