Influence of the homogenization treatment on the precipitation and dissolution of intermetallic phases and effects on extrudability in direct chilled Al-Mg-Si alloys

Alexander Christoph Wimmer

Research output: ThesisDiploma Thesis

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Abstract

Because of the good strength/density ratio of Aluminium it is widely used in automotive industry. During production and extrusion, the mechanical properties should be quiet low to reduce the demand of deformation force and deformation energy. In the final product, the mechanical properties should fulfil all demands. To meet all requirements, an intelligent design of microstructure (grain size, precipitations, morphology, etc.) is necessary. After casting of the billets the microstructure of the billets is dendritic. Between the dendritic arms are coarse precipitates of an Mg/Si phase (π-phase or a Mg2Si phase) and an plate-like AlFeSi phase. Therefore it is necessary to submit the billets to a heat treatment. The first target of this treatment, which is called homogenization, is to transform the brittle, platelet like brittle AlFeSi phase (which can cause cracks during extrusion) into a pearl-necklace shaped, ductile AlFeSi phase. The second aim is to dissolve the coarse Mg/Si phase which should be precipitated in nanoscale sized particles of Mg2Si which increase the strength of the final product. The main aim of this work is to get a taylor-shaped microstructure to get on the one side good extrudability, which means low extrusion pressure, high extrusion speed and an absence of surface defects. On the other hand, the mechanical properties of the extruded profile should meet all requirements of the standards and customers. Through this work the extrusion pressure was reduced significant.
Translated title of the contributionStrangpressbarkeit von Al-Mg-Si Legierungen in Abhängigkeit von Wärmebehandlung und intermetallischen Phasen
Original languageEnglish
QualificationDipl.-Ing.
Supervisors/Advisors
  • Schumacher, Peter, Supervisor (internal)
  • Wöß, Alexander Wolfgang, Supervisor (external), External person
Award date1 Jul 2011
Publication statusPublished - 2011

Bibliographical note

embargoed until 30-05-2014

Keywords

  • intermetallic phases
  • 6082
  • Al-Mg-Si
  • extrudability
  • homogenization
  • precipitations
  • TEM
  • SEM

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