TY - THES

T1 - Influence of the homogenization treatment on the precipitation and dissolution of intermetallic phases and effects on extrudability in direct chilled Al-Mg-Si alloys

AU - Wimmer, Alexander Christoph

N1 - embargoed until 30-05-2014

PY - 2011

Y1 - 2011

N2 - 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.

AB - 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.

KW - intermetallic phases

KW - 6082

KW - Al-Mg-Si

KW - extrudability

KW - homogenization

KW - precipitations

KW - TEM

KW - SEM

KW - Strangpressen

KW - intermetallische Phasen

KW - Mg2Si

KW - AlFeSi

KW - Homogenisierung

KW - TEM

KW - SEM

KW - EDX

KW - 6082

KW - Al-Mg_Si

M3 - Diploma Thesis

ER -