Alloying- and process-controlled texture and microstructure engineering in aluminum alloys

Jakob Grasserbauer

Research output: ThesisDoctoral Thesis

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Abstract

In recent decades, the usage of aluminum and its alloys has become an essential measure to reduce the CO2 emissions in the automotive sector and to further promote electromobility by compensating the adverse weight increase of the battery-systems. To comply with the changing safety standards, a steady increase in the mechanical properties such as strength is required. In turn, modern car-body design demands enhanced formability of the used materials. As these properties are strongly defined by the microstructures and textures of the Al sheets, the control of those variables enables the desired property combination in optimized Al alloys. The different impacts of the alloying elements in AlMg(Mn) and AlMgSi alloys, frequently used in the automotive industry, exhibit significant alterations in the microstructure and texture evolution throughout common sheet processing. The final sheet's properties are further controlled by various parameters such as the casting cooling rate, the degree of deformation, and the applied heat treatments, which makes sophisticated alloy and process design indispensable for the development of advanced aluminum alloys. As the design of novel alloys or the application of alternative process parameters are initially realized on a laboratory scale, the comparability and transferability of promising results in microstructure and texture formation to the industrial scale is crucial. Therefore, laboratory- and industrial-fabricated sheets of the standard alloys EN AW-5182 and EN AW-6016 are analyzed after fundamental steps throughout the entire processing chain. The results indicate good conformity for the microstructures but reveal discrepancies in the strength of individual texture components especially in the deformed AlMgSi alloys. However, as the final annealed microstructures and textures are comparable, the established laboratory sheet processing has been approved for further microstructure and texture analyses. In consideration of increasing amounts of recycled Al products, the influence of "impurity" elements such as Fe on the microstructure and texture formation of AlMg(Mn) alloys is investigated in a detailed laboratory scale study. The primary and secondary phase volume fraction, size, and composition is altered by various Fe/Mn ratios as well as different process parameters. The experimental results - using various characterization techniques - show good conformity with the performed thermodynamic calculations. The microstructures further indicate both effects of particle stimulated nucleation and Zener pinning, resulting in significant grain refinement for higher Fe and Mn alloying levels. In combination with the highly random textures of the final annealed sheets, the studied Fe and Mn alloyed Al sheets show beneficial microstructural features, which may also positively influence the mechanical properties of the alloys.
Translated title of the contributionLegierungs- und prozessgesteuerte Textur- und Gefügeentwicklung in Aluminiumlegierungen
Original languageEnglish
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Weißensteiner, Irmgard, Co-Supervisor (internal)
  • Pogatscher, Stefan, Supervisor (internal)
  • Uggowitzer, Peter, Assessor A (internal)
  • Clemens, Helmut, Assessor B (internal)
Publication statusPublished - 2021

Bibliographical note

no embargo

Keywords

  • aluminum
  • microstructure
  • texture
  • primary phases
  • secondary phases
  • dispersoids
  • Zener pinning

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