TY - BOOK

T1 - Optimization of Al-Mg and Al-Mg-Si alloys for cryogenic deformation

AU - Gruber, Belinda

N1 - no embargo

PY - 2020

Y1 - 2020

N2 - The automotive industry is striving for aluminium alloys for lightweight construction with better formability in order to produce more complex components. A possibility to increase the ductility of aluminium is by lowering the forming temperature. The focus of this thesis is to investigate the mechanisms behind cryogenic deformation and to reveal the potential of an optimization of alloys to further enhance this behaviour. Results showed that the increase in strength and ductility is linked with a higher strain hardening rate accompanied by a low dynamic recovery compared to room temperature. This suggests a higher dislocation density at low temperatures, which was confirmed quantitatively via synchrotron experiments. Simultaneously, a change in dislocation character and thus a higher proportion of screw dislocations was detected. Low temperature deformation results also in a more homogeneous dislocation arrangement, shifting the critical dislocation accumulation causing failure to higher elongations and therefore improves formability. Not only the mechanism of the cryogenic forming, but also the influence of subsequent room temperature recovery and artificially ageing on the mechanical properties and the dislocation density was clarified. Recovery processes and the subsequent stability of the cryogenically deformed state are previously unnoticed challenges in further processing or scientific investigations. Hence, knowledge of these effects is crucial to build and develop new industrial processes utilizing cryogenic deformation.

AB - The automotive industry is striving for aluminium alloys for lightweight construction with better formability in order to produce more complex components. A possibility to increase the ductility of aluminium is by lowering the forming temperature. The focus of this thesis is to investigate the mechanisms behind cryogenic deformation and to reveal the potential of an optimization of alloys to further enhance this behaviour. Results showed that the increase in strength and ductility is linked with a higher strain hardening rate accompanied by a low dynamic recovery compared to room temperature. This suggests a higher dislocation density at low temperatures, which was confirmed quantitatively via synchrotron experiments. Simultaneously, a change in dislocation character and thus a higher proportion of screw dislocations was detected. Low temperature deformation results also in a more homogeneous dislocation arrangement, shifting the critical dislocation accumulation causing failure to higher elongations and therefore improves formability. Not only the mechanism of the cryogenic forming, but also the influence of subsequent room temperature recovery and artificially ageing on the mechanical properties and the dislocation density was clarified. Recovery processes and the subsequent stability of the cryogenically deformed state are previously unnoticed challenges in further processing or scientific investigations. Hence, knowledge of these effects is crucial to build and develop new industrial processes utilizing cryogenic deformation.

KW - Aluminium Legierungen

KW - kryogene Temperatur

KW - Versetzungsdichte

KW - Synchrotronstrahlung

KW - Erholung

KW - Aushärtungskinetik

KW - aluminium alloys

KW - cryogenic temperature

KW - dislocation density

KW - synchrotron radiation

KW - recovery

KW - ageing kinetics

M3 - Doctoral Thesis

ER -