TY - THES

T1 - Microstructural evolution during SPD of AlCu3

AU - Faller, Michael Josef

N1 - embargoed until null

PY - 2010

Y1 - 2010

N2 - By severe plastic deformation (SPD) ultra-fine-grained (UFG) materials can be produced. Because of their extraordinary mechanical and physical properties such materials are of scientific interest and promising for future technical applications. Of all established SPD techniques high-pressure-torsion (HPT) offers the major deformation potential and the feasibility of a saturation in structural refinement. In SPD-processed single-phase metals the occurring UFG microstructures are thermally not very stable. SPD deformed metal-matrix composites show enhanced structural refinement and thermal stability. Age-hardening alloys can be seen as chemical composite materials. By sufficient heat treatments various phases can be introduced, which may influence the limit of refinement and stabilize the occurring microstructure. In this work an age-hardening Al-3wt\%Cu model alloy was studied, to get a better understanding of the phenomena in age-hardening alloys during and after SPD. Samples were heattreated to different material conditions and HPT deformed at various temperatures. During deformation the torque was recorded and HPT-deformed specimens were subsequently aged. The mechanical properties were characterised by micro-hardness measurements and the occurring microstructures were investigated by scanning electron microscopy and transmission electron microscopy. By HPT-processing the investigated Al-Cu alloy an UFG structure was obtained. During deformation the hardening precipitates are disrupted and possibly dissolved. The resulting microstructure consists of mainly high-angle grain boundaries with incoherent grain-boundary precipitates. SPD up to very high strain possibly leads to a structure independent from the initial material condition. The grain-size increases with increasing deformation temperature and decreases with decreasing particle size of the second phase. According to the Hall-Petch relation the strength of the deformed material is mainly governed by the grain size. When aging the deformed material, hardening phases could not be found. Only the incoherent grain boundary precipitates were found to grow, supposedly by interfacial diffusion of copper. Grain-growth during aging seems to be limited by the grain boundary precipitates.

AB - By severe plastic deformation (SPD) ultra-fine-grained (UFG) materials can be produced. Because of their extraordinary mechanical and physical properties such materials are of scientific interest and promising for future technical applications. Of all established SPD techniques high-pressure-torsion (HPT) offers the major deformation potential and the feasibility of a saturation in structural refinement. In SPD-processed single-phase metals the occurring UFG microstructures are thermally not very stable. SPD deformed metal-matrix composites show enhanced structural refinement and thermal stability. Age-hardening alloys can be seen as chemical composite materials. By sufficient heat treatments various phases can be introduced, which may influence the limit of refinement and stabilize the occurring microstructure. In this work an age-hardening Al-3wt\%Cu model alloy was studied, to get a better understanding of the phenomena in age-hardening alloys during and after SPD. Samples were heattreated to different material conditions and HPT deformed at various temperatures. During deformation the torque was recorded and HPT-deformed specimens were subsequently aged. The mechanical properties were characterised by micro-hardness measurements and the occurring microstructures were investigated by scanning electron microscopy and transmission electron microscopy. By HPT-processing the investigated Al-Cu alloy an UFG structure was obtained. During deformation the hardening precipitates are disrupted and possibly dissolved. The resulting microstructure consists of mainly high-angle grain boundaries with incoherent grain-boundary precipitates. SPD up to very high strain possibly leads to a structure independent from the initial material condition. The grain-size increases with increasing deformation temperature and decreases with decreasing particle size of the second phase. According to the Hall-Petch relation the strength of the deformed material is mainly governed by the grain size. When aging the deformed material, hardening phases could not be found. Only the incoherent grain boundary precipitates were found to grow, supposedly by interfacial diffusion of copper. Grain-growth during aging seems to be limited by the grain boundary precipitates.

KW - Severe plastic deformation

KW - HPT

KW - Ultrafine-grained materials

KW - Nanocrystalline materials

KW - Aluminum alloy

KW - Agehardening

KW - Hochverformung

KW - HPT

KW - ultrafeinkörnige Materialien

KW - nanokristalline Materialien

KW - Aluminiumlegierung

KW - Ausscheidungshärtung

M3 - Diploma Thesis

ER -