<p> Recrystallization of aluminum alloys, which affects their mechanical properties, was examined by a variety of experimental techniques with electrical resistivity (ER) measurements being one of them. In this work, a new method based on in-situ electrical resistivity measurements has been originated and employed for characterization of recrystallization. In contrast to traditional method of resistivity measurements at either room or liquid N2 temperature on isothermally/isochronally heat-treated samples, a new and simpler approach was proposed. In this work, resistivity of a long sample with a small cross section area (usually, 70 x 2 x 0.2 mm3 strips were employed) was continuously measured while the sample was heated from room temperature to 400°C. In this case, there are several independent contributions to electrical resistivity including contributions from lattice vibrations, second-phase particles, presence of solutes and defects, etc. </p> <p> In order to separate precipitation and recrystallization, a new annealing cycle was proposed through thermodynamic modeling. It was demonstrated that for 5xxx AI alloys only contributions from phonons, Pr, and dislocations, pd, were important. By analyzing a temperature dependence of p , it was intended to separate the effect related to a dislocation density, i.e. to a degree of recrystallization. Since Pr >> pd, this effect is elusive. It can only be detected if a robust numerical differentiation is utilized. A novel spline-based method of robust numerical differentiation was developed and employed to reveal these elusive effects from p(T) (or R(T)) profiles. It was shown that a characteristic peak of the d p (T) / dT curves points to onset and end of "events" taking place in AI alloys and that peaks' positions depend on the degree of deformation and amount of alloying additions such as Fe and Mn. The onset and extent of recrystallization seen in the resistivity measurement experiments were confirmed by optical metallography and hardness measurements. Uniformity of deformation in samples was investigated by micro-hardness measurements followed by a detailed statistical analysis to prove that deformation is uniform throughout cross-section of the materials. </p> <p> Results suggested that increasing degree of deformation and alloying additions (Fe and Mn) lower the temperature of onset of recrystallization. In addition, it was observed that kinetics of recrystallization was accelerated by the increasing degree of deformation and alloying additions whereas recrystallized grain size decreases with increasing additions of Fe and Mn in Al-3% Mg alloys. </p> / Thesis / Master of Applied Science (MASc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/21799 |
| Date | 07 1900 |
| Creators | Vajpai, Sanjay |
| Contributors | Malakhov, Dmitri, Materials Science and Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
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