This work presents an investigation into two areas : the development of zinc based brazing alloys for the joining of copper produced by the rapid solidification technique; the study of the development of microstructures in rapidly solidified dilute zinc alloys. A new model has been proposed, based on the present experimental results and the available data from the literature, to account for the ribbon formation mechanism. Within this model ribbon formation in melt spinning is mainly determined by the behaviour of the viscosity in undercooled melts. It has been shown that, contrary to previous studies, the present model can be used to predict the ribbon thickness of both crystalline and amorphous alloys, and the agreement with the measured values is excellent. The development of microstructures in dilute zinc alloys during rapid solidification has been studied by the deliberate addition of impurity elements. Significant differences in structures are observed between the dilute zinc alloys and high purity zinc. The high purity zinc exhibits a strong preferred orientation with the basal plane parallel to the ribbon surface. The severity of this texture markedly reduces with the formation of cellular substructures in dilute zinc alloys. The morphology of the cells depends on the type of impurity elements present. The presence of impurity elements which expand on solidification leads to the development of an eutectic-like structure consisting of regular lamellae. This requires reorientation of the basal plane and instability of the solid liquid interface during solidification. The instability conditions of the planar solid liquid interface during rapid solidification of these alloys have been examined by using the morphological stability criterion. A possible mechanism which accounts for the formation of unusual structures observed in rapidly solidified dilute zinc alloys has been proposed. The observed variety of microstructures of binary Zn-Mg alloys, and the structural transitions across the ribbon thickness have been reported. Comparisons are made between as-cast and rapidly solidified materials and the resulting structures have been described using a growth rate composition map. Rapidly solidified eutectic and hypereutectic alloys show a tendency to form an amorphous phase. A total of more than 50 zinc based alloys have been investigated for the development of brazing filler metal. Alloys have been examined, and their compositions optimized, in terms of their spreading and wetting abilities and brazing performances to obtain a suitable candidate. Based on the experimental results it has been suggested that Zn-Mg alloys could be used for the joining of copper. They exhibit a lower surface tension, a lower density and comparable mechanical properties to high temperature high strength silver based brazing alloys.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:329102 |
| Date | January 1989 |
| Creators | Akdeniz, Mahmut Vedat |
| Publisher | Open University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://oro.open.ac.uk/57270/ |
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