Date: May 2016
Creator: Nelaturu, Phalgun
Description: Metal fatigue is a recurring problem for metallurgists and materials engineers, especially in structural applications. It has been responsible for many disastrous accidents and tragedies in history. Understanding the micro-mechanisms during cyclic deformation and combating fatigue failure has remained a grand challenge. Environmental effects, like temperature or a corrosive medium, further worsen and complicate the problem. Ultimate design against fatigue must come from a materials perspective with a fundamental understanding of the interaction of microstructural features with dislocations, under the influence of stress, temperature, and other factors. This research endeavors to contribute to the current understanding of the fatigue failure mechanisms. Cast aluminum alloys are susceptible to fatigue failure due to the presence of defects in the microstructure like casting porosities, non-metallic inclusions, non-uniform distribution of secondary phases, etc. Friction stir processing (FSP), an emerging solid state processing technique, is an effective tool to refine and homogenize the cast microstructure of an alloy. In this work, the effect of FSP on the microstructure of an A356 cast aluminum alloy, and the resulting effect on its tensile and fatigue behavior have been studied. The main focus is on crack initiation and propagation mechanisms, and how stage I and stage II cracks ...
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