Executive Summary : | Ship structures and machinery (predominantly made of steel) continually face the aggressive corrosion challenges from seawater, including salt-laden air, microbial action, corrosive cargoes, and fuels used in primary and auxiliary engines. There have been sincere efforts to mitigate corrosion in marine environments by developing and implementing novel solutions to prevent degradation. However, underwater parts have many challenges to counteract the severe effect of chloride ions in seawater. Besides, the formation of salt-laden dew that contains corrosion-causing chloride ions in the night, followed by temperature gradience in the daytime, aggravates the corrosion. The cathodic protection methodology involves protecting structures at the expense of current (impressed current method) or other material (sacrificial anode method). magnesium alloys are the lightest structural materials and exhibit good anodic characteristics, it is extensively used in sacrificial anode application. Most magnesium alloy-based anodes are made of the Mg-Al-Zn alloy system (Al: 5-7% and Zn: 2.5-3.5%) with an average corrosion potential of -1.55V. However, these magnesium alloys are prone to localized corrosion at a high corrosion rate from a corrosion perspective. This necessitates research in developing magnesium - rare earth based alloys (Mg-RE alloys) with controlled corrosion kinetics for sacrificial anodic applications. Of the many technologies available, compositing technologies enable fine dispersion of new material systems (non-metals or ceramics in micron phase or nanophase as particles or whiskers or fibers) into the matrix of magnesium alloys and hence reduces corrosion rate with no or significantly less compromise on the corrosion potential. The research work proposes to develop surface composites of Mg-RE alloy for sacrificial anodic applications by friction stir processing (FSP) to achieve the following characteristics: • Supply constant cathodic current and maintain the corrosion potential to protect the ship's hull • Self-resist corrosion by seawater for a prolonged period to enhance the service period of anode The research will investigate the influence of FSP parameters (TRS, TTS) on the properties of Mg-RE alloy using statistical regression models. The generated regression models will be utilized to find the optimum process parameters for fabricating defect-free friction stir processed specimens with upgraded mechanical, corrosion, and tribological properties. The surface composite of Mg-RE alloy will be prepared at the optimum level of FSP parameters. |