PREDICTING PITTING CORROSION RATE OF WELD NUGGET (STIR ZONE) OF FRICTION STIR WELDED DISSIMILAR JOINTS OF ALUMINIUM – MAGNESIUM ALLOYS
Keywords:
Friction stir welding, Dissimilar joint, Aluminium alloy, Magnesium alloy, Pitting corrosion rate, Response surface methodologyAbstract
Joining of Magnesium (Mg) and Aluminium (Al) alloys by fusion welding processes is very difficult due to formation of intermetallic compounds in weld metal. This problem could be overcome by friction stir welding (FSW) because of solid state welding conditions. However, Al/Mg dissimilar FSW joints are more prone to corrosion attack due to the formation of intercalated microstructure in weld nugget (stir zone). The limitation of low corrosion resistance restricts practical applications of these types of joints. In this investigation, an attempt has been made to develop an empirical relationship to predict the pitting corrosion rate of nugget region of friction stir welded dissimilar joints of AA6061 Al – AZ31B Mg alloys. Three important corrosion test parameters, namely, chloride ion concentration, pH value and exposure time are chosen as input parameters. Three factors, five level, central composite rotatable design matrix is used to minimize the number of experimental conditions. Response surface methodology is used to develop an empirical relationship. The developed relationship can be effectively used to predict the pitting corrosion rate of friction stir welded dissimilar joints of AA6061 Al – AZ31B Mg alloys at 95 % confidence level. The methodology adopted to develop the relationship is presented in this paper.
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