Predicting Corrosion Rate of Weld Nugget (Stir Zone) of Friction Stir Welded Dissimilar Joints of Aluminium - Magnesium Alloys

Joining of dissimilar alloys such as Aluminium (Al) and Magnesium (Mg) by fusion welding processes was very difficult due to formation of Al12Mg17 intermetallic compounds in fusion zone. However, friction stir welding (FSW) is expected to join dissimilar alloys with adequate joint strength because it is a solid-state process. But the Al/Mg FSW dissimilar joints are more prone to corrosion attack due to intercalated microstructure present 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 corrosion rate of nugget region of friction stir welded dissimilar joints of AA6061 Al - AZ31B Mg alloys. Three important immersion corrosion test parameters, namely, chloride ion concentration, pH value and immersion 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 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.