Controlling Interfacial Reaction during Dissimilar Metal Welding of Aluminium Alloys

A critical issue when joining aluminium alloys to dissimilar metals such as magnesium, titanium, and steel is to control the formation of brittle intermetallic compounds (IMCs) that occur due to the reaction at the joint interface. It is demonstrated that once the IMC exceeds a critical thickness, failure of welds always occurs in a brittle manner, with cracks propagating through the IMC. One approach to minimize IMC thickness is to use a solid state joining process, such as friction stir or ultrasonic welding. However, even using these processes, an IMC that exceeds the critical thickness can either form during welding or post-weld heat treatment. In this paper, a number of approaches are discussed to control IMC formation in welds between aluminium alloys and magnesium alloy. Modelling predictions indicate that interfacial reaction rates and grain size of the IMC phases are two critical factors to control layer growth. Experimental results demonstrate that the grain size of IMC layers changes as the layers grow. These modelling predictions and experimental results offer new design strategies to optimize dissimilar metal welding involving aluminium.