Mechanisms in Joining of Dissimilar Materials using Friction Stir Welding

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Friction Stir Welding (FSW) is an innovative joining technology. The process, which is driven by plas-tic deformation, can be divided into three phases: local plastification, mixture, and consolidation of the material. For this purpose, wear resistant tools are used. Due to the moderate temperatures of the weld seam, which are below the melting temperature of the joining partners, dissimilar materials can be joined. The general proof of principal is already supplied in the literature. Yet, fundamental knowledge about the mechanisms of the joining process as well as the influencing parameters on the joint quality is missing. These missing fundamentals prohibit a stress-related de-sign of a weld seam in FSW. The planned research project aims at the fundamental understanding of the metallographical process-es at the interface layer of FSW-joints of dissimilar materials. Analyses of the joining mechanisms of aluminum-titanium and aluminum-copper joints, which were welded in overlap- and butt-joint configura-tion, were carried out. Therefore, a fundamental knowledge of the joining mechanisms of friction stir welded dissimilar materials can be derived. This is the basis for modeling the (joining)processes at the interface layer of friction stir welded dissimilar joints. The effective joining mechanisms as well as the joint properties should now be made predictable using the gathered knowledge. By implementing a temperature control for the FSW of dissimilar joints, a stationary process behavior can be main-tained. Hence, the formation of the interface layer and the topography can be controlled for the first time. This directly influences the effective joining mechanisms and as a consequence the joint proper-ties. Furthermore, the numerical models of the second project phase have to be adapted and im-proved concerning the changed conditions of the temperature controlled FSW. Hereby, the limits for a robust FSW process for dissimilar materials can be defined. In addition, methods for non-destructive testing are analyzed regarding their ability to detect and quantify the shape of the interface area (interface layer, topography). This allows to verify the desired joint properties without destroying the welds.