Friction Stir Welding (FSW) is a suitable technology to join dissimilar metals such as aluminum and copper or aluminum and titanium. Since it is a solid state welding process, the solidus temperature is typically not exceeded and the formation of intermetallic phases can be minimized compared to fusion welding processes. However, an intermetallic layer is still formed at the joining interface. This layer determines the seam properties such as the joint strength or the electrical conductivity. The thickness of the layer is in the nanometer range and is mainly influenced by the welding temperature via an Arrhenius law. The process temperature mainly depends on the rotational speed and on the feed rate of the machine tool. In this study, a temperature control system for aluminum-copper lap joints was developed. A PI control system was used for this purpose to maintain the given welding temperature by adjusting the rotational speed. Consequently, a constant welding temperature was ensured along the entire seam and influences such as changes in workpiece geometry, environmental conditions, or material variations could be mitigated. Experiments with six different temperature levels (low – high) were conducted for one exemplary welding task in order to verify the proposed constant welding conditions. The joints were investigated by tensile shear tests as well as optical and electron microscopy. It was proven that temperature-controlled FSW ensures a constant thickness of the intermetallic compound layer.
Friction stir welding is a solid-state welding technology, which is suitable for joining dissimilar metals such as aluminium and copper. Because the solidus temperature is typically not exceeded, the formation of intermetallic phases can be reduced when compared to fusion welding processes. In friction stir welding, the intermetallic layer thickness, which determines the seam properties, is influenced by the welding temperature and is formed in correspondence with the Arrhenius law. It is typically in the range of a few hundred nanometers thick. In turn, the process temperature is determined by the process parameters, primarily the rotational speed and the feed rate of the machine tool. In this study, a temperature-controlled friction stir welding process has been applied to lap joints of aluminium and copper. Welding experiments with various welding speeds and probe lengths were performed in order to assess the effect of the temperature-time profile near the welding interface. The joints were investigated by tensile shear tests as well as optical microscopy and scanning electron microscopy.Friction stir welding of dissimilar metal joints Materialwiss. Werkstofftech. 2019, 50, 949-957
Friction Stir Welding (FSW) is a suitable technology for joining dissimilar materials. As the process temperature during FSW typically does not exceed the solidus temperature, like in fusion welding, high quality joints can be produced with a minimum of intermetallic phases. A comprehensive description of the effective joining mechanisms of friction stir welded dissimilar material joints is still subject of research. In this study the results of an analysis of the effect of the pin length, which is supposed to have a significant influence on the characteristics of the joining mechanisms, are presented. Especially the influence on the bonding conditions and the mechanical properties of the joints has been investigated. For this purpose combinations of aluminum and titanium have been welded with varying pin length at different rotational speeds. The experiments show that at a sufficient distance between the interface zone and the pin tip the bonding is realized by a substance-to-substance bond and microscopic form-fit. As this distance decreases, a visible macroscopic form-fit is generated. However, this macroscopic form-fit causes no significant elevation of the joint strength. First scanning transmission electron microscopy (STEM) images reveal an interfacial layer, which indicates a diffusion of the two materials.
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