Friction stir welding, FSW, of harder metal alloys is difficult to perform, like here dissimilar welding of titanium alloy to stainless steel in butt joint configuration. One major limitation is tool wear which can be reduced by preheating with a laser beam. A mathematical model to calculate the tool forces during FSW was developed further. The calculations show that the laser beam reduces forces at the pin and shoulder of the FSW-tool, accompanied by reduced heat generation through the tool. Within its operating limits, the process has low sensitivity on the lateral position of the leading laser beam. The model supports the understanding and optimisation of the complex interaction zone of forces and heat around the FSW-tool.
The dissimilar joining of aluminum (Al) alloy and steel has become attractive in the automotive sector to achieve lightweight components. However, joining Al to steel using conventional fusion welding processes is difficult because of their widely varying thermo-physical properties and the formation of intermetallic compounds (IMCs) at the Al-Fe joint interface. In the present study, the dissimilar joining of a 2.5 mm thick AA5052-H32 and a 1.4 mm thick DP590 steel sheet was performed using friction stir welding (FSW). Moreover, the effects of the process parameters on the mechanical properties and microstructure of FS welds was investigated. The tensile test results indicated that a higher heat input with increasing rotation speed and decreasing travel speed contributed to a higher tensile strength. The maximum tensile strength of the FS welds was 178 MPa, which exhibited a joint efficiency of approximately 79%. As a result of scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) analysis, a thin interfacial layer of less than 1 μm thickness comprising Fe 4 Al 13 IMC was observed at the dissimilar Al-Fe joint interface.
Welding of thick section butt joints experiences limitations for different techniques. One option is to fill a narrow gap layer by layer with laser melted wire, a laser metal deposition technique where the complexity of a keyhole is avoided. The presented results show that wire addition can enable relatively thick layers. In particular, when electrically preheating the wire the process becomes more energy-efficient and favorable wetting conditions might be achieved. Since the wire was preheated by an electric current conducted through the wire to the workpiece, high speed imaging has shown that the wire tip can occasionally ignite small electric arcs. The wire deposited in the narrow gap also shows a fluctuating but self-stabilizing movement of the tip. Imperfections that have to be avoided are hot cracks, cavities, lack of fusion, and an irregular final weld surface topology. The technique shows high potential.
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