Friction Stud Welding of Dissimilar Metals Applications such as radiators, claddings, and vehicle parts at times require stud welding between dissimilar metals (such as a steel stud and Al plate). Although arc stud welding is extensively used to join similar materials, it is not suitable for joining dissimilar metals because the molten metal cannot be completely extruded out of the joining interface, leading to the presence of brittle intermetallic compounds. In the past ten years, friction stir welding (FSW) (Ref. 1) and friction stir processing (FSP) (Ref. 2) have received much attention as versatile ways to join or process Al in solid state. In addition, TWI has provided a video on friction stud welding of steel stud to steel plate as a novel variant of FSW for joining steels (Ref. 3). Since friction stud welding belongs to the group of solid-state welding techniques such as friction stir welding, it possesses the advantages of disrupting the oxide film and inhibiting excessive growth of the interfacial phase during dissimilar joining. Therefore, friction stud welding may be expected to join dissimilar metals such as aluminum to steel. However, to our knowledge, information on friction stud welding of dissimilar metals has been rarely reported. The work reported in this article investigated the feasibility of friction stud welding of steel stud to Al plate using a traditional milling machine in terms of the joint microstructure feature and fracture behavior. Especially, the formation of a secondary friction interface within 54 JANUARY 2013 the softer Al and the effect of upsetting on eliminating cracks were demonstrated. Experimental Procedure Figure 1 shows a schematic of the friction stud welding process with and without upsetting. The process can be divided into three primary stages: plunging stage, continuous heating stage by friction at plunge depth position (called in situ friction stage), and stopping stage for the rotating motor with or without upsetting action. In the preliminary work, an inexpensive, traditional milling machine without braking and pressure-applying devices was used. Upsetting was achieved by manually lifting the work table with a rotatable handle to stop the rotation of the motor. A 10-mm-diameter, medium-carbon steel bar was used as the stud, and a 1060 Al plate with dimensions of 60 × 23 × 2.8 mm was used as the other base component. Before welding, each surface to be joined was polished with #400 emery paper and then cleaned with acetone. The selected welding parameters were constant, including 1500 rev/min rotation speed, 0.5 mm plunge depth, and 3 s friction time at the plunge position. When upsetting was applied, displacement was controlled to be 0.1 mm, and the resultant upsetting force was measured using the testing device shown in Fig. 2. Moreover, in order to measure the temperature, a thermocouple was placed within the Al plate, ~1.5 mm below the surface. Generally, when applying upsetting, it takes 7 s to completely stop the rotation of the milling machine’s motor without a braking device. After welding, the joints were evaluated by tensile test using the device shown in Fig. 3. The joint microstructures were examined by a VEGAII XMUINCA scanning electron microscope (SEM) equipped with a backscattered electron (BSE) image analysis system, and the interdiffusion behavior at the interface was examined by energy-dispersive X-ray spectroscopy (EDS). GUIFENG ZHANG, WEIMIN JIAO, JIPENG ZHAO, and JIANXUN ZHANG are with State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an, China. A sound friction stud welded joint of steel stud to Al plate was produced using a traditional milling machine BY GUIFENG ZHANG, WEIMIN JIAO, JIPENG ZHAO, AND JIANXUN ZHANG A B C Fig. 1 — Schematic of friction stud welding process with (A–C) and without (A, B) upsetting.
Welding Journal | January 2013
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