Intermetallic compound formation at the Interface of Diffusion Bond and Friction Stir Weld of Al/Mg joints

Dissimilar joining of Al5083 to MgAZ31 was performed through friction stir welding (FSW) and diffusion bonding (DB). A constant tool rotation rate of 400 rpm and travel speed of 50 mm/min was used for FSW. The peak temperature of this specimen was raised to maximum of 435°C at the advancing side of the FS weld. Thermal cycle of the FSW specimen showed a distinct plateau at about 430 °C, lasting for about 8 s. At the travel speed of 50 mm/min, the distance corresponding to 8 s is about7mm, which is the pin diameter. The presence of the temperature plateau indicates that the temperature at each thermocouple remained constant as the pin passed it. It further indicates that a eutectic reaction probably occurred, and kept the temperature constant as the pin passed by. The weld had an irregular shaped region in the weld center of DB weld and, having a different microstructure and hardness from the two base materials. The irregular shaped region in DB weld, contained a large volume of intermetallic compound Al12Mg17. The present study suggests that constitutional liquation and solid state diffusion at the interface resulted in the intermetallic compound formation in the weld center.