Effect of weld parameters on joint quality in friction stir welding of Mg alloy to DP steel dissimilar materials

Dissimilar material joining between magnesium (AZ31B) alloy and dual-phase steel (DP600) was achieved using the friction stir welding (FSW) process. The present work aimed at studying the effect of tool rotational speed and welding speed on the microstructure and mechanical properties of the dissimilar joints. The joints were fabricated at tool rotational speeds of 800 and 1600 rpm with weld speeds of 50, 100, and 150 mm/min, respectively. The plunge depth of 0.2 mm and tool tilt angle of 2 degrees was kept constant during the welding. Temperature rise and variation of torque during the welding process were recorded. Optical microscopy, scanning electron microscopy equipped with energy dispersive spectroscopy (EDS), and X-ray diffraction studies were carried out to understand the microstructural changes, the interface of the weld joints, fracture morphology, and formation of intermetallic compounds during FSW. Maximum joint efficiency of 76.4% was achieved with respect to AZ31B. The microstructural observation revealed the formation of finer grains at the stir zone for all weld parameters because of the dynamic recrystallization. The metallurgical bonding between the dissimilar materials was observed due to the formation of intermetallic compounds. The formation of the sawtooth profile at the joint interface indicated mechanical interlocking between AZ31B Mg alloy and DP600 steel. Though the AZ31B Mg-DP60 0 steel combination is highly immiscible, the present attempts have successfully created the joining, where one of the substrates provides lightweight while the other provides strength. (c) 2021 CIRP.