Solid state welding of steel and magnesium alloy using a rotating pin - Solid state welding of dissimilar metals using a rotating pin (report 3)

Authors tried to butt-weld a mild steel plate to a magnesium alloy plate by the solid state welding using a rotating pin. This study investigated the effects of pin rotation speed, the position for the pin axis to be plunged on the strength and the microstructure of the joint. The main results obtained are as follows. Butt-welding of a steel plate to a magnesium alloy plate was easily and successfully achieved. The maximum tensile strength of a joint reached about 70% of the magnesium base metal tensile strength and the fracture path was along the joint interface. When pin rotation was slow, some defects appeared in the magnesium matrix of a joint due to insufficient plasticization of the magnesium. The joint strength increased with the pin rotation speed. This seems to be because the plasticization of the magnesium was increased and the pressure for pushing the plasticized magnesium onto an activated faying surface of the steel was increased. However, the excessive increase of the pin rotation speed caused the ignition of the magnesium, resulting in the decrease of a joint strength. At the pin offset of 0.2mm toward steel, steel fragments scattered in the magnesium matrix in the form of small piece which had no influence on the joint strength. However, larger offsets over 0.2mm made the steel fragment scattering in the magnesium matrix continuous and parallel to the weld interface. Since fracture path tended to occur along the continuous steel fragments perpendicular to the tensile direction, the joint strength decreased.