Friction Stir Welding of Fe-15Mn-10Cr-8Ni-4Si Seismic Damping Alloy

Friction stir welding (FSW) was applied to a 10 mm-thick plate for the Fe-15Mn-10Cr-8Ni-4Si seismic damping alloy. A sound FSW joint was obtained successfully without macro-defects such as groove-like defects and tunnel holes. However, small pores with diameters of 1–5 µm were formed owing to the wear of the FSW tool during the FSW. The decrease in the heat input suppressed the tool wear. Consequently, the distribution of small pores was limited to the border of the stir zone at the advancing side under smaller heat input conditions. The stir zone of the FSW specimen produced at 125 rpm showed a higher tensile strength of 759 MPa owing to the grain refinement and the high elongation of 50% compared with the base metal. In addition, the stir zone exhibited a remarkable fatigue life of 9723 cycles. This was higher than that of the base metal (8908 cycles). Grain refinement occurred by discontinuous dynamic recrystallization (DDRX) via high-angle boundary bulging and direct nucleation in the high-dislocation area. The increase in the heat input suppressed the DDRX owing to the promotion of dynamic recovery.