At the position of Fig. 4(e), because the nugget is composed of columnar austenite and ferrite distributing along the columnar crystal and developed columnar crystal grows from the nugget edge to the faying surface touching each other without existence of phase interface [13], almost all ultrasound enter into the lower plate through nugget. The echo (the first) amplitude of upper plate bottom is the same as that in corona bond, close to the minimum value. Echo (the first) amplitude of lower plate bottom is higher. The distance between peaks is the beam path of two plates. Corresponding main frequency is the same as that in corona bond, still 1 MHz, as shown in Fig. 5(e1) and (e2).