Fig. 2 Microcrack started from the top surface of FSW DH36 W1D between steady state and the plunge regions. (a) low magnification, (b) high magnification. The sample was cut in the direction of the weld line

Fig. 2 Microcrack started from the top surface of FSW DH36 W1D between steady state and the plunge regions. (a) low magnification, (b) high
magnification. The sample was cut in the direction of the weld line