[Retracted] Optimum Rotation Speed for the Friction Stir Welding of Pure Copper

Figure 1

Microstructure of the NZ for (a) base metal and for rotation speeds of (b) 400, (c) 600, (d) 900, (e) 1200, and (f) 1500 rpm.

(a)

(b)

(c)

(d)

(e)

(f)