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

Table 3

The grain size and the hardness of the copper with different welding conditions.

Condition	Grain size (μm)	Vickers hardness in NZ zone
Base metal	18	79.92
400 rpm	6	100.88
600 rpm	7.5	103.47
900 rpm	9	124.43
1200 rpm	20	121.44
1500 rpm	25	95.3