Effect of microstructural feature on the deterioration of tensile properties and vibration fracture resistance of FSW 5052-H34 alloy

In this paper, 5052H34 Al-Mg plates are joined by Friction Stir Welding (FSW) at various rotation speeds ranging from 2000 to 2700 min^-1 to explore the deterioration of tensile and vibration fracture resistance. An average grain size of 16 ± 1 μm could be observed in the stir zone (SZ) at all rotation speeds. The results of tensile and vibration tests which are done transversely in the stir zone verified that the FSW 5052-H34 specimens become significantly different from the base metal, and the deterioration pertains to the microstructural revolution and joining defects. The best condition of FSW specimens for the test of vibration fracture resistance can be acquired when an optimal tool rotation speed (2400 min^-1) is selected to avoid microstructural defects. The deterioration of the material in this study can also be recognized in the existence of heat affected zone (HAZ). On the other hand, vibration fracture resistance can be significantly improved if the crack initiation and propagation through the stir zone of FSW are controlled. That is correlated with the formation of the fine grains through dynamic recrystallization in the vicinity of stir zone.