Pre-Treated Effect of Friction Stir Processing of Al Alloy 5052 on Vibration Fracture Behavior under Resonant Vibration

In this study, 5052 Al–Mg alloy was pre-treated and friction stir processing (FSP) was then performed on the specimens to explore the deformation resistance. The experimental results indicate that the FSP specimens not only had better tensile properties but also better vibration fracture resistance. It is significant that the tensile elongation and deformation resistance tended to increase as the grain was refined by friction stir processing. Results show that the use of FSP yielded uniform hardness distribution and slightly larger n values which improved the vibration fracture resistance of the specimens. However, even without FSP, more uniform elongation and larger n values could still improve the vibration fracture resistance of the specimens. Consequently, the uniform elongation and larger n values play an important role in increasing vibration fracture resistance. As for crack propagation, the FSP specimens revealed only a few slip bands in the vicinity of the main crack, and the 5052H34 specimen displayed a few slip bands in the vicinity of the main crack. However, more slip bands were observed in the vicinity of the main crack on the 5052-O specimens, and there were deformation traces and advancing cracks rising at the front of the main crack. Consequently, vibration fracture resistance can also be better improved if the crack initiation and propagation through the stir zone of FSP specimens are controlled. This is correlated with the formation of fine grains through dynamic recrystallization in the vicinity of stir zone.