Cavitation characteristics in AZ31 Mg alloys during LTSP or HSRSP

The cavitation behaviors in heavily extruded fine-grained AZ31 Mg alloys loaded at 200-400 °C and 6 × 10^-4-1 × 10^-2 s^-1 have been analyzed, covering the low temperature or high strain rate superplasticity (LTSP or HSRSP) regimes. Cavities smaller than 2 μm are basically nearly spherical in shape and randomly dispersed in the matrix, suggesting the involvement of diffusion or superplasticity diffusion controlled cavity growth mechanism. In contrast, the larger cavities tend to be elongated with the long axis aligned toward the loading axis, implying the plasticity controlled cavity growth mechanism. However, it is also recognized that coalescence may play an important role in the elongation of cavities. The cavitation in AZ31 Mg appears to be much less severe than those observed in Al based alloys or composites as a result of higher grain boundary diffusion rate, well-defined grain structure with a high volume fraction of high angle grain boundaries, smooth operation of grain boundary sliding, and the absence of second phases in this solution-hardening alloy.