| Dynamic strain aging (DSA) during plastic deformation has been observed in several types of materials such as steel and Ni, Ti, Cu, Al alloys, and its effect on the behavior of materials has been investigated. However, compared with the many extensive studies on the serrated flow in those alloys with fcc and bcc structures, few investigations have been reported about DSA phenomenon occurred in magnesium alloys. Obviously, it is necessary to investigate the dynamic strain aging phenomenon of the extruded AZ81 magnesium alloy for deeply understanding the deformation behavior of magnesium alloys.Through performing tensile tests at different temperatures and strain rates, the influence of temperature and strain rate on the dynamic strain aging behaviors of the extruded AZ81 magnesium alloy was studied. The strain rate sensitivity was obtained. Moreover, the temperatures at which the extruded AZ81 magnesium alloy could exhibit the significant DSA phenomenon were determined. The microstructures of the extruded A81 magnesium alloy after tensile deformation were observed using transmission electron microscope (TEM). And the corresponding mechanism for dynamic strain aging was discussed.The experimental results reveal that at the initial strain rates from 5×10-5s-1 to 1×10-4S-1, the serrated flow is observed for the extruded AZ81 magnesium alloy during tensile deformation at temperatures ranging from 125℃to 200℃. At the strain rate of 5×10-4s-1, the DSA phenomenon is observed at temperatures ranging from 150℃～200℃. Both yield strength and ultimate tensile strength may exhibit the higher values within the temperature ranges where the DSA occurs, while the ductility of the alloy does not decrease significantly. Moreover, the density of the dislocations increases with an increase in temperature, and the interaction of solute atoms with mobile dislocations gets enhanced. The appearance of precipitates can increase the time for the interaction of solute atoms with mobile dislocations, and thus, precipitates can suppress the slip of the dislocations and lead to the occurrence of DSA. Twinning has rather small contribution to the tensile properties of the extruded AZ81 magnesium alloys, but twin boundaries are effective barriers for dislocations slip on the basal plane of the magnesium matrix and can enhance the effect of strain hardening. For the extruded AZ81 magnesium alloy, the physical model of dynamic strain aging follows the "Qian-Xiao-Li" model. It can be determined that the DSA phenomenon only occurs in temperature range of 0.2～0.5Tm. |
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