The effects of deformation parameters and cooling rates on the aging behavior of AZ80+0.4%Ce

The extruded AZ80+0.4% Ce magnesium alloy was twisted in the temperature range of 300 - 380 °C by using a Gleeble 3500 thermal simulation test machine with a torsion unit. The deformed cylindrical specimens were cooled at a cooling rate of 10 °C/s or 0.1 °C/s, respectively, and aged at 170 °C. The microstructure analysis results showed that the grain size decreased with increasing specimen radial position from center (SRPC), and that the strong initial basal texture of the extruded magnesium alloy was weakened. Both continuous and discontinuous dynamic recrystallization mechanisms were involved in contributing to the grain refinement for all specimens investigated. And a novel extension twinning induced dynamic recrystallization mechanism was proposed for specimen deformed at 300 °C. For the specimens deformed at 300 °C and 340 °C followed by a slow cooling rate (0.1 °C/s), precipitates of various shapes (β-Mg17Al12), with the dominant precipitates being on the grains boundaries, appeared on the surface section. For specimen deformed at 380 °C, lamellar precipitates (LPS) in the interiors of the grains were predominant. After aging, the LPS still dominated for specimens twisted at 380 °C; however, the LPS gradually decreased with decreasing deformation temperatures from 380 °C to 300 °C. Dynamically precipitated β, especially those decorating the grain boundaries, changed the competition pictures for the LPS and precipitates of other shapes after aging. Interestingly, LPS dominated the areas for the center section of the specimens after aging regardless of deformation temperatures. Low temperature deformation with high SRPC followed by rapid cooling rate increased the micro hardness of the alloy after aging due to refined grain, reduced precipitates size, decreased lamellar spacing as well as strain hardening.