The correlation between the recrystallization texture and subsequent isothermal grain growth in a friction stir processed rare earth containing magnesium alloy

This study was conducted to examine the correlation between the microstructure and textural evolution and isothermal grain growth behavior of a friction stir processed Mg-Y-RE magnesium alloy. To this end, the friction stir processing (FSP) was applied under the constant rotational speed of 630 rpm and two traverse speeds of 90 mm/min and 30 mm/min. The continuous dynamic recrystallization (CDRX) was identified as the dominant restoration mechanism. The strong preference of [0001]-Taylor axes in CDRX grains, suggested the significant role of prismatic slip on the lattice rotation during CDRX. The new grains with nearly < 11-20 >//PD orientations and 30 degrees[0001] grain boundaries (GBs) preferentially nucleated in grains with nearly < 10-10 >//PD orientations via CDRX. Consequently, the typical {0001} texture component of FSP-Mg alloys with the single orientation of < 10-10 >//PD was changed to a double orientation of < 10-10 >-< 11-20 >//PD, due to the further development of recrystallization texture in the lower traverse speed. Further, the isothermal grain growth study of the processed materials revealed the growth preference of grains with specific orientations, which have emerged during recrystallization. This was attributed to the formation of high mobile Sigma 13a GBs, as well as their orientations with respect to the shear stress which rendering them favorable for preferred growth and reducing the total energy of system. It was generally observed that the thermal stability of FSPed microstructures during subsequent annealing was depended upon the processing conditions due to the different extent of microstructure and textural developments. These findings create a processing window where microstructure instability or i.e. abnormal grain growth (AGG) could be prevented via manipulating processing parameters.