The effect of 14H LPSO phase on dynamic recrystallization behavior and hot workability of Mg-2.0Zn-0.3Zr-5.8Y alloy

The effects of stacking sequence changes of the close-packed plane in a long period stacking ordered (LPSO) phase on the hot deformation behavior, dynamic recrystallization (DRX) evolution and hot workability of Mg-2.0Zn-0.3Zr-5.8Y alloy were investigated by compression test. A 14H LPSO phase crystal was fabricated by annealing a solidified crystal with a 18R LPSO structure at 500 degrees C for 20 h. Compression experiments were performed in temperature range of 300-500 degrees C and strain rate range of 0.001-1 s(-1) using Gleeble 1500D thermo-mechanical simulator. Based on the regression analysis for the Arrhenius type equation of flow behavior, the apparent average activation energy of deformation was determined as Q=348.4 KJ/mol. The kinetics of DRX evolution is calculated as X-DRX = 1 - exp[-2.1542((epsilon - epsilon(c))/epsilon*)(1.5119)]. The DRX mechanism of the 14H LPSO phase is almost similar to that of the 18R LPSO phase. On comparison of the alloy with 18R LPSO phase, the formation of lamellar 14H LPSO phase in the Mg matrix can delay the DRX and hinder the growth of DRX grains significantly at the same deformation condition. The transformation of 18R LPSO phase to 14H LPSO phase reduced the workability of Mg-2.0Zn-0.3Zr-5.8Y at low deformation temperatures. The processing map exhibits a deformation domain of complete DRX occurring in the temperature range 454-500 degrees C and strain rate range of 0.001-0.01 s(-1), which are the optimum processing parameters. (C) 2014 Elsevier B.V. All rights reserved.