Thermal Stability of an Mg–Nd Alloy Processed by High‐Pressure Torsion

Abstract

The evolution of microstructure, texture, and mechanical properties of an Mg–1.43Nd (wt%) alloy is investigated after processing by high‐pressure torsion at room temperature through five turns and isochronal annealing for 1 h at 150, 250, 350, and 450 °C using electron backscatter diffraction and Vickers microhardness. The alloy exhibits a good thermal stability up to annealing at 250 °C, with mean grain size of ≈0.65 μm. The microhardness shows an initial hardening after annealing at 150 °C and then a subsequent softening. The deformation texture, a basal texture shifted 60° away from the shear direction (SD), is retained during annealing up to 250 °C. In contrast, a basal texture with symmetrical splitting toward SD is developed after annealing at 350 °C. The precipitation sequence and their pinning effects are responsible for the age‐hardening, stabilization of grain size, and the texture modification. The kinetics of grain growth in the Mg–1.43Nd alloy follows two stages depending on the temperature annealing range, with an activation energy of ≈26 kJ mol−1 in the low temperature range of 150–250 °C and ≈147 kJ mol−1 in the high temperature range of 250–450 °C.

Grain growth activation energy of ECAP-processed Mg-Ce alloy: Effect of deformation temperature

“…The present results indicated that the variation of mechanical properties during static recrystallization and grain growth phenomena of the ECAP-processed Mg-0.3Ce alloy are more related to the grain size than the precipitation or dislocations effects. Similar fitting values were reported for a AZ31 alloy (Hv0 = 38 and KH = 42 HV µm -1/2 ) after ECAP processing [6] and for a Mg-1.44Nd (wt.%) alloy (Hv0 = 39 and KH = 43 HV µm -1/2 ) processed by high-pressure torsion [23].…”

“…Such low value was already reported in severely deformed Mg-based alloys [5,23,31]. In the high-temperature range (350-450 °C), the activation energy (120.7 KJ/mol) is close to the bulk diffusion in pure Mg (135 kJ/mol) [30].…”

“…This value is in good agreement with the supposition that the grain growth occurs by lattice self-diffusion process when the microstructure is characterized by large grain size (Figure 2). Two activation energies of 26 and 147 kJ/mol were found for HPT-processed Mg-1.4Nd alloy at temperature ranges of 150-250 °C and 250-450 °C, respectively [23]. The difference in the activation energy at a high-temperature range in comparison with the present work could be explained by the occurrence of precipitation in the Mg-1.4Nd alloy [23].…”

Grain growth activation energy of ECAP-processed Mg-Ce alloy: Effect of deformation temperature

“…The present results indicated that the variation of mechanical properties during static recrystallization and grain growth phenomena of the ECAP-processed Mg-0.3Ce alloy are more related to the grain size than the precipitation or dislocations effects. Similar fitting values were reported for a AZ31 alloy (Hv0 = 38 and KH = 42 HV µm -1/2 ) after ECAP processing [6] and for a Mg-1.44Nd (wt.%) alloy (Hv0 = 39 and KH = 43 HV µm -1/2 ) processed by high-pressure torsion [23].…”

“…Such low value was already reported in severely deformed Mg-based alloys [5,23,31]. In the high-temperature range (350-450 °C), the activation energy (120.7 KJ/mol) is close to the bulk diffusion in pure Mg (135 kJ/mol) [30].…”

“…This value is in good agreement with the supposition that the grain growth occurs by lattice self-diffusion process when the microstructure is characterized by large grain size (Figure 2). Two activation energies of 26 and 147 kJ/mol were found for HPT-processed Mg-1.4Nd alloy at temperature ranges of 150-250 °C and 250-450 °C, respectively [23]. The difference in the activation energy at a high-temperature range in comparison with the present work could be explained by the occurrence of precipitation in the Mg-1.4Nd alloy [23].…”

Texture evolution in high-pressure torsion processing

“…By increasing the annealing temperature to 623 and 723 K, the recrystallization texture changes to a Bfiber with symmetrical splitting towards SD as shown in Figure 37. Similar to the Mg-0.41Dy alloy already cited, the mean grain size of the Mg-1.43Nd alloy remains stable on annealing up to 523 K but there is major grain growth after annealing at 723 K. A change in the precipitation sequence during the annealing treatment and the pinning effect of the precipitates are responsible for the texture and microhardness variations [10]. By performing a comparison between the texture evolution in the Mg-0.41Dy and Mg-1.43Nd alloys, it is observed that the recrystallization texture of Mg-0.41Dy appears more stable than Mg-1.43Nd at a higher annealing temperature of 673 K. This difference is attributed to the occurrence of extensive DRX during HPT processing in the Mg-0.41Dy alloy and less DRX in the Mg-1.43Nd alloy [10,68].…”

“…Similar to the Mg-0.41Dy alloy already cited, the mean grain size of the Mg-1.43Nd alloy remains stable on annealing up to 523 K but there is major grain growth after annealing at 723 K. A change in the precipitation sequence during the annealing treatment and the pinning effect of the precipitates are responsible for the texture and microhardness variations [10]. By performing a comparison between the texture evolution in the Mg-0.41Dy and Mg-1.43Nd alloys, it is observed that the recrystallization texture of Mg-0.41Dy appears more stable than Mg-1.43Nd at a higher annealing temperature of 673 K. This difference is attributed to the occurrence of extensive DRX during HPT processing in the Mg-0.41Dy alloy and less DRX in the Mg-1.43Nd alloy [10,68]. The absence of DRX during conventional deformation processing such as rolling is also found responsible for the modification or weakening of the recrystallization texture in Mgbased alloys [227,228].…”

Grain growth activation energy of ECAP-processed Mg-Ce alloy: Effect of deformation temperature

“…The present results indicated that the variation of mechanical properties during static recrystallization and grain growth phenomena of the ECAP-processed Mg-0.3Ce alloy are more related to the grain size than the precipitation or dislocations effects. Similar fitting values were reported for a AZ31 alloy (Hv0 = 38 and KH = 42 HV µm -1/2 ) after ECAP processing [6] and for a Mg-1.44Nd (wt.%) alloy (Hv0 = 39 and KH = 43 HV µm -1/2 ) processed by high-pressure torsion [23].…”

“…Such low value was already reported in severely deformed Mg-based alloys [5,23,31]. In the high-temperature range (350-450 °C), the activation energy (120.7 KJ/mol) is close to the bulk diffusion in pure Mg (135 kJ/mol) [30].…”

“…This value is in good agreement with the supposition that the grain growth occurs by lattice self-diffusion process when the microstructure is characterized by large grain size (Figure 2). Two activation energies of 26 and 147 kJ/mol were found for HPT-processed Mg-1.4Nd alloy at temperature ranges of 150-250 °C and 250-450 °C, respectively [23]. The difference in the activation energy at a high-temperature range in comparison with the present work could be explained by the occurrence of precipitation in the Mg-1.4Nd alloy [23].…”

Texture evolution in high-pressure torsion processing

“…By increasing the annealing temperature to 623 and 723 K, the recrystallization texture changes to a Bfiber with symmetrical splitting towards SD as shown in Figure 37. Similar to the Mg-0.41Dy alloy already cited, the mean grain size of the Mg-1.43Nd alloy remains stable on annealing up to 523 K but there is major grain growth after annealing at 723 K. A change in the precipitation sequence during the annealing treatment and the pinning effect of the precipitates are responsible for the texture and microhardness variations [10]. By performing a comparison between the texture evolution in the Mg-0.41Dy and Mg-1.43Nd alloys, it is observed that the recrystallization texture of Mg-0.41Dy appears more stable than Mg-1.43Nd at a higher annealing temperature of 673 K. This difference is attributed to the occurrence of extensive DRX during HPT processing in the Mg-0.41Dy alloy and less DRX in the Mg-1.43Nd alloy [10,68].…”

“…Similar to the Mg-0.41Dy alloy already cited, the mean grain size of the Mg-1.43Nd alloy remains stable on annealing up to 523 K but there is major grain growth after annealing at 723 K. A change in the precipitation sequence during the annealing treatment and the pinning effect of the precipitates are responsible for the texture and microhardness variations [10]. By performing a comparison between the texture evolution in the Mg-0.41Dy and Mg-1.43Nd alloys, it is observed that the recrystallization texture of Mg-0.41Dy appears more stable than Mg-1.43Nd at a higher annealing temperature of 673 K. This difference is attributed to the occurrence of extensive DRX during HPT processing in the Mg-0.41Dy alloy and less DRX in the Mg-1.43Nd alloy [10,68]. The absence of DRX during conventional deformation processing such as rolling is also found responsible for the modification or weakening of the recrystallization texture in Mgbased alloys [227,228].…”

Grain growth activation energy of ECAP-processed Mg-Ce alloy: Effect of deformation temperature

“…The present results indicated that the variation of mechanical properties during static recrystallization and grain growth phenomena of the ECAP-processed Mg-0.3Ce alloy are more related to the grain size than the precipitation or dislocations effects. Similar fitting values were reported for a AZ31 alloy (Hv0 = 38 and KH = 42 HV µm -1/2 ) after ECAP processing [6] and for a Mg-1.44Nd (wt.%) alloy (Hv0 = 39 and KH = 43 HV µm -1/2 ) processed by high-pressure torsion [23].…”

“…Such low value was already reported in severely deformed Mg-based alloys [5,23,31]. In the high-temperature range (350-450 °C), the activation energy (120.7 KJ/mol) is close to the bulk diffusion in pure Mg (135 kJ/mol) [30].…”

“…This value is in good agreement with the supposition that the grain growth occurs by lattice self-diffusion process when the microstructure is characterized by large grain size (Figure 2). Two activation energies of 26 and 147 kJ/mol were found for HPT-processed Mg-1.4Nd alloy at temperature ranges of 150-250 °C and 250-450 °C, respectively [23]. The difference in the activation energy at a high-temperature range in comparison with the present work could be explained by the occurrence of precipitation in the Mg-1.4Nd alloy [23].…”

Texture evolution in high-pressure torsion processing

“…By increasing the annealing temperature to 623 and 723 K, the recrystallization texture changes to a Bfiber with symmetrical splitting towards SD as shown in Figure 37. Similar to the Mg-0.41Dy alloy already cited, the mean grain size of the Mg-1.43Nd alloy remains stable on annealing up to 523 K but there is major grain growth after annealing at 723 K. A change in the precipitation sequence during the annealing treatment and the pinning effect of the precipitates are responsible for the texture and microhardness variations [10]. By performing a comparison between the texture evolution in the Mg-0.41Dy and Mg-1.43Nd alloys, it is observed that the recrystallization texture of Mg-0.41Dy appears more stable than Mg-1.43Nd at a higher annealing temperature of 673 K. This difference is attributed to the occurrence of extensive DRX during HPT processing in the Mg-0.41Dy alloy and less DRX in the Mg-1.43Nd alloy [10,68].…”

“…Similar to the Mg-0.41Dy alloy already cited, the mean grain size of the Mg-1.43Nd alloy remains stable on annealing up to 523 K but there is major grain growth after annealing at 723 K. A change in the precipitation sequence during the annealing treatment and the pinning effect of the precipitates are responsible for the texture and microhardness variations [10]. By performing a comparison between the texture evolution in the Mg-0.41Dy and Mg-1.43Nd alloys, it is observed that the recrystallization texture of Mg-0.41Dy appears more stable than Mg-1.43Nd at a higher annealing temperature of 673 K. This difference is attributed to the occurrence of extensive DRX during HPT processing in the Mg-0.41Dy alloy and less DRX in the Mg-1.43Nd alloy [10,68]. The absence of DRX during conventional deformation processing such as rolling is also found responsible for the modification or weakening of the recrystallization texture in Mgbased alloys [227,228].…”