Microstructural evolution during hot shear deformation of an extruded fine-grained Mg–Gd–Y–Zr alloy

Abstract

Abstract:Mg-Gd-Y-Zr alloys are among recently developed Mg alloys having superior mechanical properties at elevated temperatures. Dynamic recrystallization (DRX) and rare earth (RE)-rich particles play important roles in enhancing the high temperature strength of these alloys. Accordingly, the microstructural evolution of a fine grained extruded Mg-5Gd-4Y-0.4Zr alloy was investigated after hot shear deformation in the temperature range of 350-450 °C using the shear punch testing (SPT) method. The results reveal the occurrence of partial dynamic recrystallization at the grain boundaries at 350 °C while the fraction of DRX grains increases with increasing deformation temperature. A fully-recrystallized microstructure was achieved after SPT at 450 °C. The Gd-rich and Y-rich cuboid particles, having typical sizes in the range of ~50 nm to ~3 m, show excellent stability and compatibility after hot shear deformation and these particles enhance the high temperature strength during hot deformation at elevated temperatures. The textural evolution, examined using electron backscattered diffraction (EBSD), revealed a non-fibrous basal DRX texture after SPT which is different from the conventional deformation texture.

Structure, mechanical and corrosion properties of extruded Mg-Nd-Zn, Mg-Y-Zn and Mg-Y-Nd alloys

“…Otherwise, unrecrystallised grains have their basal planes parallel with the extrusion direction. Such texture is generally observed for extruded magnesium alloys [20,24,33,34].…”

“…The elevated temperature is necessary to activate new slipping systems which would allow the plastic deformation. Extrusion at elevated temperature can also be associated with the recrystallisation process if extrusion temperature is above the recrystallisation temperature of the alloy [20]. As a result, a fine-grained microstructure with improved mechanical properties can be obtained [21].…”

Effect of Ag Addition on the Hot Deformation, Constitutive Equations and Processing Maps of a Hot Extruded Mg-Gd-Y Alloy

“…Considering Eqs. [2] to [4], material constants such as n 1 , b can be calculated by obtaining the average slopes of the lines in lnð_ e) vs. ln(r) and ln(_ e) vs. r plots, respectively, and the coefficient a is equal to the ratio of b/n 1 . Furthermore, n, which is the stress exponent of the hyperbolic-sine relationship, can be calculated via the slope of the ln(_ e) vs. the sinh ar ð Þ ½ plot at constant temperatures.…”

“…[3] Conventional magnesium alloys, however, suffer from low strength and low thermal stability at elevated temperature conditions. [4] Consequently, addition of rare earth elements (RE) has been suggested in order to enhance high-temperature properties, e.g., microstructural stability, [5,6] creep resistance [7,8] and strength. [9,10] Among Mg-RE alloys, those based on the Mg-Gd-Y system are prominent for their remarkable high strength because of the solubility of both Gd and Y atoms in magnesium and the presence of thermally stable precipitates with a wide range of varieties.…”