A. Chakkedath

In situ analysis of the tensile deformation mechanisms in extruded Mg-1Mn-1Nd (wt%)

An extruded Mg–1Mn–1Nd (wt%) (MN11) alloy was tested in tension in an SEM at temperatures of 323 K (50°C), 423 K (150°C), and 523 K (250°C) to analyse the local deformation mechanisms through in situ observations. Electron backscatter diffraction was performed before and after the deformation. It was found that the tensile strength decreased with increasing temperature, and the relative activity of different twinning and slip systems was quantified. At 323 K (50°C), extension twinning, basal, prismatic ⟨a⟩, and pyramidal ⟨c + a⟩ slip were active. Much less extension twinning was observed at 423 K (150°C), while basal slip and prismatic ⟨a⟩ slip were dominant and presented similar activities. At 523 K (250°C), twinning was not observed, and basal slip controlled the deformation.

In-Situ Study of the Tensile Deformation and Fracture Modes in Peak-Aged Cast Mg-11Y-5Gd-2Zn-0.5Zr (Weight Percent)

Tensile deformation and fracture modes in peak-aged cast Mg-11Y-5Gd-2Zn-0.5Zr (wt pct) (WGZ1152) samples at temperatures between 298 K [25 °C, room temperature (RT)] and 623 K (350 °C) (0.33 to 0.69Tm) were studied in situ inside a scanning electron microscope (SEM) using electron backscatter diffraction (EBSD) and slip trace analysis. The ultimate tensile strength (UTS) (265 MPa) and yield strength (YS) (193 MPa) at 523 K (250 °C) were 91 and 80 pct of those at RT, respectively. The observed dominant slip mode transitioned from basal 〈a〉 slip (100 pct) to basal 〈a〉 slip (81 pct) combined with prismatic 〈a〉 slip (12 pct) from RT to 473 K (200 °C). As the temperature increased to 623 K (350 °C), basal 〈a〉 slip (67 pct) and pyramidal 〈c+a〉 slip (25 pct) became the dominant slip modes. The estimated critical resolved shear stress (CRSS) ratio of pyramidal 〈c+a〉 slip/basal 〈a〉 slip (7.3) was lower than that of prismatic 〈a〉 slip/basal 〈a〉 slip (12.7) at temperatures above 573 K (300 °C). Prismatic 〈a〉 slip and pyramidal 〈c+a〉 slip were more active at higher strains for moderate temperatures [473 K to 523 K (200 °C to 250 °C)] and at high temperatures [573 K to 623 K (300 °C to 350 °C)], respectively. A transition in the dominant fracture mode occurred from transgranular cracking (40 pct) combined with intergranular cracking (60 pct) to intergranular cracking as temperatures increased from RT to 623 K (350 °C). The intergranular crack nucleation sites tended to be located at grain boundaries and the interface between the Mg matrix and the large intermetallic grain boundary X phase. Slip bands were associated with transgranular crack nucleation.

The Deformation Behavior, Microstructure and Mechanical Properties of Cast and Extruded Mg-1Mn-xNd (wt%) at Temperatures between 50°C and 250°C

The tensile deformation behavior of as-cast and cast-then-extruded Mg-1Mn-1Nd(wt%) and Mg-1Mn-0.3Nd(wt%) alloys was studied by performing in-situ tests inside a SEM. A slip/twin trace analysis technique was used to identify the distribution of the deformation systems. Cast-then-extruded Mg-1Mn-1Nd(wt%) exhibited superior elevated-temperature strength retention compared to cast-then-extruded Mg-1Mn-0.3Nd(wt%). Basal slip and extension twinning were observed in the as-cast Mg-1Mn-1Nd(wt%) and Mg-1Mn-0.4Nd(wt%) alloys deformed at 50°C. In cast-then-extruded Mg-1Mn-1Nd(wt%), basal slip, prismatic slip, and pyramidal slip were active at all temperatures. In cast-then-extruded Mg-1Mn-0.3Nd(wt%), at lower temperatures, twinning dominated the deformation and no non-basal slip activity was observed. The extent of twinning decreased with increasing temperature and basal slip was the major deformation mode at 150–250°C in both cast-then-extruded materials. The estimated CRSS ratio of extension twinning with respect to basal slip in Mg-1Mn-1Nd(wt%) was close to unity, suggesting that the addition of Nd results in an increase in the CRSS of basal slip.

In-situ EBSD observations of recrystallization and texture evolution in rolled Mg-2Zn-xCe (wt.%)

Wrought magnesium (Mg) alloys are attractive for automotive applications where light-weighting is critical. One of the major challenges with conventional Mg alloys, such as Mg-3Al-1Zn(wt.%), is the strong texture formation after rolling and subsequent annealing, which results in anisotropic mechanical properties and poor cold formability [1]. It was observed that relatively weak texture can be obtained by dilute rare-earth additions such as Ce [2]. However, the mechanisms responsible for the weak texture formation during annealing are not clear. The goal of this study was to investigate recrystallization and texture evolution during annealing in a Ce containing Mg alloy system using in-situ techniques.