Yield asymmetry and fracture behavior of Mg–3%Al–1%Zn–(0–1)%Sr alloys extruded at elevated temperatures

Effect of pre-deformation anneal on the microstructure and texture evolution of Mg–3Al–1Zn–0.7Sr alloy during hot extrusion

“…It has been reported by L'Espérance et al [21] that the non-equilibrium Al-Mg-Sr precipitate rejects its excess Mg to the matrix and absorbs Al from the surroundings and decomposes to the equilibrium Mg-Al 4 Sr eutectic. This decomposition has also been seen during the hot deformation of a cast alloy by the authors [15]. The unstable ternary precipitates can be partially or completely decomposed at different annealing times or temperatures.…”

“…Strontium has also been added to work Mg alloys (AZ31 and M1) and the hot deformation behavior has been thoroughly studied [6][7][8][9][10][11][12][13][14][15]. Much work has been produced on the deformation of AZ31 [16][17][18][19] but the literature on AZ31 with Sr is scarce.…”

“…Sr alloys, at specific thermomechanical conditions, thermally stable Al-Sr precipitates are able to initiate particle stimulated nucleation (PSN) and form grains with orientations other than the dominant basal texture [13,14]. Nonetheless, there is an optimum level for Sr addition; excess levels of Sr will make the alloy brittle in deformation by inducing crack initiation at the Al-Sr precipitates [15]. Figure 1 shows how Sr influences the micro-mechanisms involved in the hot extrusion of AZ31-Sr alloys [14].…”

“…Texture measurements reveal the alignment of basal poles with the compression axis (perpendicular to the circular cross section of the extruded bar) and the formation of the basal ring texture in all the samples. However, an increase in the duration of the predeformation anneal switches the plane facing the extrusion direction from first order prismatic (10-10) to second order prismatic planes (11)(12)(13)(14)(15)(16)(17)(18)(19)(20). Annealing decreases the Al solute concentration in Mg and lowers the lattice resistance against dislocation movement.…”

“…Annealing decreases the Al solute concentration in Mg and lowers the lattice resistance against dislocation movement. Consequently, the more favorable (0002) [11][12][13][14][15][16][17][18][19][20] slip system is activated in grains that see low basal resolved shear stress (s). As a result, those grains work harden and are consumed by dynamic recrystallization (DRX).…”