High Strain Rate Superplasticity in an Al-Li-Mg Alloy Subjected to Equal-Channel Angular Extrusion

Abstract

The superplastic behavior of an Al-4.1%Mg-2.0%Li-0.16%Sc-0.07%Zr alloy (1421 Al) subjected to intense plastic straining by equalchannel angular extrusion (ECAE) was studied in the temperature interval 250-450 • C at strain rates ranging from 1.4 × 10 −5 to 1.4 s −1 . The grain size after ECAE was about 0.8 µm and the fraction of high angle boundaries was about 80 pct. The highest elongation of 1850% without failure appeared at a temperature of 400 • C and initial strain rate of 1.4 × 10 −2 s −1 with corresponding coefficient of the strain rate sensitivity of 0.6. It was shown that the ECAE processed 1421 Al exhibits superior superplastic properties in the temperature range 300-450 • C with the strain rate sensitivity higher than 0.4. Microstructural evolution and cavitation during high strain rate superplastic deformation were examined.

Microstructure and Mechanical Properties of an Al-Li-Mg-Sc-Zr Alloy Subjected to ECAP

“…It was shown previously [31] that ECAP at 300 • C of this alloy provides the formation of the well-defined subgrain structure (ε~2), partially recrystallized structure (ε~4) and fully recrystallized structure (ε~8). The last structure is uniform with an average grain size of~1 µm [2,[29][30][31]; most of the crystallites are true grains entirely outlined by HAGBs. This structure is essentially stable under annealing at a temperature of 450 • C [2,30,32].…”

“…The last structure is uniform with an average grain size of~1 µm [2,[29][30][31]; most of the crystallites are true grains entirely outlined by HAGBs. This structure is essentially stable under annealing at a temperature of 450 • C [2,30,32]. Therefore, this alloy can be subjected to solution treatment followed by quenching with a UFG structure.…”

“…The fourth route of TMP can be applied to materials such as Weldalite (AA2X95) alloy [16], in which normal grain growth took place; increase in grain size under solution treatment is insignificant. Therefore, it is reasonable to apply the fourth route of TMP only to Sc-bearing aluminum alloys, in which coherent Al 3 Sc dispersoids effectively suppress the migration of HAGBs under conditions of solution treatment that retains a UFG structure evolved under prior ECAP [2,29,30]. It was found that a 9% increase in YS of Al-Li alloys processed through this TMP route could be achieved [16].…”

Superplastic Response of an Advanced Al-Li-Mg-Cu-Sc Alloy Subjected to Intense Plastic Deformation

“…It was recently shown [6][7][8] that equal-channel angular extrusion (ECAE) is capable of producing a significant grain refinement in commercial scale rods of aluminum alloys due to occurrence of dynamic recrystallization during intense plastic straining by simple shear. Aluminum alloys subjected to ECAE with large strains could exhibit high superplastic properties.…”

Flat Cavities formed in TZP caused by Superplastic Deformations at High Strain-Rates and Their Effect on Elongation

“…4) However, Primdahl et al 8) showed that such intergranular cracks might be also originated from the volume increase associated with the tetragonal to monoclinic transformation induced in some grains during grinding and polishing processes to a TEM foil. Despite a large number of studies concerning cavitation behaviors in superplastic materials, [3][4][5][6][7][8][10][11][12][13] only a few data -obtained from exactly as-deformed specimens, i.e., without the surface preparation -have been reported so far. It is probable that the surface preparation of specimens before the evaluation of cavitation may give errors in the data.…”