High Strain Rate and/or Low Temperature Superplasticity in AZ31 Mg Alloys Processed by Simple High-Ratio Extrusion Methods

Abstract

There have been numerous efforts in processing metallic alloys into fine-grained materials, so as to exhibit high strain rate superplasticity (HSRSP) and/or low temperature superplasticity (LTSP). The current study applied the most simple and feasible one-step extrusion method on the commercial AZ31 magnesium ingot to result in HSR&LTSP. The one-step extrusion was undertaken using a high extrusion ratio at 250-350 • C, and the grain size after one-step extrusion became ∼ 1-4 µm. The processed AZ31 plate exhibited satisfactory room temperature tensile elongation of 30-50%; 200 • C elongations of 600% at 1 × 10 −4 s −1 and 425% at 1 × 10 −3 s −1 ; and 300 • C elongations of 900% at 1 × 10 −4 s −1 , 520% at 8 × 10 −3 s −1 , 300% at 2 × 10 −2 s −1 , and 210% at 1 × 10 −1 s −1 . This suggests that the current AZ31 Mg alloy has possessed HSRSP at relatively low temperatures of 280-300 • C, as well as LTSP at 200 • C. The low flow stress of 15-30 MPa and the true strain rate sensitivity of 0.3-0.4 both suggest that grain boundary sliding and solute drag creep have operated under these loading conditions. The current results imply that the simple high-ratio extrusion method might be a feasible processing mean for industry applications.

Using Multiple FSP Passes to Cure Onion Splitting of Mg Alloys Deformed at Elevated Temperatures

“…It will be demonstrated below that the lack of satisfactory superplasticity is due to the premature failure as a result of onion splitting. In our previous research results for the similar Mg alloys [21][22][23][24] which have been subjected to severe extrusion (with reduction ratio over 100 : 1) or equal channel angular pressing (6 or 8 passes) to result in a grain size less than 10 mm, the superplasticity elongations were much higher, and even exhibiting the low temperature superplasticity (LTSP) or high strain rate superplasticity (HSRSP) behavior. In contrast, the current one-pass FSP modified Mg alloys with a grain size of 3-8 mm could not perform the comparable superplasiticy.…”

Strengthening and Toughness of AZ61 Mg with Nano SiO<SUB>2</SUB> Particles

“…15) For the current fully recrystallized and fine- grained AZ61 alloys or composites after hot extrusion, the texture intensity was seen to be weak 16) so that M is taken to be around 3. The first row in Table 5 lists the predicted YS values attributed by the Orowan strengthening, i.e., o ¼ o2 Â 3.…”

“…The Hall-Petch relationship for the AZ-series Mg alloys has been established, based on massive experimental data, as ys ¼ 56 þ 348d À1=2 (in units of MPa and mm, respectively). 16) The calculated grain size strengthening values, HP , for various composites possessing different grain sizes are also listed in Table 5.…”

Secondary Processing of AZ31 Magnesium Alloy Concomitant with Grain Growth or Dynamic Recrystallization

“…8(b). 47,51) It is obvious from Fig. 8(a) that either grain coarsening or grain refinement is occurring during deformation.…”