Microstructural Response to Hot Working of Mg-4Al-2Ba-1Ca (ABaX421) as Revealed by Processing Map


The hot working mechanisms that occur in ABaX421 alloy have been evaluated using processing maps in the temperature range 300–500 oC and strain rate range 0.0003–10 s-1. The map exhibited two domains in the ranges: (1) 340–480 oC and 0.0003–0.001 s-1 with a peak efficiency of 40% at 420 oC/0.0003 s-1, and (2) 450– 500 oC and 0.003–0.6 s-1 with a peak efficiency of 38% at 500 oC/0.06 s-1. Dynamic recrystallization occurs in both the domains and is caused by basal+prismatic slip and climb in the first domain and by second order pyramidal slip and cross-slip in the second domain. Fine grained microstructures are produced in specimens deformed in both the domains along with ductile fracture in tension, indicating that the alloy has good hot workability. The apparent activation energy values estimated in the Domain 1 and Domain 2 are 211 and 243 kJ/mole, respectively. These values are higher than that for lattice self-diffusion in Mg, indicating that the back stress caused by the intermetallic particles is significant. Also, in the temperature range 300–380 oC at strain rates >0.01 s-1, flow instability occurs in the form of adiabatic shear band and flow localization.
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