The Influence of Thermomechanical Processing Variables on Superplasticity in a High-Mg, Al-Mg Alloy

The superplastic response of an Al-10.2 pct Mg-0.52 pct Mn alloy, warm rolled at 573 K (300 °C), may be enhanced by annealing at a lower temperature, 473 K (200 °C), prior to subsequent stressstrain testing at a warm temperature,e.g., 573 K (300 °C). This enhancement is attributed to recovery and precipitation during annealing effectively retarding continuous recrystallization and growth during subsequent deformation. The finer resultant structure more readily sustains superplastic flow processes. The warm-rolled structure, a refined subgrain structure in conjunction with fine β (Mg5Al8) and MnAl6 precipitates, will statically recrystallize only upon heating to a temperature above the Mg solvus, such as 713 K (440 °C). Such recrystallization results in a relatively fine-grained material but also suppresses warm-temperature superplasticity; deformation at 573 K (300 °C) takes place by dislocation flow in the recrystallized material. At temperatures above the Mg solvus, both warm rolled and recrystallized materials exhibit superplastic elongations but cavitate extensively as a result of deforming by boundary sliding