The extremely high ductility shown by certain alloys when deformed at low strain rates at moderately high temperatures. Zinc-aluminium alloys near their eutectoid composition behave this way around 275 C. Normally ductile metals work harden as they deform and neck down locally which rapidly leads to fracture. Superplastic materials do not neck down and can undergo considerable plastic deformation provided the rate is kept below a critical level, thus resembling thermoplastic materials. Similar forming processes are possible but at lower production rates because of the slow deformation rate needed.
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