There are provided an apparatus and an associated method for manufacturing superplastically formed structural assemblies from preforms. The apparatus includes first and second co-operable dies structured to define a die cavity therebetween for at least partially receiving the preform, at least one heater in thermal communication with the die cavity for heating the preform to a forming temperature, and at least one injector in fluid communication with the die cavity. The injector is structured for injecting pressurized gas into the die cavity to urge the preform against one of the dies to form the preform into the structural assembly. Further, at least one of the injectors is structured for injecting a quenchant into the die cavity to thereby heat treat the structural assembly while distortion of the structural assembly is being at least partially restrained by at least one of the dies.