A high-temperature die casting die includes a first die plate with a first recess and a second die plate with a second recess, the first and second recesses defining a main part cavity and gating. A grain selector is in fluid communication with the main cavity, and an in situ zone refining apparatus is adapted to apply a localized thermal gradient to at least one of the first and second die plates. The localized thermal gradient and the at least one die plate are movable relative to each other so as to apply the localized thermal gradient along a first direction extending from the grain selector longitudinally across the main part cavity.