Reduced final grain size of unrecrystallized wrought material produced via the direct chill (DC) route

A method, comprising:

• forming an embryonic ingot by supplying molten metal to a mold and extracting heat from the molten metal to form an external solid shell, wherein the molten metal is a 7xxx series aluminum alloy;
• solidifying an internal molten core of the embryonic ingot as the embryonic ingot is advanced in a direction of advancement away from the mold and additional molten metal is supplied to the mold, wherein solidifying the internal molten core comprises extracting heat from the internal molten core through the external solid shell;
• and
• continuously forming a high-strength zone within the external solid shell at a cross section of the embryonic ingot that is perpendicular to the direction of advancement and that intersects the internal molten core, wherein the high-strength zone is located between an outer surface of the external solid shell and the internal molten core, and wherein forming the high-strength zone includes reheating the external solid shell at the cross section to induce dispersoid precipitation in the external solid shell,
• wherein reheating the external solid shell at the cross section comprises reheating a portion of the external solid shell to a temperature suitable for precipitating dispersoids, wherein the temperature is lower than a homogenizing temperature of the molten metal and is between 400° C. and 420° C., and wherein the method further comprises maintaining the temperature at the portion of the external solid shell for at least 3 hours.