Effect of ingot grain refinement on the tensile properties of 2024 Al alloy sheets

Microstructures of the coarse grain (CG) and fine grain (FG) 2024 Al alloy ingots prepared by different casting procedures are investigated, and the microstructures and tensile properties of the two naturally aged CG and FG 2024 Al alloy sheets prepared from the two ingots are compared. Metallographic observation reveals similar recrystallized grain structures of the two solution treated 2024 Al alloy sheets, but EBSD analysis demonstrates that a non-complete recrystallized substructure is formed in the CG sheet, whereas the FG sheet recrystallizes completely after solution treatment. SEM observation indicates that the remaining phases in the FG sheet are less, smaller and are more dispersedly distributed than that in the CG sheet. These microstructural differences between the two sheets result in slightly lower strengths and higher ductilities in the directions parallel to the rolling plane, and markedly higher strength and ductility in the ND direction for the naturally aged FG sheet. These findings suggest the possibility of improving the mechanical properties, including toughness and fatigue properties, of Al profiles by refining their ingot grain structures.