Multilayer T₁ phase precipitated on grain boundary in artificially aged Al–Cu–Li alloy

Precipitation-strengthened Al–Cu–Li alloys are commonly used as structural materials in aerospace equipment. The present work focused on investigating the characteristics of grain boundary T₁ precipitate in a rolled Al–Cu–Li alloy. It was found that the T₁ phase with a multilayer structure will precipitate at the grain boundary after artificial aging, and it is nearly continuously distributed along grain boundaries in the pre-rolled samples. The habit plane of the intergranular T₁ normally parallels a (111) plane of the matrix on one side of the grain boundary. And compared to the preferential growth of platelet edges for the intragranular T₁, the grain boundary T₁ phase is also prone to thickening via the stacking of successive unit-cell-thick (0.935 nm) layers on the existing broad surface of the plate, resulting in the significant coarsening in the direction perpendicular to its habit plane. In addition, the reason for the obvious thickening of the grain boundary T₁ phase was also discussed.