Novel high-strength Al-Cu-Cd alloy fabricated by arc-directed energy deposition: Precipitation behavior of the Cd phase and grain evolution

In this study, a simple and efficient method for obtaining high strength and ductility, i.e., microalloying with Cd, was used for the Al-Cu alloy fabricated by the arc-directed energy deposition (Arc-DED). The resulting deposits exhibited fully equiaxed grain characteristics, and the higher growth restriction factor caused by the higher content of Ti and large nucleation density of Al₃Ti precipitates led to the formation of fully α-Al equiaxed grains during solidification, unlike other Arc-DED-deposited Al alloys. A relationship between the number of Al₃Ti nuclei and the cooling rate during the Arc-DED process was established. Furthermore, the orientation relationship between the Cd phase and α-Al matrix was defined. The Arc-DED-fabricated material was T6 heat-treated (solution + artificial aging). In the aging stage, the metastable nanoscale Cd particles precipitated with a spherical shape (2 nm in diameter) into a face-centered cubic structure with lattice parameters similar to the α-Al matrix, as suggested by the in-depth transmission electron microscopic analysis. The T6-treated Arc-DED-deposited Al-Cu-Cd alloy shows a superior balance of strength and ductility (yield strength of 414.0 MPa, ultimate tensile strength of 475.8 MPa, and elongation to failure of 11.9%) and outperforms other additively manufactured Al-Cu-based materials. This superior tensile mechanical performance is attributed to its finely distributed and equiaxed grains, and the high density of the strengthening θ′-Al₂Cu phase.