Microstructure and mechanical properties evolution of a novel selective laser melted Al-Cu-Ni-Zr-Ti alloy during heat treatment

Abstract

This study presents the microstructure and mechanical properties of an additive manufactured Al-Cu-Ni-Zr-Ti alloy fabricated by selective laser melting (SLM). The microstructure evolution during heat treatment at elevated temperatures and its impact on the mechanical properties were also systematically investigated. Results showed that the as-built Al-Cu-Ni-Zr-Ti alloy exhibited a heterogeneous grain structure, which consisted of ultrafine equiaxed and columnar grains at the bottom and top of molten pool, respectively. The L1₂-Al₃(Zr, Ti) phase tends to form within the grains, while the heat-resistant Al₇Cu₄Ni phase preferentially distributes along grain boundaries during the SLM process. As a result, the SLMed Al-Cu-Ni-Zr-Ti alloy, with these unique heterogeneous structures, displays high strength and good heat resistance. The yield strength and elongation of the as-built alloy were measured as 278 MPa and 7%, respectively. When the alloy is exposed to 300 ^oC and 350 ^oC, the yield strength gradually improved with the time extended from 3 h to 200 h. Particularly, after exposure to 350 ^oC for 200 h, the yield strength reached 310.8 MPa, which is 12% higher than the as-built condition (278.3 MPa). Microstructure observation revealed that the refined Al₇Cu₄Ni phase and grains exhibited good coarsening resistance during exposure at 300 ^oC and 350 ^oC, precipitation of nano-sized L1₂-Al₃(Zr, Ti) and θ' phases provide additional strengthening. Therefore, the SLMed cost-effective Al-Cu-Ni-Zr-Ti alloy demonstrates promising suitability as a heat-resistant aluminum alloy within the 300-350°C range, while its thermal resistance at temperatures up to 400°C remains insufficient.