Microstructure and mechanical properties of squeeze-cast Al-5.0Cu-1Mn-based alloys with different Ni content.

[Display omitted] • The mold-filling capacity and mechanical properties of Al-Cu-Mn alloy were improved by adding appropriate Ni element. • After T6 treatment, the Ni-rich eutectic phase spheroidized into discrete particles and distributed along grain boundaries. • Proper addition of Ni will lead to Ni atoms segregated into the interface between the Mn-rich phase and α-Al matrix, which reduces the interfacial energy of Mn-rich phase and prevents it from growing. • The Al-5Cu-1Mn-1Ni alloy have the optimum mechanical properties with ultimate tensile strength, yield strength and elongation at fracture reaching 505MPa, 348MPa and 16.5%, respectively. In this study, the effects of Ni content on the microstructure and mechanical properties of Al-5.0Cu-1Mn-based alloys were investigated. The results demonstrate that Ni alloying refines the grain size and enhances castability. At low Ni content, some of Ni atoms participate in forming Al 7 Cu 4 Ni at the grain boundaries. The rest Ni segregates to the interface between α-Al and AlCu 3 Mn 2 phase, which inhibits AlCu 3 Mn 2 growth. The amount of Ni-rich phase at grain boundaries increases significantly as Ni concentration increases at the expense of the decline precipitates. After T6 treatment, the lamellar Ni-rich phase spheroidized into discrete particles that were uniformly distributed along the grain boundaries. Ni-rich phase of particles can effectively pin grain boundaries and prevent grain rotation. The optimum mechanical property is achieved with 1% Ni addition, predominantly due to the synergistic strengthening of eutectic strengthening and precipitation strengthening. The ultimate tensile strength, yield strength and elongation reach 505 MPa, 348 MPa and 16.5% respectively, which far exceed the current commercial cast aluminium alloys. With increasing Ni concentration, the fracture mode of the alloy changes from ductile fracture to brittle-ductile mixed fracture, because the high amount of Ni-rich phase intermetallic compounds increase the sites for localized brittle fractures. [ABSTRACT FROM AUTHOR]