| Summary: | In order to enhance the high-temperature mechanical performance to meet service requirements, the microstructures and tensile properties of heat-treated Al-8.4Cu-2.3Ce-1.0Mn-0.2Zr-xNi (x = 0, 0.5, 1.0, 2.0, 4.0 wt.%) were investigated. The metallographic analysis techniques have been used to examine the microstructural changes with different Ni contents. Results show that after adding 0.5% Ni to the Al-8.4Cu-2.3Ce-1.0Mn-0.2Zr alloy, the spheroidized Al<sub>7</sub>Cu<sub>4</sub>Ni phase is formed. With Ni content further increasing, the Al<sub>8</sub>CeCu<sub>4</sub> and Al<sub>24</sub>MnCu<sub>8</sub>Ce<sub>3</sub> phases disappear, and the nano-sized Al<sub>20</sub>Cu<sub>2</sub>Mn<sub>3</sub> and Al<sub>2</sub>Cu phases decrease gradually. When Ni content reaches 4.0%, the Al<sub>3</sub>CuNi phase appears. It turns out that the addition of 0.5% Ni has significantly improved the tensile properties at 400 °C. The ultimate tensile strength, yield strength, and elongation of Al-8.4Cu-2.3Ce-1.0Mn-0.2Zr-0.5Ni alloy at 400 °C reach 103 MPa, 93 Mpa, and 18.0%, respectively, which makes the alloy possible to be employed at 400 °C. The intermetallic micro-skeleton, composed of thermostable Al<sub>8</sub>CeCu<sub>4</sub>, Al<sub>24</sub>MnCu<sub>8</sub>Ce<sub>3</sub>, Al<sub>16</sub>Cu<sub>4</sub>Mn<sub>2</sub>Ce, and Al<sub>7</sub>Cu<sub>4</sub>Ni phases at the grain boundaries as well as nano-sized Al<sub>20</sub>Cu<sub>2</sub>Mn<sub>3</sub> and Al<sub>2</sub>Cu precipitates in the grains, contributes to the good elevated-temperature tensile strength. The fracture mechanism is changed from quasi-cleavage at ambient temperature to coexistence of quasi-cleavage and dimple at 400 °C.
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