Effects of Ni on the microstructure, mechanical and tribological properties of AA2024-Al3NiCu composite fabricated by stir casting process

Highlights: • The AA2024-Al₃NiCu composite was fabricated by the stir casting process and homogenization heat treatment. • By increasing nickel from 3 to 4.5 wt%, the T-Al₆Mg₄Cu precipitates formed instead of S-Al₂CuMg precipitates. • The nickel aluminide reinforcement decreased the coefficient of friction and wear rate of the composite. -- Abstract: This research has studied the microstructure and mechanical and tribological properties of AA2024 aluminum alloy matrix composite reinforced by Al₃NiCu. The Al₃NiCu intermetallic was created in the aluminum matrix by adding nickel during the stir casting process and then performing the homogenization treatment. According to the results, the block-shaped Al₇Cu₂Fe and Al (Cu, Mn, Fe, Si) compounds formed an integrated structure at the interdendritic regions. Moreover, with the addition of nickel up to 1.5 wt%, the fine needle-shaped Al-Cu-Mg precipitates near the interdendritic regions increased, but further addition of nickel reduced their amount at this zone. After homogenization treatment, with the addition of nickel up to 4.5 wt%, the needle-shaped Al-Cu-Mg precipitates in the interdendritic regions disappeared and precipitated at the inner zone of dendrites. By adding nickel and performing homogenization treatment, unreacted Ni and Al₃Ni intermetallics were completely transformed to Al₃NiCu. Furthermore, with the rise in nickel from 3 to 4.5 wt%, the T-Al₆Mg₄Cu precipitates formed instead of S-Al₂CuMg precipitates in the aluminum matrix. The addition of 3 wt% nickel lowered the coefficient of friction and wear rate of the composite by about 13% and 12%, respectively, while raising the strength by almost 42%, compared to those of the sample without nickel.