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

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.