CNT-reinforced Al-xZr (x = 0.25, 0.5 and 1 wt.%) surface composites fabricated by friction stir processing: microstructural, mechanical and wear characterisation

Abstract

ABSTRACT In the present study, carbon nanotubes (CNTs) were dispersed in the cast Al-xZr (x = 0.25, 0.5 and 1 wt.%) alloys by multi-pass friction stir processing (FSP) to fabricate novel Al-xZr/CNT surface composites. The effect of Al3Zr precipitate and CNTs either separately or in aggregate form on the microstructure, mechanical properties and wear behaviour were investigated. Due to the formation of Al3Zr particles, the addition of Zr modified the microstructure and improved the mechanical and wear properties. As the Zr content increased from 0.25 to 1 wt.%, the grain size reduced from ∼220 µm to ∼106 µm, the tensile strength increased from ∼83 MPa to ∼98 MPa, and the friction coefficient decreased from 0.768 to 0.64. FSP refined the grain structure and caused fragmentation and redistribution of the Al3Zr, improving mechanical and wear properties. The FSPed Al-%1Zr alloy exhibited a grain size of 7.8 µm, tensile strength of 164 MPa and friction coefficient of 0.482. Further improvement in the mechanical and wear properties were obtained by incorporating the CNTs into Al-xZr alloy. In particular, the Al-1%Zr/CNT composite with the grain size of ∼3 µm showed the most significant tensile strength of 215 MPa, the lowest friction coefficient of 0.209 and the highest wear resistance. The improvement in mechanical properties of the composites was mainly attributed to the grain refinement and the load transfer model.