Effects of Heat Treatment on the Interface Microstructure and Mechanical Properties of Friction-Stir-Processed AlCoCrFeNi/A356 Composites

Equiatomic AlCoCrFeNi high-entropy alloy (HEA) has gained significant interest in recent years because of its excellent mechanical properties. A356 aluminum alloy reinforced by AlCoCrFeNi HEA particles was fabricated by friction stir processing (FSP) and subsequent heat treatment. Solution and aging treatments were specially performed for the composites to control the interface microstructure, and interfacial microstructure and tensile properties were explored at different conditions. The interface between the matrix and HEA particles showed a dual-layered core-shell structure and the thickness of the shell region increased with the solution time. The microstructure located in the shell layers consisted of a solid solution with increasing aluminum content, in which a radial-shaped solid solution phase formed in the region close to the core of the HEA particle and scattered solid solution grains with high Ni content formed in the region close to the matrix alloy. The gradient of composition and microstructure across the HEA/Al interface can be obtained through heat treatment, and an optimal interface bonding state and mechanical property were obtained after solution treatment for 2 h. Compared with FSPed A356 aluminum alloy, the FSPed composite enhanced the tensile stress by 60 MPa and the stain by 5% under the optimized conditions. The overgrowth of the shell layer decreased both the tensile strength and the ductile greatly due to the formation of a radial-shaped solid solution phase in the shell region.

Automated summary

A356 aluminum alloy reinforced by AlCoCrFeNi high-entropy alloy (HEA) particles was fabricated using friction stir processing (FSP) and subsequent heat treatment. Solution and aging treatments were performed to control the interface microstructure and explored its effect on tensile properties. The interface showed a dual-layered core-shell structure, with the shell thickness increasing with solution time. The microstructure in the shell layers consisted of a solid solution with increasing aluminum content, forming radial-shaped solid solution phase close to the core and scattered solid solution grains with high Ni content close to the matrix alloy. The FSPed composite exhibited enhanced tensile stress and strain compared to the FSPed A356 alloy. The overgrowth of the shell layer decreased tensile strength and ductility due to the formation of a radial-shaped solid solution phase.