The formability investigation of CNT-reinforced aluminum nano-composite sheets manufactured by accumulative roll bonding

Abstract

There is an increasing demand for materials with outstanding mechanical properties for many applications. Ultrafine-grained (UFG) materials as a path for improving the base materials and composite materials as a media for combining the superior properties of different materials are the current solutions for the demanded properties. Severe plastic deformation can be used for manufacturing UFG materials with nano-structure. In this research, accumulative roll bonding (ARB), as a severe plastic method, is utilized for manufacturing aluminum matrix composites reinforced with carbon nano-tubes (CNT). An experimental platform is used to investigate the mechanical properties of ARB-ed AA1200 nano-composites with 2, 6, 32, and 128 layers. Tensile deformation via the Lankford parameter is used to study the anisotropy of the samples. It is observed that this parameter is a function of the number of ARB cycles and increases significantly by increasing the ARB cycles. Moreover, the Hollomon analysis is used to investigate the strain-hardening behavior of the samples. The results showed that the strain-hardening exponent of ARB-ed AA1200 sheets reinforced with CNT decreases by increasing the number of ARB cycles. The formability of the ARB-ed AA1200 nano-composite samples is investigated analytically by the Marciniak–Kuczinsky model and experimentally using the Erichsen tests. The results revealed that the tensile properties are enhanced and more homogenous structures are obtained; however, formability is reduced. In order to obviate this issue, annealing the samples for 30 min at 250 °C was adapted. As a result, formability is improved at the cost of a slight reduction in strength. The obtained results can be due to recrystallization and grain growth alongside the dissolving of the brittle intermetallic oxides at the interface of the layers after annealing. Annealing is used as a mediator to reach a balance between strength, ductility, and formability, so an appropriate formability is achieved at the end.