Evolution of microstructure and mechanical properties of graphene oxide-reinforced aluminum alloy (6061) composite fabricated via accumulative roll bonding

Abstract

This study investigates the fabrication and characterization of Al alloy matrix composites reinforced with graphene oxide (GO) using accumulative roll bonding (ARB). The annealed Al 6061 sheets were processed through 5-pass ARB with GO reinforcement applied during the initial passes. Scanning electron microscopy revealed effective mitigation of GO agglomeration and improved interface bonding due to microscale material mixing. Raman spectroscopy confirmed the strong interaction between GO and the Al alloy matrix, as evidenced by the increased D band intensities and enhanced 2D band symmetry. Mechanical testing indicated an approximately 338.37% increase in yield strength (YS) and 86.42% improvement in hardness for the ARB-processed (ARBed) Al 6061/GO composite (0.2wt%) compared with annealed Al 6061 and an approximately 14.15% increase in YS and 17.23% improvement in hardness for the ARBed Al/GO composite (0.2wt%) compared with unreinforced ARBed Al 6061 specimens after five passes. X-ray diffraction analysis indicated an increased dislocation density, corroborating the observed enhancements in mechanical properties. Fracture surface analysis revealed reduced elongation with deep dimples, highlighting the tradeoff between strength and ductility. These results demonstrate the effectiveness of ARB for integrating GO into the Al 6061 matrix to improve the mechanical performance and interfacial bonding and underscore its potential for advanced composite materials.

1. Introduction

The broad spectrum of industrial applications of Al matrix composites is attributed to their exceptional specific properties, including light weight, elastic modulus, thermal conductivity, electrical conductivity, strength, low coefficient of thermal expansion, and wear and corrosion resistance [1–2]. Pure Al and Al alloys are among the most commonly used materials in multilayered composites because of their excellent properties, affordability, and widespread availability. In many applications, metals and their alloys cannot simultaneously satisfy strength and stiffness requirements. Therefore, metal–matrix composites (MMCs) must be prepared. MMCs made from light-metal alloys are known for their lightweight nature and exceptional mechanical properties, making them ideal for applications in the automotive, defense, and aerospace sectors [3–5]. MMCs derive their flexibility from the metal matrix and their rigidity from reinforcements that are commonly composed of particles, monofilaments, or ceramic fibers. Conventional methods for producing MMCs, such as casting and powder metallurgy, often have limitations, including high manufacturing costs and defects such as porosity and reinforcement clustering. These shortcomings reduce uniformity, impacting the mechanical and electrical performance of the composite [6–7].

To overcome such challenges, this study investigates an alternative approach known as accumulative roll bonding (ARB) [8]. In addition to producing the composite, ARB significantly reduces the size of the matrix grains, making it suitable for ultrafine-grain (UFG) materials [9]. Severe plastic deformation (SPD) techniques such as high-pressure torsion, equal-channel angular processing [10], and ARB [11–12] are utilized to manufacture MMCs. ARB is one of the most versatile techniques owing to its straightforward process. This involves repeated stacking, cutting, and rolling, which significantly increases the dislocation density [13]. Generally, cold-roll bonding is used to create composites strengthened with particles, whereas hot-roll bonding is more suitable for fabricating laminates of different metals and their alloys [14]. Hot ARB offers higher bonding strength because the materials are processed more easily at higher temperatures compared with cold ARB [15]. Furthermore, ARB’s lower processing temperature compared with casting helps avoid destructive interfacial reactions, porosity, and inclusions. The primary objective of ARB is to achieve a metal with UFGs and exceptional mechanical properties [16]. Fabrication of MMCs using ARB involves two distinct approaches. In one method, particles are used as reinforcement and added between metal layers at the beginning of the ARB cycles [17]. A uniform particle dispersion can be achieved after reaching a critical total strain or reduction [18–19]. Another approach combines ARB with a coating method [7,20]. In this technique, a coated strip is inserted between uncoated metal strips. As ARB progresses, the coated layer breaks and evenly disperses within the metal matrix owing to the different flow properties of the coated layer and matrix. Over the past decade, graphene has attracted considerable attention for the advancement of multifunctional MMCs owing to its unique combination of ther