6061 Al/Cu layered composites with high strength and well interfacial bonding prepared by accumulative roll bonding

Abstract

6061 Al/Cu layered composites were fabricated by accumulative roll bonding (ARB). The microstructural evolution was examined using scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. After seven ARB cycles, the tensile strength increased to 416 MPa, whereas the elongation decreased to 6.7%. The strength enhancement is mainly attributed to work hardening and grain refinement. No brittle intermetallic compounds (IMCs) were detected at the interface, and interfacial bonding improved with additional ARB cycles. The small hardness difference between Al and Cu promoted uniform plastic deformation across layers, enhancing interfacial cohesion. However, strain localization due to different work hardening responses of Al and Cu led to pronounced shear band formation after seven ARB cycles, reducing the plasticity.

1. Introduction

Al/Cu composites have received extensive research interest in recent decades due to their remarkable mechanical and physical properties, electrical conductivity, cost efficiency, and scalability for mass production [1,2]. Traditional fabrication methods for Al/Cu composites include friction stir welding, laser cladding, and explosive welding [3−6]. However, conventional rolling processes are restricted by low reduction ratios. The accumulative roll bonding (ARB) technology, developed by SAITO et al [7], addresses this limitation, enabling the formation of ultrafine-grained sheets. ARB process is widely utilized for fabricating dissimilar metal composites due to its straightforward equipment requirements and low processing costs [8−11]. Recent studies have concentrated on employing ARB to produce Al/Cu composites [12]. For instance, EIZADJOU et al [13] successfully fabricated Al/Cu composite sheets via ARB. Compared to other solid-state welding techniques, such as friction stir welding and explosive welding, ARB operates at lower bonding temperatures while producing high-strength, ultrafine-grained composites with cleaner interfaces and superior mechanical properties.

Interfacial adhesion significantly influences the performance of layered composites. ZHAN et al [14] indicate that the interface formed during the final processing cycles exerts the most substantial effect on composite performance. Although earlier-pass interfaces can be improved through subsequent ARB cycles, thermal processing presents challenges [15,16]. Specifically, heat treatment can lead to the formation of intermetallic compounds (IMCs) at the interface, which adversely affects interfacial adhesion strength. WANG et al [17] found that IMC formation during hot rolling results in a continuous reduction in interfacial strength as the thickness of the IMC layer increases. This degradation is linked to crack initiation caused by the recrystallization of brittle IMCs at the composite interface [18]. While XU et al [19] successfully combined ARB with intermediate annealing to improve metallurgical bonding and layer continuity, this method introduces trade-offs. Annealing can result in embrittlement due to IMC formation, leading to a decrease in tensile strength and elongation [20]. Furthermore, excessively high annealing temperatures can worsen necking instability at the layer interfaces [21]. Addressing the combined effects of IMC embrittlement and localized necking is essential for optimizing the mechanical performance of composites.

The mechanical properties of the layered composites are significantly compromised by the presence of shear bands (SBs) [22−25]. During the ARB process, the hard layer of the bimetallic composite displays greater resistance to deformation.