Studies On Microstructures And Mechanical Properties Of Ultra-fine Grains Pure Cu, Pure Al And Cu/Al Laminated Composites Processed By Accumulative Roll-bonding (ARB)

Cu/Al ultra-fined multilayer composite has many outstanding potential properties, it may not only contain the as extendable and thermal-and-electrical-conductivity-friendly as ultra-fined copper; but also it may has good corrosion resistance. Besides, it can reduce the weight and price. As it has above better qualities and proves natural-resources-and-energy friendly. It can be widely applied in electronic gadgets and aerospace. In this paper, accumulative roll bonding (ARB) was utilized to fabricate the Cu/Cu, Al/Al and Cu/Al composites. The influence of thickness ratio of pure aluminum and pure copper sheets on the microstructure and mechanical properties of Cu/Al composites was investigated to determine the optimum thickness ratio. The effect of annealing temperature and annealing time on microstructure, interface and hardness of pure copper and aluminum composites was studied. Optical microscope, SEM, EDS, EBSD and TEM were employed to observe microstructure evolution and the interface structure of composites after ARB-process an heat treatment. The micro-hardness test and uni-axial tensile test at room temperature were performed on the composites to evaluate their mechanical properties. The mechanism of microstructural evolution, interfacial bonding mechanism, strengthening mechanism and fracture mechanism of composites were discussed. The results are show as follows:Cu/Al ultra-fined grain laminated composites was processed by accumulative roll bonding (ARB) using different thickness ratio of pure copper and pure aluminum sheets at room temperature. The evolution of interface bonding process, microstructure and mechanical properties were quite similar. And the Cu/Al laminated composite produced with 2 mm thick pure copper and 1 mm thick aluminum exhibits the best boning quality and mechanical properties.The ARB technique not only realizes the metallurgical combination between different laminated materials, but also makes the grain refined to submicrometer or nanometer. The interface was combination preliminarily, and the microstructure was refined due to the large strain imposed on the sheets after the first ARB cycle. During the following ARB cycles, the quality of interfaces bond was gradually improved, and the homogeneity of microstructure was improved while the average grain size didn’t change obviously. When the accumulative strain reaches 4.8, most of the interfaces has achieved its metallurgical combination. The average grain size of pure copper in thickness was from ～50 um to ～0.2 um, while it was refined to about 0.5 um in aluminum layer. The mechanism of grain refinement is mainly due to the dislocation gliding and segmentation and is also with the effect of twinning. After ARB processes, it obtained the typical rolling texture in the middle of the laminated copper sheets, whose main texture component is{110}<112>.The evolution of mechanical properties in different materials is also similar after dififferent ARB cycles. The improvement of hardness and strength mainly occurs in the early ARB cycle. For example, after the first ARB cycle, the yield strength of pure copper increased about 262MPa, which is about 3 times of the annealed sample, while it was about 70MPa and 2 times of the annealed sample in pure aluminum. With the increase of ARB cycles, it was only a slight increase until saturated in the hardness and strength. On the contrary, the elongation to failure decreased sharply in the first ARB cycle, and then kept almost constant or decreased a little during the following ARB cycles. For example, the elongation to failure of pure copper and pure aluminum is about 5% and 10%, respectively. As a result, it exhibits the comprehensive mechanical properties after 6 ARB cycles either in the pure copper or pure aluminum sheets. The strengthening mechanism of multilayered composites processed by ARB is mainly due to the work-hardening and fine-grain strengthening. Besides, the interfaces, non-lubrication friction and work-hardening film during surface treatment and recycling rolling are also the reasons to increase the strength. The laminated composites processed by ARB exhibit the shear ductile fracture characteristics.The grains of laminated composites produced by ARB recrystallized and grew from the interface to the substrate after heat treatment. It showed that the laminated grains processed by ARB had good thermal stability, and the appropriate annealing parameters of pure copper and pure aluminum with different ARB cycles were obtained primarily. It was 350℃/30min, 300℃/30min and 300℃/20min for pure copper after 1,3,6 cycles, respectively, while it was 300℃/30min,250℃/30min and 250℃/20min for pure aluminum after 1,3,6 cycles, respectively.