چكيده به لاتين
In this research, the microstructure and mechanical properties of the copper-steel layered composite produced by the cumulative rolling joining process were investigated during four cycles. The working method has been such that before each cycle of the cumulative rolling joining process, in order to connect the proper bond between the layers, the samples were placed at a temperature of 873 degrees Kelvin for 5 minutes. The microstructural results showed that due to the formation of an oxide layer caused by the preheating operation, the lack of bonding at the interface of the layers was created during different cycles. Also, with the increase in the number of cycles, a severe throat phenomenon appeared in the steel reinforcement layer. In terms of grain size, it can be stated that during the first to fourth cycles of the cumulative rolling joining process, the grains of the microstructure of the steel base became elongated. However, in the copper layer, in the first cycle, due to the stress caused by the rolling process, the copper grains became elongated, and during the second cycle, due to the cumulative rolling joining process and subsequent heat treatment, the phenomenon of recrystallization and grain growth occurred. Finally, during the fourth cycle, a combination of ultra-fine grains resulting from recrystallization and crushed grains resulting from the cumulative rolling joining process was created in the microstructure of the copper background. In terms of mechanical properties, it can also be stated that due to hard work during the initial cycles and due to ultra-fineness during the final cycles, hardness and strength have continuously increased and the amount of increase in length and toughness of the layered composite has continuously decreased. Of course, the phenomenon of recrystallization and grain growth has occurred in the copper layer from the second cycle onwards; However, the effect of hardness and crushing of grains was overcome by the effect of recrystallization and grain growth, so that the strength and elongation increased from 440 MPa and 7.4%, respectively, during the first cycle to 480 MPa and 1.8%, respectively, during the fourth cycle. In terms of the fracture surface, it can also be stated that the fracture surface of the steel layer, during the first cycle, was in the form of complete soft fracture; But as a result of the hard work created during the fourth cycle of the cumulative rolling joining process, the fracture surface of the steel layer has become brittle. In the copper layer, during the first cycle, due to the presence of deep and coaxial dimples, the fracture surface of the copper layer is a complete soft fracture, and during the fourth cycle, due to the shear stress caused by the cumulative rolling joining process, the shape of the dimples is shallow and elongated, which is a characteristic of soft shear fracture.
