Investigation of the Stress-Strain State and Microstructure Transformation of Electrotechnical Copper Buses in the Deformation Zone during Continuous Extrusion

A comprehensive study of the features of physical and mechanical processes occurring in the deformation zone of metal during continuous extrusion is carried out with rectangular Cu-ETP buses 10 x 60 mm in size. With the use of finite element computer simulation, values of the power parameters of the extrusion process are obtained. It is noted that the values of the torque and force increase until the free space of the press chamber is filled with metal, reaching maxima of 12.26 kN m and 1.54 MN, respectively. As a result of an analysis of the stress-strain state of metal in the deformation zone, the fields of distribution of equivalent strain, strain rate intensity, and average stresses are obtained and the graph of change in the metal temperature with the time of the extrusion process is plotted. The maximum of the equivalent strain and compressive stresses are observed in the region of contact between the workpiece and the abutment of the press container. That is also where the most intense deformation-induced heating of the metal occurs. A comparison of the results of modeling and microstructural studies indicates that a significant part of work on refining the cast structure takes place at the entrance to the deformation zone and in the abutment region, where the level of compressive stresses is the highest. Plastic deformation of the metal passing through the die leads to the formation of an oriented crystal structure with a grain size of 25 to 30 mu m. The results of measuring the hardness of the samples are very consistent with the results of analyzing the structure in the studied regions of the deformation zone. When the workpiece passes through the abutment region of the press container, deformation-induced heating occurs, which leads to a decrease in the hardness from 93 to 67 HV. After the metal passes through the die, recrystallization processes continue in it, leading to a slight increase in grain size and, accordingly, a decrease in the hardness from 79 to 74 HV, which lasts until the bus comes into contact with a cooling medium.