Investigation Of Hot Processing With Temperature-rise By Rolling Deformation In Pure Copper During Three-roll Planetary Rolling

Three-roll planetary mill processing is a mature manufacture technique,which is typically characterized by one-pass rolling with large deformation reduction,severe temperature-rise and sharp microstructural evolution.With the enlargement of the application fields and the urgent improvement of the quality requirements of copper tubes,it is of great significance to perform research on hot processing with temperature-rise by rolling deformation during three-roll planetary rolling(in abbr.PSW).In general,dynamic recrystallization plays an important role in refining the grain of metals,making the microstructure uniform and obtaining good mechanical properties during plastic deformation.Models to predict whether dynamic recrystallization occurs at least need to verify the following parameters,strain and temperature,in which finite element models can not provide all of the constants together,and even certain models relevant lacks convincing experimental and data support.So it is necessary to establish an analytical model to give both the strain field,temperature field and stress field during PSW.Simultaneously combined with the evolution of the microstructure,the models list above can be contributed to discuss the physical essence of metals processing,which lay the foundation for the large-scale industrialization of PSW.Microstructures of pure copper were analysized by optical microscopy(OM)and electron backscattered diffraction(EBSD).Results show that after three roll planetary processing,grains in pure copper were refined along axial direction,while grain inhomogeneity was diminished accordingly.In radius-reducing zone microstructures of pure copper show gradient distribution tendency till finally it turns into homogeneously distributed and in centralized processing zone gradient microstructure vanished at the outer region of copper tube.Grain size of the final tube is about 2.1 ± 1.2?m.And the texture of pure copper is proved to be similar to certain rolling texture which is weakened by recrystallization as a result of temperature-rise during rolling.In this dissertation,geometric models of pure copper processed by PSW were firstly built with optimum velocity field and the boundary conditions.Secondly strain field of the sample was introduced,shear strain being combined into equivalent strain rationally.To ensure the accuracy of the simulation results,the constitutive equation of pure copper was carefully chosen to build appropriate relationship among stress,strain and temperature.At the same time,power law is used to parse the Instantaneous differential equation during working.Although the detailed differential equation may not be solved completely in mathematics,numerical simulation of processing can be replaced to calculate the temperature field and stress field of steady-state processing.There are two ways for managing physical essence of pure copper during PSW:calculation and prediction by theoretical models,verification by numerous experimental data.Calculation results of theoretical models were in line with the evolution of microstructures and distribution of Vickers hardness.In the meantime,dynamic recrystallization behavior of pure copper during processing was predicted and verified by calculation.To sum up,concerning recrystallization in result of temperature-rise,theoretical analysis of the steady-state process of pure copper during PSW was carried out in this paper,which lays the foundation for the application of recrystallization model during PSW in actual production.It also provides a theoretical basis for the promotion and application of the PSW.