Study On Deformation Behavior Of Copper Sheet And Its Grain Refinement During Step By Step Extrusion-rolling Process

As is well known, many propertiese of metal materials is closely related to its grain size. According to Hall-Petch’s formula, the smaller the grain size, the higher the strength and the hardness. While conventional methods such as deformation rolling, drawing and others can refine grains, but it is difficult to refine to submicron grade. Though many kinds of plastic deformation methods can obtain the materials of submicron grain size, its complicated process and scale production difficulties making it difficult to preparation larger sizes of materials and mass production.To solve these problems, in this paper, an independent designed step by step extrusion-rolling deformation equipment was adopted, deformation behavior and grain size variation of pure copper plate was studied, the feasibility of grain refinement and fine grain materials of mass production was also explored. T2 copper plates was choosen as raw material. Its thickness is 2.020 mm and its purity is 99.90%. By the finite element simulation, the stepping length, advance speed, where should be lubricated and so on were explored. The results of the finite element simulation can be seen as the predictive guidance. The final step length is 20mm, the advancing speed is 10mm/s.In this paper, a series of 1,2,4,6 and 8 passes step by step extrusion-rolling deformation experiment were employed. The die channel interior angle φ≈94° and the outer corner Ψ≈5°. After that, the samples were heat treated and the process was researched. In order to reduce the workload yet to fully examine the influence of various factors, Orthogonal experiment design scheme were utilized:Four levels of extrusion deformation pass are respectively one-pass, two-passes, four-passes, eight-passes; Four levels of the heat treatment temperature are respectively 200℃,230℃,260℃,300℃; Four levels of holding time are respectively 10min,15min,20min,30min. After heat treatment, the specimens of each group were quenched by using water.After 4 passes deformation,the average grain size of the specimens’ cross section by homogenization annealing state of 28.32μm is refined to 4.49μm, the grain size is reduced by about 84.1%. Through the analysis of orthogonal test, the best heat treatment for the materials is found:eight-passes, annealing temperature is 230 ℃, holding time is 10min. The average grain size of the obtained samples is about 3.79μm. Hardness of the fourteenth orthogonal experiment samples is 1.81 times that of the initial annealing state. The results suggest that: With the deformation passes increasing, the grain size decreases; Reasonable heat treatment process can effectively ameliorate the microstructure of pure copper.It can be seen that, in this paper, the refinement of grain size is no longer obvious after 8 passes step by step extrusion-rolling deformation. The grain size steady in range of 3-6 μm. This study have great reference value for the continuous production of large size ultrafine grained materials.