Abstract
Electron backscatter diffraction (EBSD) technique was used to analyze the microstructure of cold-rolled C71500 cupronickel alloy tube. Through the analysis of microhardness, tensile properties, microstructure, texture, and texture content of the cupronickel alloy tube after the second pass cold rolling with different deformations (3.19%, 9.57%, 19.37%, 23.97%, 31.78%), the texture change law of the alloy was obtained. The quantitative relationship between deformation and storage energy was revealed by analyzing the grain size and the change of texture and grain boundary, which could be directly reflected by the proportion of small angle grain boundaries. The optimal deformation of second pass rolling for C71500 alloy was obtained. Results show that the yield strength, tensile strength, and microhardness of cupronickel alloy are increased with increasing the working ratio, while the plasticity is decreased.
Science Press
Many methods have been proposed to study the texture of copper and cupronickel alloys, for example, the micro-structure and properties of Cu alloy tube were analyzed by three-roll planetary rolling proces
This research mainly studied the effect of multi-pass rolling process on the properties of C71500 cupronickel alloy tube. After the first large deformation rolling and annealing, the influence of multi-pass deformation with different working ratios on the texture and grain boundary of C71500 alloy of uniform structure was studied, and the corresponding mechanism was also revealed. The results provided a theoretical basis for the optimal selection of deformation, the thermodynamics of forming special grain boundary, and the subsequent deformation processing design of C71500 alloy tubes.
The experiment material C71500 alloy consisted of 30.54wt% Ni, 0.93wt% Mn, 0.80wt% Fe, and balance Cu. The alloy was smelted by vacuum induction melting furnace. Then the obtained ingot was hot-rolled and perforated to prepare tube blank. After the rolling deformation of 70% by two-roll periodic cold rolling mill, the alloy tube was annealed at 800 °C for 20 min, and then cooled down and used in protective atmosphere. The annealed tubes were rolled with different deformations by the three-roll periodic cold rolling mill to study the influence of deformation on the texture of tubes. The specific rolling procedure is shown in
The electron backscatter diffraction (EBSD) observation was conducted on the longitudinal section along the rolling direction (RD) of tube. The electrolyte consisted of 25vol% H3PO4, 25vol% C2H5OH, and 50vol% H2O, the polishing voltage was 20 V in direct current (DC), and the polishing time was about 180 s. Scanning electron microscope (SEM) of Gemini SEM300 of Zeiss brand was used to observe the microstructures, and orientation analysis was conducted by Channel 5 data processing software. The microhardness of alloy was measured by Buehler Wilson VH1150 Vickers microhardness tester with the load of indenter of 5 kg for 10 s. The tensile test of alloy was conducted by SUNS UTM5205 electronic universal tester.
Fig.1 Inverse pole figures (IPFs) of C71500 alloy tubes after different deformations: (a) 0.00%, (b) 3.19%, (c) 9.57%, (d) 19.37%, (e) 23.97%, and (f) 31.78% (TD: transverse direction)
A small deformation can produce a certain number of non-coherent twin boundaries. According to Chen et a
Orientation distribution function (ODF) was used to quantitatively analyze the texture of the alloy, as shown in Fig.2. The maximum and the minimum density value of tex-ture is 4.02 and 0.14, respectively. The texture is mainly the typical annealed texture of face centered cubic, such as R-Cube{001}<110>, R-Brass{111}<110>, and RZ{111}<112> textures. As shown in Fig.2b, after deformation of 3.19%, the texture orientation strength is increased, the maximum and the minimum density of texture is increased to 4.32 and 0.13, respectively, and the R-Cube{001}<110> texture becomes stronger. At the same time, the strength of Brass{110}<112> texture and R-Brass{111}<110> texture obviously decreases, resulting in the weakening of annealing texture orientation. When the deformation reaches 9.57%, the R-Cube{001}<110> texture turns to the Cube{100}<100> texture, the R-Brass{111}<110> texture becomes stronger, and the RZ{111}<110> texture can be observed. When the deformation reaches 19.37%, the texture of Cube{100}<100>, R-Cube{001}<110>, and normal direction (ND)-Cube{001}<310> can all be observed, indicating that the grain direction turns to {100} crystal surface, and there are a small number of R-Brass{111}<110> and RZ{111}<110> textures. When the deformation continuously increases to 23.97%, the grains mainly consist of R-Cube{001}<110> texture and a small number of R-Brass{111}<110> and RZ{111}<112> textures. When the deformation reaches 31.78%, R-Cube{001}<110> and RZ{111}<110> textures are strengthened, whereas the R-Brass{111}<110> texture disappears and is gradually transformed into Rolled{112}<110> texture. With increasing the deformation, the orientation of texture becomes more obvious, and the maximum density of texture is increased from 3.48 to 6.32.
The rolled tube, plate, and wire of copper alloys are different. The results of appearance of RZ{111}<112> texture during the deformation process are similar to those of TP2 alloy tube during rolling proces
Fig.3 shows the changing rule of mechanical properties of C71500 alloy tubes with different deformations. It can be seen from Fig.3a that with increasing the working ratio, the yield strength (Rp0.2), tensile strength (Rm), and microhardness (HV5) all show an upward trend, while the plasticity (elongation, A) of the C71500 alloy tubes shows a downward trend. Microhardness (HV5) can reflect the change rule of Rp0.2. When the rolling deformation is 3.19%, the yield strength of cupronickel alloy increases by 64.71 MPa, while the tensile strength increases by 1.49 MPa, compared with the properties of the original alloy. When the deformation reaches 31.78%, the yield strength of cupronickel alloy increases by 104.77 MPa, while the tensile strength only increases by 65.29 MPa, and the elongation decreases from 31.02% to 13.64%, compared with the properties of the original alloy. The change trend of microhardness is consistent with that of the yield strength, thereby reflecting changing rule of yield strength. During the deformation process, the C71500 alloy is gradually hardened, the grain is refined gradually, and the grains change to the ones along the direction of <111>, forming the sub-crystalline structure which hinders the movement of dislocation, improves the strength, and reduces the plasticity of the alloy.
1) The optimal rolling deformation for C71500 alloy tube is 9.57%.
2) The texture of C71500 alloy tube is mainly dominated by the transformation among R-Cube{001}<110>, R-Brass{111}<110>, RZ{111}<112>, and Rolled{112}<110> textures.
3) The yield strength, tensile strength, and microhardness of C71500 alloy are increased with increasing the working ratio, while the plasticity of the alloy is decreased. The change rule of microhardness of the alloy can well reflect that of the yield strength of the alloy.
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