Good in-depth article, research on the annealing process of finished ultra-thin copper strips
1. Introduction
The purpose of heat treatment is to use a certain amount of heat to change its internal structure and eliminate the metastable plasticity of the structure and properties caused by cold deformation. The strip undergoes recovery and recrystallization annealing to obtain the required comprehensive properties. Finished product annealing refers to the final annealing of the product, which controls the performance of soft products. For this process, we must first meet the various performance indicators required by users, and at the same time, the performance must be uniform and consistent, with no scratches, no foreign objects pressed into the surface, smoothness, and no oxidation. The thickness of ultra-thin copper strip has reached 0.05mm. Because the strip is too thin and the residual stress exists, it is easy to cause bonding in the bell annealing furnace. The finished product annealing technology has become a major technical bottleneck in the research and development of 0.05mm ultra-thin copper strip. .
2. Cause analysis
Ultra-thin copper strips are prone to bonding during the annealing process of the finished product. The reason for bonding is: interlayer bonding is due to the mutual diffusion of copper atoms on the surfaces of two adjacent layers of copper strips at high temperatures during the annealing process. caused by. The greater the degree of atomic diffusion, the more serious the interlayer bonding. The degree of atomic diffusion is directly related to the following process parameters:
1. The size of the interlayer tension
The greater the interlayer tension, the smaller the distance between two adjacent layers of copper strips and the smaller the contact surface.
The larger the product, the greater the number of mutual diffusion of atoms and the greater the degree of diffusion; when the interlayer tension is small, the opposite is true;
2. Annealing temperature and total annealing time
The higher the annealing temperature, the faster the atomic diffusion, the longer the total annealing time, the greater the number of atomic diffusions, and the degree of diffusion is intensified; when the annealing temperature is lower and the total annealing time is shorter, the situation is opposite;
3. Weight of the coil: The greater the weight of the coil, the greater the interlayer tension, the longer the total annealing time required, and the greater the degree of bonding as described in 1 and 2; when the weight of the coil is small, the opposite is true. .
3. Solution
1. Current status of annealing technology for finished copper strips Air cushion continuous annealing: The minimum thickness of annealed strips is 0.1mm, 0.1mm
The following thin strip annealing equipment cannot meet the requirements; bell furnace annealing: heavy annealing and bonding of large coils; heavy annealing of small coils has the disadvantages of poor stability of the furnace coil, high energy consumption, and high cost.
2. In view of the above reasons, after many tests, the following technical solutions have been determined to reduce the tension: on the premise of ensuring that the edge tower shape is not larger than 1mm, the coiling tension is controlled below 12N/mm2; to reduce the coil weight: on the slitting unit Cut finished rolls of more than 5 tons into small rolls of no more than 500kg. A special annealing sleeve and furnace loading spreader were designed and produced. The inner diameter of the steel drum is 300mm.
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After many discussions and tests, it was determined to use a roller hearth continuous annealing furnace for annealing the finished product. The annealing process is shown in Table 1:
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From the observation of the metallographic structure in Figure 2, it can be seen that when the annealing temperature is 360°C, the grains begin to grow slowly, but the grain growth is insufficient. When the temperature reaches 380°C, the grain size is relatively uniform. In terms of internal organization, the smaller and more stable the grain size is, the better the overall performance will be. Therefore, many domestic and foreign manufacturers rely on controlling the grain size to control performance. When the temperature exceeds
At 400°C, or even reaching 420°C, the grain size begins to be uneven. This is the stage where the grains engulf each other and grow up unevenly after recrystallization, and the microstructure is uneven.
4. Conclusion
Through in-depth research on the characteristics of the roller hearth annealing furnace, major technical problems in the annealing and bonding of finished strips have been solved. After a large number of tests and result analysis, the optimal process parameters were determined to be: annealing temperature 380°C, annealing cycle time 30 minutes, and total annealing time 270 minutes. After the 0.05mm ultra-thin copper strip is annealed in the roller hearth annealing furnace, the comprehensive performance analysis of 3 randomly selected coils of T2 and TU2 is carried out. The analysis results are shown in Table 3:
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As can be seen from Table 3, the final performance indicators of the finished strip meet the design requirements, there is no adhesion between layers, and the resistivity can be ensured to be uniform.
