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As an intermediate product in foil production, the microstructure, surface quality of the billet will directly affect the structure and properties of the final product. The thinner the product is, the more obvious the influence of the structure of the returning material is. Compared with hot-rolled billet, the amount of deformation in roll-casting process is much smaller, and the quality of the rolled billet has a more direct impact on the final product.
Most aluminium foils are made of 99.0% - 99.5% industrial pure aluminium. Usually, the higher the purity, the lower the tensile strength and the greater the elongation. Increasing the content of impurities can increase the tensile strength of the recruits, while the elongation decreases. However, when the purity of aluminium is too low, the brittleness of the material increases, and the calendering performance becomes worse. It is easy to produce pinholes, which is not suitable for rolling thin products.
(2) Impurities in industrial pure aluminium are usually Fe, Si, Cu, Mn, Ti, B, C, etc. Some impurities are inherent, while others are deliberately added.
(3) There are always Fe-Si-Al compounds in the second phase and compound industrial pure aluminium. The second phase existing after casting and homogenization is close to equilibrium. It is difficult to change the type, shape and quantity during cold-bonding, and will be preserved in the final foil products. The type of the second phase, particle size, shape, distribution and quantity will have an important impact on the strength, processability, fatigue resistance, decay resistance and other properties of the material. Especially for double-zero foil, the grain thickness is usually larger than that of the box, the grain size is two-dimensional distribution [56_58], the number of adjacent grains is less, and the grain boundary is plane network distribution. Compared with bulk materials, the second phase is more likely to affect the mechanical properties of the box.
(4) When the original grain size is relatively large, especially twins, the twin structure has strong directionality. It is difficult to break up during cold rolling. The hardening rate of the coarse grain area is high and the deformation is difficult, which makes the structure and properties of the box uneven. The rolling shape is difficult to control, and even the strip breakage may occur. After annealing at 0.5 after cold rite, the coarse grains will still be coarse and uneven. In addition, white strips will be produced on the surface, and the pinhole rate of the product will be increased. Therefore, the average grain size is generally less than 70 ^ 011 . But it does not mean that the smaller the grain size, the better. Although grain refinement can increase the plasticity of the material, it also increases the deformation resistance. The hardening degree of the milk is high and it is difficult to produce thinner box.
(5) Adding grain refiner (Al-Ti-B or Al-Ti-C) to the pot solution and introducing heterojunction nucleation can refine the microstructure of caster, reduce the hot cracking tendency of ingot and improve the homogeneity of the structure, especially for rolled or extruded profiles, which can obviously improve the surface quality and processing performance of the deformed products. Reduce surface defects.