ã€China Aluminum Industry Network】 With the increasing application of aluminum foil and the increasing demand, the domestic aluminum foil industry continues to develop, especially for the flexible packaging aluminum foil industry. In addition to the use of high quality double-zero aluminum foil in electrolytic capacitors, more than 90% of aluminum foils for packaging are double-zero aluminum foils. The number of pinholes in the aluminum foil is related to the thickness of the aluminum foil. As the thickness of the aluminum foil is reduced, the number of pinholes increases rapidly. When the thickness is more than 0.02mm, the aluminum foil can be completely pinhole-free. The pinhole is one of the main defects of aluminum foil, and it is a defect that has a relatively serious influence in all defects. It is also the existence of a pinhole, so that the oxygen permeability and the water vapor transmission rate of the aluminum foil are not zero. The size and number of aluminum foil pinholes have a decisive influence on the moisture resistance, gas barrier and opacity of aluminium foil and its composites. 1 Influence of aluminum foil blank on pinhole degree The status of aluminum foil blank directly affects the quality of rolled products and the yield of finished products. As the thickness of aluminum foil decreases, various defects hidden in the interior of the billet, such as inclusions, bubbles, foreign matter, and coarse second phase particles, will gradually be exposed, which will adversely affect the rolling of aluminum foil and product quality, such as the formation of Perforations or cracks, severe aluminum foil will break. Statistical data show that the number of pinholes in aluminum foil increases with the increase in the amount of inclusions and the size of the compound, and increases exponentially as the thickness of the aluminum foil decreases. Various defects existing on the surface of the blank, such as scratches, peels, water spots, and dirt, will continue to exist on the surface of the aluminum foil in an elongated form. When the amount of reduction reaches a certain level, the aluminum foil will perforate or fracture. 1.1 The influence of the chemical composition of the aluminum foil blank on the pinhole number of the aluminum foil The compound phase in the aluminum foil mainly includes α (FeSiAl) phase, β (FeSiAl) phase and FeAl3 phase. The α(FeSiAl) phase is an ideal as-cast compound. This phase is dominated by skeletal and round particles, and is easily broken during the deformation process. It is easier to dissolve into the matrix during the homogenization process. The FeAl3 phase is a needle. In the case of a sheet-like compound, this coarse compound phase forms a crack source during the rolling of the aluminum foil and expands to form pinholes. The compounds of the imported billet mainly consist of α(FeSiAl) and β(FeSiAl) phases, while the compounds in the domestic aluminum foil mainly consist of α(FeSiAl) and FeAl3 phases. This also results in the number of pinholes in domestic double-zero foils. The reason is higher than abroad. To control the preferred grain size, to obtain a uniform microstructure, a fine grain of the blank can be used in the production of the appropriate amount of Al-Ti-B grain refiner grain refinement. The size of the compound in the aluminum foil should be controlled between 0.001 and 0.005mm. If it is too large, the source of cracks will be easily formed and the crack will expand to form pinholes. If the size is too small, the work hardening rate will increase. 1.2 The effect of metallurgical quality on the number of pinholes in aluminum foil The metallurgical quality of aluminum foil blank mainly refers to its quality. The quality of the quality of casting and rolling depends on two aspects: First, it is involved in foreign matter such as dust and large particles during casting and rolling. Material, in the rolling process will lead to pinholes; second, casting inclusions, bubbles and oxide film. As the rolling thickness is reduced, the bubbles crush into pinholes, inclusions, oxide films, etc. will fall off from the very thin aluminum foil surface to form pinholes. Therefore, the aluminum melt must be purified to enhance filtration, degassing, and slag removal. 2 Effect of aluminum foil production process on pinhole degree The rationality of cold rolling process has a direct impact on the number of pinholes in aluminum foil. For example, the crown, surface roughness of the roll, the filtering accuracy of the rolling oil, the rolling speed and the back tension control, and the annealing process are the main factors affecting the pinhole number of the aluminum foil. 2.1 Influence of the crown and surface roughness of the roller on the pinhole of the aluminum foil Pinholes appear at the lateral ends or in the middle of the foil when the roller profile is large or small, so the appropriate roller crown should be selected to reduce the pinhole. Occurrence rate. The roller surface is too rough, the rolling speed is high, and it is easy to cause broken belts. Moreover, there are many pinholes and the surface finish of the aluminum foil is low. When the surface roughness of the roller is small, the rolling speed is slow, which affects the productivity and increases the cost. In order to ensure the stability of aluminum foil production and product quality, and reduce the number of pinholes, it is stipulated in the production that the surface roughness of the rolling stick is 0.05-0.1 μm, the surface roughness of the finishing roll is controlled at 0.02-0.03 μm, and the entire roll is made as far as possible. Roller surface roughness is uniform. 2.2 Influence of aluminum foil rolling oil on pinhole degree Rolled oil plays a role of bearing, washing, cooling and lubricating in the production of aluminum foil. The main reason for forming pinholes in aluminum foil when the size of the particles in the rolling oil is larger than 10 μm. The main means of removing these particles is filtration, and the proportion of rolling oil should be reasonably adjusted so as to ensure the filtering accuracy of the rolling oil, and the viscosity can not be too large. As a result, the surface roughness of the aluminum foil is increased and pinholes are easily generated when filtering; Avoid the backflow of dirty oil. If the amount of rolling oil is insufficient during rolling, the foreign particles that fall into the foil surface will not be washed, and the lubrication will not be achieved. This will cause pin holes in the foil surface; replace the filter cloth regularly to avoid filtering. The impurities in the cake enter the net oil tank to pollute the net oil, causing the pinhole number of the double zero aluminum foil to increase or produce white bars; the oil temperature during the rolling process must not be too high, so as to avoid thinning of the rolling oil and poor lubrication, so that the rolling load increases rapidly. The rolling speed is increased, the oil thrown by the mill is severe, and the sticky aluminum phenomenon is increased, resulting in defects such as pinholes. 2.3 Effect of Rolling Speed ​​and Back Tension Control on Pinhole Degree When producing aluminum foil, the control of rolling speed and back tension (ie, unwinding tension) should be adjusted in conjunction with roll surface roughness and rolling oil properties. In particular, in the first pass and finished pass of the rolled product, whether the control of the rolling speed and the unwinding tension is appropriate has a great influence on the pinhole. When the rolling speed is too fast or the back tension is too large, the number of pinholes in the double-zero aluminum foil is significantly increased, resulting in a broken belt in severe cases. When the rolling speed is too slow or the back tension is too small, not only the productivity is affected, but also the aluminum foil is wrinkled, slits, and the like. 2.4 Influence of heat treatment process on pinhole degree The control of the size and number of coarse compound particles in heat treatment can effectively reduce the pinhole rate, improve the plastic processing performance and the quality of aluminum foil products. The heat treatment process is closely related to the control of the chemical composition and the alloy phase. On the one hand, the control of the alloy phase should cause Fe and Si elements to be precipitated from the aluminum matrix as much as possible, and exist as a second phase compound in the aluminum matrix; on the other hand, The type, shape, size, distribution, and quantity of item 2 should also be controlled through appropriate alloy design and process optimization. The production of double-zero aluminum foil involves many rolling processes and heat treatment processes from casting, cold rolling, intermediate annealing, foil rolling, etc. The organizational features of the former link will inevitably influence and influence the post process, and each process will influence each other. Restricted, isolated research and design process parameters or only consider one of the "main" links are one-sided, inadequate. Therefore, comprehensive consideration should be given to the heat treatment of aluminum foil production and the organizational changes and laws of the processing deformation process, and a rational and economical optimization process system should be formulated. Concluding remarks This article gives a comprehensive overview of the control of pinholes in the production process of double-zero aluminum foil. Appropriate boricing agent is used as a grain refiner to facilitate the control of pinholes. When the size of the particles in rolling oil is greater than 10 μm, The main reason for the formation of aluminum foil pinholes; annealing process is conducive to reduce the number of pinholes than the final product of aluminum foil. By controlling the above aspects, the number of pinholes of the double-zero aluminum foil is effectively controlled, and the quality of the ultra-thin aluminum foil is improved to solve the problems of the enterprise and improve the economic benefits.