Against the backdrop of the global lightweight and low-carbon transformation of high-end manufacturing, aluminum and aluminum alloy coils have become an indispensable key basic material for multiple pillar industries of the national economy, with their application scenarios continuously expanding toward high-end and refined directions, thanks to their core advantages such as low density, high specific strength, excellent corrosion resistance, recyclability, and excellent formability.
In the new energy and power battery sector, aluminum coils are the core supporting material for power battery systems. From stamped aluminum coils for battery shells, cover plates, and explosion-proof valves, to ultra-thin aluminum foils for tabs and current collectors, and high-strength aluminum strips for battery pack structural parts, the material stability and surface cleanliness of aluminum coils directly determine the safety performance and energy density of power batteries. In the food and pharmaceutical packaging industry, double-zero aluminum foil, can stock, and aseptic packaging aluminum coils, with their excellent barrier properties, light shielding, and food safety grade, have become the core carrier for food preservation and sterile pharmaceutical packaging, with extremely stringent requirements for the surface finish and shape accuracy of aluminum coils. In the aerospace field, 2xxx and 7xxx series high-strength aluminum alloy coils are the core materials for aircraft fuselage, wings, and landing gear structural parts, with military-grade strict standards for the consistency of mechanical properties and microstructure uniformity of the materials. In addition, in the fields of architectural decoration, electronic appliances, rail transit, and shipbuilding, aluminum coils have also become the core lightweight material replacing traditional steel products with their excellent comprehensive properties.
The end-use performance of aluminum coil products is fundamentally determined by two core processes: rolling and heat treatment. During the entire production process of aluminum coils, after plastic processing such as cold rolling and continuous rolling, the grains of the aluminum matrix will be broken, elongated, and lattice distorted, resulting in a significant work hardening effect. This is manifested in a sharp increase in the hardness and strength of the aluminum coil, a sharp decline in plasticity and elongation, accompanied by serious residual internal stress concentration. This not only fails to meet the requirements of subsequent deep drawing, bending, stretching, finish rolling and other processing procedures, but also causes defects such as deformation, cracking, and poor shape during subsequent processing and service. At the same time, residual rolling oil and lubricants during the rolling process will also affect the surface cleanliness of the aluminum coil and the effect of subsequent surface treatment.
As an indispensable core process in the production of aluminum coils, annealing heat treatment is the key link to solve the above problems and endow aluminum coils with the required service properties. Its core value is mainly reflected in five dimensions:
First, eliminating internal stress and stabilizing product dimensions. Through a precise heat treatment process, the residual internal stress accumulated during the rolling process is released, avoiding deformation and cracking of the aluminum coil during subsequent processing and long-term service, and ensuring the dimensional accuracy and stability of the product.
Second, softening the aluminum material and restoring processing plasticity. Through recrystallization annealing, the work hardening effect is eliminated, the elongation and formability of the aluminum coil are greatly improved, and the requirements of subsequent complex processing procedures such as deep drawing, bending and stretching are met.
Third, homogenizing the metallographic structure and stabilizing mechanical properties. By controlling the heating, holding and cooling processes, the grain size and precipitated phase distribution of the aluminum matrix are regulated, the microstructure homogenization is realized, and the deviation of core mechanical properties such as tensile strength and yield strength of the same batch and the same coil of aluminum is controlled within an extremely small range, meeting the stringent requirements of high-end fields for material consistency.
Fourth, completely removing residual rolling oil and ensuring surface cleanliness. During the annealing process, the rolling oil and lubricant remaining between the layers of the aluminum coil are taken away through high-temperature volatilization and hot air circulation, achieving a clean surface treatment without oil stains and yellow spots, laying a foundation for subsequent surface treatment processes such as anodizing, coating and laminating.
Fifth, realizing customized regulation of material properties. By adjusting the annealing process curve, the morphology and distribution of the precipitated phase of the aluminum alloy can be specifically regulated, and different strength, plasticity and corrosion resistance of the aluminum coil can be given to meet the customized needs of different end application scenarios.
It can be said that the process accuracy and execution effect of annealing heat treatment directly determine the final quality and application upper limit of aluminum coil products. The annealing furnace equipment with excellent performance is the core hardware foundation for realizing the precise annealing process and ensuring the quality of aluminum coil products.