Structure And Performance Of The Drawn Ni-coating Steel Strip Surface And Interface Section

Deeply drawing steel strip with electro-deposited nickel coating is a good material used in high-quality cell shell. The distrubution of electro-deposited nickel coating in the deeply drawing steel strip should be uniform and the coating should firmly adhere to the substrate. The coating's structure should be tight and its porosity ratio should be low. The corrosion-resistance and plasticity of the electro-deposited nickel coating should be good. The transition-layer of Ni and Fe at the interface was grown by vacuum heat-treatment. After that, the surface crystal grain was fined and molten to fill some holes due to the thermal shock of laser beam. In this case, the corrosion-resistance of the coating was improved.By appropriate heat-treatment method, we could obtain the transition-layer of Ni and Fe which resulted in the interface firmly metallurgy bond. On the other hand, the thickness of the transition-layer shoud be suitable. If the layer is thick, the iron will expose too much on the surface and the corrosion-resistance will be low. The electron-probe was used to measure the concentration curve of iron and nickel. The diffusion coefficient was obtained by fitting method. Firstly, we assume that the diffusion coefficient is independent on the concentration. According to the experimental result, we use the model of infinite diffusion couple and utilize the error solution of diffusion equation to fit the experimental results. The Ni and Fe mutual diffusion coefficients were obtained. Secondly, based on the assumption that the diffusion coefficient is dependent on the concentration, we don't use the commonly-used Boltzman-Matona method but utilize the least square method to fitthe experimental data and get the concentration curve equation. From the concentration curve equation, the concentration-dependent mutual diffusion coefficient was obtained. Combination with the iron and nickel phase graph, we also can know the phase structure of the interface. The results of X-ray diffraction proved the existence of these phases.Nickel coatings on the steel strip are cathodal coatings, and the hole erode is the main erosion mode. The holes of the exterior coatings were molten down partly by the pulse laser thermal shock. In this case, the quality of corrosion resistance could be improved. When the laser beam with high-energy scans the specimen quickly, the coating's exterior layer absorbs the energy and its temperature can attain to the phase transition temperature. The heat exchange of self-cooling quenching realizes the exterior nickel-coatings phase transition hardening. The alternating current impedance was used to examine the corrosion resistance. It is found that laser thermal shock improved the corrosion-resistant of the deeply drawing steel strip with Ni-coating. The laser thermal shock wouldn't affect the substrate crystal grain and can ensure enough plasticity for punching-molding as the improvement of the corrosion-resistance simultaneously.There are seven mechanical steps for the deeply drawing steel strip with electro-deposited nickel coating to be a battery cell. It is necessary to know the stress-strain relationship in the numerical simulation of the punching process. The stress-strain curve of electro-deposited nickel coating was determined. In this master thesis, a new method was proposed to determine the stress-strain relationship of the coating. The stress-strain relationship of the substrate /coatings composite and substrate were measured. After that, the stress-strain relationship of the coatings could bedetermined by a simple theoretical model. The cracks initiation and propagation could be observed in situ by scanning electron microscope in the deformation of the coating.