| In order to meet the requirements of battery shell of columned battery,electrodeposited Ni-Co coating on steel strip was treated separately under six differenttemperatures, especially for lithium ion power battery. We study the effect of the heattreatment temperature on the microstructure, anti-corrosion properties and mechanicalproperties of specimens, as well as the preliminary deformation mechanism of theelectrodeposited Ni-Co coating on steel strip. This provides experimental data andtheoretical guidance for industrialization production of electrodeposited Ni-Cocoating on steel strip. The main contents of this thesis were summarized as thefollowing aspects:(1) The multilayer Ni-Co coatings were electrodeposited on strap of punchingcold rolling carbon structural steel. And then the strips of different diffusion layerwere obtained under different heat treatment temperatures in protective atmosphere.(2) The microstructure morphologies of the heat treatment strips werecharacterized by XRD, SEM and EDS. The results show that the grain sizes of thespecimens increased gradually with the raising heat treatment temperature. Anickel/cobalt/iron diffusion layer is formed between the coating surface and substratewith (111)(200) double preferred structures. Without other texture are found clearlyafter heat treatment.(3) The corrosion resistance of specimens after the heat treatment was studied byusing Tafel extrapolation methods, Electrochemical Impedance Spectroscopy (EIS),and Neutral Salt Spray (NSS) test. The results show that the samples with the heattreatment650℃temperature and3h preservation held the most excellent corrosionresistance, maximum corrosion potential, minimum corrosion current. The range ofpassive potential was maximum and the spot rust in steel strip surface was minimum.(4) The mechanical properties of samples under different heat treatmenttemperatures were tested via Roughness Tester, Universal Tensile Tester andHardness Tester. The results show that the hardness of samples decreases as theraising temperature. However, the surface roughness changed a little. Especially themaximum elongation grown up to46%at the heat treatment temperature650℃.(5) The surface fracture morphologies of samples were characterized by in-situScanning Electron Microscopy (in-situ SEM) before and after heat treatment. The results show that the deformation behaviors of samples were quite different duringtensile deformation before and after heat treatment. As the tensile strain increasing,both the deposited layer and substrate stretched in samples after heat treatment,meanwhile the holes emerged, enlarged and expanded, whereas the cracks instead ofholes found in the samples without heat treatment.In summary, the electrodeposited Ni-Co coating on steel strip has very properhardness, elongation and yield ratio, with the corresponding heat treatmenttemperature being650℃and the preservation time being3h. The results show thatthe specimens have an excellent corrosion resistance in both acidity and alkalinitysolution after heat treatment. Meanwhile, the specimens have better mechanical andcorrosion resistance properties compared to existing products. Therefore, the shellstamped by the the electrodeposited Ni-Co coating on steel strip after proper heattreatment definitely meet the demands of lithium ion power battery. |
PDF Full Text Request