Residual Stress In The Drawn Steel Strip With Electrodeposited Nickel Coating And Effect Of Laser Thermal Shock

With the development of science and technology, the applications of the electrodeposition technology have being transferred from decoration and protection to the functionally applied field. The electrodeposited coatings are widely used, the high properties of the coatings are also needed. Therefore, the study on the properties of the coating, especially the mechanical properties, is becoming a more important subject. Residual stress in the electrodeposited coating is inevitable, which has strongly effect on the properties during the service. The residual stress exits at the interface between the film and substrate, and may lead to the degradation, or delamination or completely failure of the coating. Therefore, the residual stress has attracted great interest in the research field. In the master thesis, the residual stress in the electrodeposited nickel coating on the drawn steel strip and other mechanical properties are investigated. The pulse laser beam was Nd:YAG laser with wave lenth of 1.06 JUJn and adjustable frequency. The effect of the pulse laser beam on the mechanical properties of the samples are discussed.In the Introduction, the application of nickel coating, the development of the residual stress in the electrodeposited coating and measurement methods of the residual stress are reviewed. According to nowadays aspect of the steel strip with electrodeposited nickel coating, the research of residual stress in the electrodeposited nickel coating is proposed.Firstly, the principal of electrodeposition and x-ray diffraction method to measure the residual stress were introduced. Secondly, a number of samples were prepared by adjusting the parameters, such as current density, thickness. The relationships between the residual stress and the parameters are investigated. Furthermore, the formation mechanism of the residual stress is discussed. In order to improve the properties of the coating, laser thermal shock and annealing were used toimprove the mechanical properties of the coating. The mechanism of the redistribution of the residual stress by laser thermal shock were analyzed. The microstructures and micrographs were studied by x-ray diffraction (XRD) and scanning electron microscopy (SEM). It was interesting that the residual stress after laser thermal shock had a new distridution compared to that before laser beam thermal shock. The residual tensile stress in original electrodeposited nickel coating would be changed as residual compressive stress. Nanoindenter was used to measure the Young's modulus and hardness of the coatings. The strain gradient plasticity explained the dependence of indentation depth on hardness and Young's modulus. The temperature field and the stress field during the laser thermal shock were simulated by finite element method (FEM). The results obtained by FEM is good agreement with the experimental results on the whole.