| Magnesium alloys are considered as the new ideal engineering material for 21 th century due to their high specific strength and stiffness,low densities, strong electromagnetic shielding, good damping and shock absorption, which have been widely used in the aerospace components, automobile industy, communication and computer parts.However, it is the poor wear and corrosion resistance that limits its extensive applications. It is rather difficulty to improve the wear and corrosion resistance of the whole material by smelting process due to the corrosion and wear is the behavior on the surface of the material.To improve the surface of the material performance is the best direct and effective method solving the problem of corrosion and wear.This study uses the method of plasma spraying and laser remelting to prepare the Ni based WC composite coating on the surface of AZ91 D magnesium alloy, Finite element models for analyzing the temperature field in laser remelting Ni based WC composite coating prepared by plasma spraying were established by ANSYS, and the effects of various process parameters on the temperature were studied, analyzing the microstructure and mechanical properties of the coating, laser remelting process parameters and coating properties prediction model is established based on support vector regression. The major completed tasks are as follows:1. Computational model is established for analysis of laser remelting temperature field which the program prepared by the APDL language is attached to the commercial software ANSYS. And this model is used in computing and analyzing the heating and cooling patterns in laser remelting process.2. The microstructure of the coatings have been characterized by SEM and XRD.Results show that the plasma spraying coating is a typical lamellar structure which the mechanical bond between the substrate and the coating is mechanical combination, after laser remelting processing, the coating and substrate from mechanical combination to metallurgical bonding and the coating surface present very smooth.WC particles in the high temperature decomposition, the decomposition of C elements react with Cr, Fe and Ni element to generate new compounds. after laser remelting, WC further decomposition, the C elements after reaction with Cr, Fe and other elements fully generated new hard phase,which could further improve the coating hardness and wear resistance.3. The tribology and corrosion resistance of the coatings are analyzed by the microscopic hardness tester, friction and wear tester and electrochemical workstation, at the same time the wear mechanism are discussed. Results show that the microhardness of laser remelting and plasma spraying layer is about 14 and 11 times higher than matrix,respectively. the wear resistance of laser remelting layer is higher than plasma spraying,which has good anti-friction effect, the wear mechanism of the plasma spraying and laser remelting layer are mild abrasive wear and the matrix wear mechanism is serious abrasive wear and adhesion wear, the corrosion potential of laser remelting and plasma spraying layer has increased by 0.322 V and 0.371 V compared with the AZ91 D magnesium,, which the corrosion resistance are improved greatly.4. The support vector regression(SVR) approach based on the particle swarm optimization(PSO) for its parameter optimization was proposed to predict the microhardness of AZ91 D magnesium alloys under different processing parameters including laser power, scanning speed and light spot diameter. The results showed that the better function approximation ability and the stronger generalization ability achieved by PSO-SVR is more accurate than that of SVR for identical training and test samples, the forecasting maximum relative error is 6.05% and 2.01% of SVR and PSO-SVR, respectively. |
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