Papers by Author: Y.S. Wang

Abstract: In order to improve the surface Performance of thick copperplate, A Ni- Cr alloy coating metallurgically bonded onto thick copperplate is performed by YAG laser remelting plasma spraying coating process. In laser cladding processing, it is difficult to get good metallurgical bonding between the layer and copperplate. Plasma spraying technology is developed to get a alloy layer on the surface of thick copperplate, and then using YAG laser cladding method to make a coating. The results of Micro organization analysis indicate that the cladding layer and substrate form favorable metallurgical bonding, as a narrow metallurgical bonding zone, about 3m in thickness. The structure is more compact compared with witch of plasma spraying coating, and the crystal grains are refined grain.

Abstract: The profile and temperature distribution of laser molten pool are mainly factors which have directly effect on quality of laser processing (laser melting and laser cladding). It is very necessary to study measurement method of melting process in laser molten poo1 on-line, for improving processing design and inspecting laser processing quality. A system of dynamic process measurement for laser molten pool was developed. The melting process of laser scanning molten pool formed by high power CO2 Laser was measured. Its temperature distribution was analyzed by special analysis software. It was shown that a section of integrated molten pool would come into being in the middle of the laser scanning line spot after a period of scanning time, and then the molten pool got increased in length with the time, and a little increased in width at the same time, the result was consistent with that of computer numerical simulation. Compared with laser focusing spot, laser scanning spot was more uniform in temperature distribution, that could be propitious to improve the quality of laser processing.

Abstract: Based on the calculation formulas of heat treatment temperature field of the narrow strip spot of laser beam passing a scanning rotating mirror, the effect of scanning frequency on temperature field was analyzed in this study, and the math model of the temperature field with scanning frequency was derived applying the superposing principle of the temperature field. The value simulation and figures description were given. The relationship between scanning frequency and temperature distribution was studied, and the best extent of frequency was given for carbon steel laser quenching with laser rotating mirror. The value simulation shows that the higher the scanning frequency is, the more evenly distributed the temperature field gets. At a certain laser power and a certain length of laser scanning line spot, for non-melting laser heat treatment under the spot, a maximum thickness of the high- temperature layer can be get at some certain scanning frequency range which depends on thermal diffusion coefficient of the material.

Abstract: In order to improve the wear resistance of the surface of thick copperplate, a coating of alloy powder is produced on the surface of the thick copperplate with the method of laser remelting plasma sprayed coating. The value simulation of temperature and the experimental results show that, it is difficult to produce ferronickel coating with large area and crackfree on thick copperplate for laser cladding technique. Using transsonic plasma heat spraying method to fix the alloy powder on the surface of thick copperplate, a sprayed coating can be produced, which has certain adhesion strength to the copperplate. In order to prevent crack produced in large area laser remelting coating, a method with band-like and point-like remilting area at intervals of same distance has been taken. The surface appearance and roughness of the coating produced by plasma spraying are compared with that of the coating produced by plasma spraying and remelted by laser, micro organization analysis and wear resistance comparison experiments are taken to the specimen. The microstructure photos show that the coating of the plasma heat sprayed is mainly made up by grains, with a great deal of pores existing. After laser remelting, microstructure of the coating is more compact, and the most of pores disappeared, so the strength of the boundary between the remelted coating and the copperplate is build up and the coating with large area and crackfree on thick copperplate is performed by the method of laser remelting plasma spraying coating in large amount of point-like remilting areas The experiment result shows that the wear resistance of laser remelting plasma heat sprayed coating enhances 3 times more than That of the unremelt coating, and about 14 times compared with the copperplate, and the wear resistance of the surface with point-like laser remelting area is between that of plasma heat sprayed coating and that of the laser remelting coating, it depends on the ratio of the remelted part to the whole in area, however, the wear resistance increases with the value of the ratio