| The research was based on the improvement of the welding procedure of the combustion chamber in a liquid-propellant rocket engine. Choosing the appropriate filler material to get the lap joint of T2 copper and 304 stainless steel by means of the CMT technology. The phase formed on the interface, microstructure and mechanical properties of Copper-Steel welded joints were studied. Develop and optimize the welding procedure in consideration of the characteristics of temperature field distribution and the influence of welding parameters on the temperature field, to guide the welding of the actual component.Firstly, test with different welding wires and com pare the appearance and organizational performance of welds, the experimental results showed that S201 wire is the most suitable filling material. Further, reach the specification range of wire feeding speed, welding speed and welding torch angle by proces s experiments. The model of cubic regression equation between contact angle, the spreading width, tensile strength and welding parameters was built based on the response surface method(RSM). Analysis of the influence welding parameters cause on contact angle, the spreading width and tensile strength was made, it turned out that appropriate welding speed, slow wire feed speed with large angle of welding torch is easier to get excellent Copper-Steel welded joint. The optimal welding procedure was experimentally confirmed, which proved that the model above matches the practical situations well.Then, the interface and the welded zone of different joints were analyzed by means of optical microscope, SEM, and EDAX. The cooling speed is faster at the surface of steel and boundary of the molten pool, and the temperature gradient is larger at the surface of steel, so when the steel melted, the size of cellular crystal grow vertically from steel is small and the cellular crystal grow vertically from molten pool boundary to the weld center is coarse. In contrast, the supercooling degree in the upper of weld zone is larger, so there appeared equal-axed grains. The interface was comprised of α-Fe and ε-Cu. When the steel did not melt, iron will precipitate continuously in the process of cooling, there was a lot of diffuse distribution α-Fe, which promotes the process of heterogeneous nucleation. Therefore, weld zone was consist of fine equal-axed grains instead of cellular crystal. The interface was comprised of α-Fe. Fe3 Si generated in a small amount on the interface of the joint of S211.The fracture occurred in the heat affected zone, obvious necking was found in the tensile specimen, it’s a kind of ductile fracture, the tensile strength is 220.78 MPa and it reaches 76.89% of the base metal. The minimum hardness also appears in heat affected zone.At last, based on the comprehensive analyses of heat transfer behavior in the welding process, an entity model was established by using the actual size. The temperature field was simulated by using a double ellipsoid heat source. The simulation results was verified by comparison of the thermal cycle curves between calculated results and experimental results. The results obtained by the model were in good agreement with the experimental ones, isotherm is asymmetrical and change welding parameters will affect the temperature field distribution, increase welding wire feeding speed or decrease welding speed will result in bigger area of high temperature, and with the increase of welding torch angle, the main heat input gradually turns from copper to steel. |
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