Research On High-Frequency Induction Brazing And Tig Welding Process Of Low-Power Hall Thruster

In recent years,micro-satellites have developed rapidly.Faced with the problem of limited power provided by micro-satellites,it is necessary to design low-power propulsion systems for them.The low-power Hall thruster has a simple structure and a large thrust-to-power ratio.It is a reasonable choice for a micro-satellite propulsion system.However,due to the small parts and compact structure of the low-power Hall thruster,and the entire part is in the magnetic field generated by strong magnetism,the heat input needs to be strictly controlled during the welding process of the Hall thruster parts,and the influence of the magnetic field on the welding process needs to be solved.Therefore,the welding method originally used for the Hall thruster is no longer applicable.Therefore,it is necessary to design a suitable welding scheme for the low-power Hall thruster and design the corresponding welding process.High-frequency induction brazing is particularly suitable for welding thin-walled stainless steel pipes due to the use of split-and-combination induction coils,while TIG welding has relatively high weld strength due to its fusion welding method.In this paper,Ag₇₂Cu₂₈ eutectic filler ring is used to insert a 1Cr18Ni9Ti pipe with an outer diameter of 2mm and an inner diameter of 1mm into a 1Cr18Ni9Ti plate with an aperture of 2.20±0.05mm to perform high-frequency induction brazing on the tail part of the anode inlet pipe of the Hall thruster.Using 1Cr18Ni9Ti welding wire to perform TIG filler wire welding on the part where a 1Cr18Ni9Ti casing with an outer diameter of 5mm,an inner diameter of 3mm,and a height of 2.5mm was lapped with a 1Cr18Ni9Ti pipe with an outer diameter of 3mm and an inner diameter of 1mm.For the high-frequency induction brazing brazing seam at the tail of the anode intake pipe,there are no macroscopic cracks,unfilled,loose,etc.,and the brazing angle is 9.08°.Microscopically,when the high-frequency induction heating time is50s and 60s,there is a distribution of Ag-rich phase/Cu-rich phase/1Cr18Ni9Ti at the edge of the brazing joint.When the high-frequency induction brazing time is 70s,a diffusion layer appears on the surface of the 1Cr18Ni9Ti base metal.The main elements in the diffusion layer are Ag and Fe,and the thickness is about 2?m.When the high-frequency induction brazing time is 90s,the diffusion The thickness of the layer reaches about 6?m.With the increase of high-frequency induction brazing time,the tensile properties of the welded joints gradually improve,and the rate of increase gradually slows down.When the high-frequency induction brazing time is more than80s,the tensile part breaks at the base material.The fracture mode of different high-frequency induction brazing time is ductile fracture.With the increase of high-frequency induction brazing time,the dimples at the fracture site gradually become larger,deeper and more numerous.For the TIG weld on the head of the anode intake pipe,when the welding voltage is 13V,the welding time is 2s,and the welding current is 24A,a welded joint with sufficient metallurgical bonding,uniform weld formation,and certain strength can be obtained.As the welding current increases,the mechanical properties of welded joints first increase and then remain flat,reaching the maximum value when the welding current is 26A,which is 112.5%(225HV)of the base metal.For the best parameter of welding current 24A,the microhardness is 108.7%(217.4HV)of the base material.A tensile test was carried out,and it was found that all fractured at the base material ceramic,the average tensile strength was 24.25MPa,and the corresponding maximum tensile force was 1123.9N.The microstructure analysis of TIG welds reveals that the welded joints have four types of microstructures.The first type of structure is a structure with many fine austenite grains and some delta ferrite dendrites,mostly in the middle of the weld;the second type of structure is a structure between dendritic ferrite and dendrites The mixed structure composed of fine austenite mostly exists at the edge of the weld;the third is the structure composed of austenite and ferrite grown on its grain boundaries,which exists in the re-melted and large amount of melting In welds;the fourth type is a fully austenite region composed of cellular crystals,which exists in welds that are remelted and less melted.