Study On Process And Mechanical Properties Of The Thin-core Aluminum Honeycomb Panel Prepared By Atmosphere Protect Brazing

Honeycomb panel is a kind of bionic composite material originated from natural honeycomb.Aluminum honeycomb panel has a series of advantages such as excellent specific strength,specific rigidity,super high stability,fire resistance,sound insulation and heat insulation.Due to these advantages,aluminum honeycomb panel is widely used in energy-absorbing boxes of passenger cars,bulkheads and floors of rail cars,interiors and compartments of ships,ceilings and curtain walls of buildings,and even wings of aircraft and satellites fairing.With the increasing requirements for the performance of honeycomb panels,the insufficient performance of GAHP(glued aluminum honeycomb panel)due to its adhesive has become more and more prominent.It is a feasible technical solution to use the welding method with the strong metallurgical bonding instead of the glued connection.In the demand of lightweight,honeycomb panels will inevitably have larger grids and smaller wall thicknesses as far as possible under the premise of meeting performance requirements.However,the thinner the honeycomb wall is the more defects such as erosion are easily to occur during the brazing process,so it has a relative narrow process window.Vacuum brazing technology can better solve this problem.However,the production cost of vacuum brazing technology is high and vacuum brazing technology is restricted by the size of the furnace,making it difficult to produce large honeycomb structures such as wall panels and blades.It has especially significance to develop the atmosphere protect brazing technology of aluminum honeycomb panel,which has a lower cost and smaller size limit.In this paper,the brazing process and performance of thin-core(0.1 mm)aluminum honeycomb panels were studied using atmosphere protect brazing technology.Aiming to find an atmosphere protect brazing process for the thin-core aluminum honeycomb panels to replace the costly vacuum brazing process.The results of this research include:(1)The spreading and wetting rules of the flux was studied,and the results showed that the best brazing temperature with the flux activity was about 610 ?.The change rules of the structure and performance of the substrate and the joint under different process parameters were analyzed.The influence of process parameters on the precipitated phase,solder residual layer,microhardness and grain size of the panel was discussed.The circle approximation method was used to evaluate the brazed joints,and it was found that even under the same process parameters,there are differences in the joint forms at different positions on the honeycomb wall,and a temperature difference hypothesis to explain this phenomenon was proposed.According to the continuity of the wall plate in the joint,the joints are divided into two types,and the change trends of those two types of joints under different process parameters are summarized respectively.Single and double wall flat joints were prepared by different process parameters,which the length was 60 mm.And the influence of brazing temperature and holding time for the mechanical properties of those two joints was discussed.Comprehensive consideration of various factors,the process window of atmosphere protect brazing of the thin-core aluminum honeycomb panels was tested.The process parameters of the BAHP(brazed aluminum honeycomb panel)were finally determined as the furnace temperature of 600 ?,and the holding time of 15min;(2)The mechanical properties of the BAHP prepared with the optimized process parameters and the GAHP in the same specifications was studied and compared.And the reasons for the differences were analyzed.The results showed that under the same honeycomb specifications,the BAHP has better flat stretch,flat compression,shearing and roller peeling properties than the GAHP.However,due to the thermal cycle of the brazing process,the tensile/compressive elastic modulus and shear elastic modulus of the BAHP are lower than the GAHP.The research provided a reference for the selection of using BAHP or GAHP.(3)The aluminum honeycomb panel has a complex internal structure,and also has a more complicated temperature and stress distribution during the brazing process.Abaqus software was used to analyze the temperature and stress field in the brazing process of thin-core aluminum honeycomb panels.The numerical simulation results are consistent with the test results.The hypothesis that there is a temperature difference at the joints of the single-wall and double-wall positions during the brazing process was confirmed.This research provide a reference for optimizing the brazing process and clamping method of aluminum honeycomb panels.