Study On Principle And Technique Of The Preparation Of Aluminum Honeycomb Structure By Middle Temperature Precision Self-brazing Process

Aluminum Honeycomb Panels have been widely used in aerospace, transportation and architectural fields because they have the advantages of low density, high stiffness, good stability, heat insulation and sound insulation. Currently most honeycomb structures are bonding by organic gel. The joint strength, heat resistance and aging resistance of the glued aluminum honeycomb panel cannot be greatly improved because of the limit of the adhesive performance. The brazing temperature of existing brazed aluminum honeycomb panel is too high for most heat-treatable aluminum alloys. Therefore, the study on the preparation of aluminum honeycomb structure by middle temperature brazing process will be very meaningful.In this paper, T-joint aluminum sheets and aluminum honeycomb cores were brazed with the middle temperature self-brazing flux. The interfacial reaction mechanism of the middle temperature self-brazing and the composition and microstructure of the joint were investigated. The tensile-shear tests of the brazed joint of aluminum honeycomb cores were carried out. The main research results include:?1? The middle temperature self-brazing flux was prepared by wet synthesis process. CsF-AlF3 binary eutectic flux was selected as the flux matrix and ZnCl₂, SnCl₂ were selected as the interfacial activation substance. The appropriate addition quantity of ZnCl₂ and SnCl₂ were less than 6%+6%. The optimal addition of ZnCl₂ and SnCl₂ were 4% +4%. At this addition level, the flux has good melting characteristics and flowability. Good brazed joints can be obtained.?2? The brazing seam of self-brazing T-joint was mainly Sn metal layer. During brazing process, Zn2+ and Sn2+ from the flux reacted with Al atoms at the interface. A liquid metal film was formed at the joint, forming brazing joint between base metals. Due to the great solid solubility of Zn in Al, the precipitated Zn quickly penetrated into parent metal. During solidification process only Sn along grain boundaries remained in the joint. The main defects in self-reactive brazed joints were slag, which were composed of flux residue and accumulated fragments of the oxide film. Annealing for brazed joints had little effect on the microstructure of the self-brazing joints. T-joint aluminum sheets of 0.5mm can be well brazed by self-brazing.?3?Aluminum honeycomb cores prepared by molding method were brazed at 570°C using the flux of e5+4%ZnCl₂+4%SnCl₂. There were no continuous metal layers in the honeycomb core brazed joints. Only discontinuous Sn layer was distributed in the brazing beam along grain boundaries. The growth of new grains at the interface of the brazing seam pushed part of Sn metal away from the seam. The typical defects in the joints were closed slag.?4?The tensile-shear strength of aluminum honeycomb core prepared using 1060 aluminum foil was 45-55 MPa. The tensile-shear strength of aluminum honeycomb core prepared using aluminum alloy brazing sheet was 70-90 MPa. After aging test at 200°C the tensile-shear strengths of two kind of aluminum honeycomb cores were not significantly decreased.