Study on the Brazing Process, Microstructure and Mechanical Properties of 304 Stainless-steel Soundproof Honeycomb Core Sandwich Panels
DENG Yunhua1, YUE Xishan1,2, GUAN Zhichao1
1 Aeronautical Key Laboratory for Welding and Joining Technologies, AVIC Manufacturing Technology Institute, Beijing 100024; 2 School of Astronautics, Northwestern Polytechnical University, Xi’an 710072
Abstract: 304 stainless-steel soundproof honeycomb panel was brazed using BNi2 brazing filler metal. Microstructure and mechanical properties of present honeycomb panel as well as the effect of multiple brazing processes on the microstructure and mechanical properties were investigated. It was found that BNi2 brazing filler metal spread and solidficates on the surface of honeycomb core foils due to the capillarity effect. Notable atom diffusion was taken place between BNi2 brazing filler metal and honeycomb core foils. Brazing seam between face sheet and honeycomb core was consisted of Ni based solid solution structure with Cr, Si, etc, and no brittle intermetallic compounds. B and Si was migrated into face sheet which promoted the formation of reaction region between BNi2 brazing filler metal and face sheet, with grain boundary penetration characteristic due to the fast grain boundary diffusion behavior of B. With the increase of brazing thermal cycle times, the dissolution of brazing filler metal to honeycomb core foils and face sheets was improved and the grain boundary diffusion of brazing filler metal/face sheet zone was gradually intensive due to the increase of accumulated holding time at high temperature by multiple vacuum brazing. Tensile strength of present 304 stainless-steel soundproof honeycomb panel was 7.21 MPa, and all the tensile specimens were fractured at honey core region near face sheet. With the increase of brazing thermal cycle times, the tensile strength decreased. The flat compression strength, edgewise compression strength and bending strength of present 304 stainless-steel soundproof honeycomb panel were 5.67 MPa,33.85 MPa and 105.87 MPa respectively. Specimens of flat compression testing and bending testing encountered elastic deformation, plastic deformation and plastic instability during testing, while specimens of edgewise compression testing experienced plastic instability of honey core and peeling between perforated face sheet and honey core during testing. Considering the adverse effect of multiple brazing processes on the microstructure and mechanical properties of 304 stainless steel honeycomb panel, one repairing brazing was suggested for the subsequent repairing process of 304 stainless steel honeycomb panel.
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2018, Vol. 32 
