304不锈钢消音蜂窝钎焊工艺、组织及力学性能分析

采用镍基BNi2钎料钎焊制备了304不锈钢消音蜂窝,对蜂窝芯体与面板钎焊界面组织和蜂窝的力学性能进行了分析和测试,并研究了钎焊热循环次数对钎焊界面组织和蜂窝拉伸力学性能的影响,为实际工程应用确定未焊合缺陷补焊次数提供了依据。液态钎料的毛细作用使钎料沿蜂窝芯箔材表面铺展并与箔材发生显著的元素扩散反应,蜂窝芯与面板之间的钎缝由Ni、Cr、Si等互溶而成的Ni基固溶体组织组成,未生成脆性共晶组织或金属间化合物。钎料中的B和Si元素显著扩散于面板材料中,形成钎料-面板反应区,因B元素的沿晶界快速扩散效应,面板侧组织呈现晶界元素渗入特征。随着钎焊次数增加,钎料对母材的溶解和晶界渗透增加,钎焊界面组织发生显著变化。制备的304不锈钢消音蜂窝拉脱强度为7.21MPa,呈现板/芯界面附近蜂窝芯破坏特点,多次钎焊时蜂窝拉脱强度呈下降趋势。制备的304不锈钢消音蜂窝平压、侧压和弯曲力学性能测试过程均经历弹性变形、塑性变形和失稳三个阶段,强度值分别为5.67MPa、33.85MPa和105.87MPa,平压和弯曲失效模型为蜂窝失稳,侧压破坏除蜂窝失稳外,发生穿孔面板与蜂窝芯体剥离的现象。鉴于多次钎焊热循环对蜂窝拉脱强度的不利影响,建议304不锈钢蜂窝钎焊缺陷的最大补焊次数为一次。

Study on the Brazing Process, Microstructure and Mechanical Properties of 304 Stainless-steel Soundproof Honeycomb Core Sandwich Panels

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.