清洗工艺对GH4099蜂窝夹层结构钎焊性能的影响

Effect of Cleaning Process on Brazing Property of GH4099 Honeycomb Sandwich Structure

目的研究激光清洗和离子轰击对GH4099蜂窝夹层结构钎焊性能的影响,优化GH4099蜂窝夹层结构焊前清洗工艺。方法分别用400#砂纸、不同激光功率(60~200 W)、不同离子轰击时间(1~2 h)对GH4099带材表面进行了砂纸打磨、激光清洗和离子轰击试验,分析了激光清洗和离子轰击对GH4099表面形貌、O元素含量、BNi2钎料润湿性的影响,测试了不同清洗工艺下蜂窝夹层结构钎焊接头的拉伸性能。结果随激光功率从60 W增加到100 W,GH4099表面O含量逐渐降低,表面粗糙度逐渐增大,钎料润湿面积百分比增加到83.5%,润湿性增加。当激光功率大于100W时,表面残留网状分布的氧化物,导致钎料润湿性降低。当激光功率进一步增加到200 W时,氧化物网状分布现象减轻,润湿性随之增加,粗糙度也有所降低;随离子轰击时间从1 h增加到2 h时,带材表面氧化皮逐渐去除干净,钎料润湿性随之增加,钎料对离子轰击2 h的表面的润湿面积百分比达到91.2%,与400#砂纸打磨的相当。经离子轰击2 h、1020℃-15 min钎焊获得的夹层结构等效抗拉强度为11.9 MPa。结论与激光清洗相比,离子轰击可以同时去除蜂窝型面及附近侧壁部分的氧化皮,能更有效地改善钎料对蜂窝基体的润湿性。

Pre-welding cleaning process is of great importance for honeycomb sandwich structure to gain a satisfactory brazed joint.Due to the poor stiffness in plane direction of honeycomb core,the more effective cleaning method for honeycomb is non-contact cleaning,including laser cleaning and ion bombardment cleaning.The work aims to study the effects of laser cleaning and ion bombardment cleaning methods on brazing property of GH4099 honeycomb sandwich structure,and optimize the pre-welding cleaning process of honeycomb sandwich structure.The GH4099 strips were cleaned to remove oxide layers by polishing with 400-grit sandpaper,laser cleaning and ion bombardment respectively.Laser cleaning was performed on 200 W nanosecond fiber laser cleaning machine(HL200-RSP2)with the frequency of 2000 Hz,and scanning speed of 7000 mm/s,and laser power varying from 60 W to 200 W.Ion bombardment cleaning was performed on homemade surface activation/joining combined forming equipment.The cleaning time was varied from 1 h to 2 h with cleaning power of 100 W and acceleration voltage of 200 V and vacuum pressure of 1.6 Pa.Characters of morphology,roughness and O element content of the cleaned strip surface were detected by using stereo microscope(ZEISS,SteREO Discovery.V8),surface roughness measuring instrument(Mitutoyo SJ-210)and scanning electron microscope(FEI Nova 450);BNi2 brazing filler metal foil with thickness of 0.05 mm was cut into squares with size of 10 mm×10 mm,and wettabilities of BNi2 foils on cleaned surfaces with different cleaning processes were characterized by brazing wetting test.The cleaning parameters were optimized by the comparative analysis of these test results.Then honeycombs were cleaned at the optimized parameters of laser cleaning and ion bombardment respectively,and honeycomb sandwich structures were brazed.Both wetting test and brazing process were performed in the joining chamber of surface activation/joining combined forming equipment at the temperature of 1020℃for 15 min with vacuum pressure less than 5×10-3Pa and heating rate of 10℃per minute.And samples were cooled to room temperature with furnace after brazing.Tensile properties of brazed joints of honeycomb sandwich structure with different cleaning methods were tested on CMT 5504 tensile test machine at tensile speed of 1 mm/min.Microstructures of brazed joints and fracture morphologies of tensile test specimens were examined by using stereo microscope and SEM respectively.Results show that the mean content of O element of surface decreased and wettability of filler metal increased with the increasing of laser power,and wetting area fraction increased to 83.5%when laser power increased to 100 W.While the wettability of filler metal decreased since there were residual reticulated oxide on the strip surface when laser power higher than 100 W.With the laser power increased to 200 W,residual reticulated oxide was reduced.With the cleaning time of ion bombardment increased from 1 h to 2 h,oxide layer on the strip surface was gradually removed,and wetting area fraction reached to 91.2%with the cleaning time of 2 h,which was corresponding to that on the surface polished by 400-grit sandpaper.Honeycomb sandwich structure cleaned by ion bombardment for 2 h and brazed at 1020℃for 15 min had the highest tensile force,and the equivalent tensile strength was 11.9 MPa.Compared to laser cleaning,ion bombardment can remove the oxides on the honeycomb surface and the nearby side wall simultaneously,and improve the wettability of filler metal to the honeycomb matrix more effectively.