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激光焊接试验中选用板式换热器常用的0.7mm纯镍Ni201薄板,其具体化学成分和机械性能分别如表 1和表 2所示。利用线切割机床将纯镍Ni201薄板切割成50.0mm×20.0mm×0.7mm的尺寸用于激光焊接试验,焊接前,用丙酮超声清洗,除去试件表面的油污及脏污。
Table 1. Nominal chemical composition (mass fraction) of pure nickel Ni201
C Si Mn S Cu Fe Ni ≤0.0002 ≤0.0035 ≤0.0035 ≤0.0001 ≤0.00025 ≤0.0040 0.99 Table 2. Mechanical and physical performance parameters of pure nickel Ni201
material trademark tensile strength/MPa elongation/% thermal conductivity/(J·kg-1·K-1) resistivity/(μΩ·m) Ni201 420 40 67.3 950 激光焊接试验中使用DC050型板条式CO2激光器与SLC-X1530/1020四轴联动多功能数控机床,采用FAGOR8070系统实现机床的编程与控制。CO2激光器最大输出功率P=5.0kW,激光波长λ=1064nm,光束发散角极小,激光输出的光束模式为准高斯光束。自行设计了悬挂式旋转永磁体电磁搅拌装置,其可与激光头实时联动,永磁体产生的磁力线方向为水平方向,且以激光熔池中心线为轴呈对称分布。图 1为磁场辅助激光焊接示意图。
本试验中采用CO2激光器对纯镍Ni201薄板进行激光堆焊试验,焊接过程中对焊件进行双面混合气体保护,激光焊接工艺参量为:激光功率P=1.5kW,焊接速率v=600mm/min,离焦量Δf=0mm,焊接过程中采用氩气与氦气的混合气作为保护气体,氦气保护气体流量为10L/min,氩气保护气体流量为15L/min。试验过程中,旋转磁场转速ω=600r/min,调节磁场强度B分别为0mT, 30mT, 40mT, 50mT, 60mT, 70mT。
焊后在Ni201薄板上截取金相试样,并采用硝酸水溶液(20mL硝酸+20mL水)腐蚀剂对处理后的样件进行金相腐蚀。采用金相显微镜和扫描电子显微镜对接头显微组织形貌进行观测与分析。采用德国Zahner电化学工作站测定纯镍Ni201激光焊接接头的极化曲线,测试温度为25℃,测试过程采用三电极体系,工作电极为纯镍焊缝,辅助电极为铂片电极,参比电极为饱和甘汞电极,腐蚀介质是质量分数为0.035的氯化钠溶液。测量前,将工作电极浸入腐蚀介质中静置5min~10min,待工作电极稳定再对其进行极化曲线的测定。电位扫描范围为-1.5V~1.5V,电位扫描速率为10mV/s,在测试过程中,隔离整个测试系统,保证测试结果的准确性。
磁场对工业纯镍激光焊接组织与耐腐蚀性影响
Effect of magnetic field on microstructure and corrosion resistance of industrial pure nickel laser welding
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摘要: 为了研究磁场对激光焊接的影响,采用在焊件上方放置自制的悬挂式永磁体电磁搅拌装置提供横向旋转磁场的方法,对纯镍Ni201薄板进行了CO2激光堆焊试验。焊后采用金相显微镜和扫描电子显微镜进行观测与分析,并利用电化学工作站对焊接接头进行了电化学腐蚀试验。结果表明, 在不同磁场强度下,焊件均能完全焊透,焊缝成形良好,焊缝内部均为粗大的奥氏体柱状晶晶粒组成;磁场强度对激光焊接接头的宏观形貌影响不大;且随着磁场强度的增加,纯镍Ni201激光焊接接头的凝固组织逐渐细化,焊缝耐腐蚀性能逐渐提高;外加横向旋转磁场通过电磁搅拌作用促进熔池的传热和传质,增加过冷度,提高形核率,使晶粒细化,提高焊缝的耐腐蚀性能。该研究为旋转磁场辅助激光焊接技术的工业应用提供了参考数据与技术支持。Abstract: In order to study the influence of magnetic field on laser welding, a self-made suspended permanent magnet electromagnetic stirring device was placed above the weldment to provide a transverse rotating magnetic field, and a CO2 laser welding test was performed on the pure nickel Ni201 thin plate. After welding, metallographic microscope and scanning electron microscope were used for observation and analysis, and electrochemical workstation was used to conduct electrochemical corrosion test of welded joints. The test results show that, the weldments can be completely welded with different magnetic field intensity, and the welds are formed well, and the inside of the weld is composed of coarse austenite grain.The magnetic field intensity has little effect on the macroscopic appearance of laser welded joints.With the increase of magnetic field intensity, the solidification microstructure of pure Ni201 laser welded joint is gradually refined, and the corrosion resistance of weld metal is gradually improved. The external rotating magnetic field can promote the heat transfer and mass transfer in the molten pool by electromagnetic stirring, increase the supercooling, increase the nucleation rate, make the grain refined, and improve the corrosion resistance of the weld.
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Table 1. Nominal chemical composition (mass fraction) of pure nickel Ni201
C Si Mn S Cu Fe Ni ≤0.0002 ≤0.0035 ≤0.0035 ≤0.0001 ≤0.00025 ≤0.0040 0.99 Table 2. Mechanical and physical performance parameters of pure nickel Ni201
material trademark tensile strength/MPa elongation/% thermal conductivity/(J·kg-1·K-1) resistivity/(μΩ·m) Ni201 420 40 67.3 950 -
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