超声辅助泡沫Ni/Sn复合焊料低温钎焊超细晶Al合金接头连接机理研究

超细晶粒Al合金具有优异的综合力学性能，但是该合金在较高温度焊接时易发生晶粒的粗化及力学性能的弱化，使其工业化应用受到了一定的限制。采用Sn基钎料低温钎焊能避免Al合金晶粒粗化现象的发生，但是获得的接头结合强度较差。本项目提出采用开孔泡沫Ni来增强Sn基钎料层的强度，并通过超声波辅助无钎剂钎焊工艺来促进泡沫Ni/Sn复合钎料与Al母材之间的界面润湿及冶金结合。研究超声钎焊工艺参数及泡沫Ni尺寸参数对接头显微结构及力学性能的影响，探究接头显微结构与接头性能之间的内在联系，揭示超声波作用下泡沫Ni/Sn复合钎料与Al母材之间的界面润湿机理及冶金反应机理。本项目研究对制备高性能超细晶粒Al合金低温钎焊接头，以及深入理解声场作用下钎焊接头的界面反应行为有着重要的理论意义和工程应用价值。

Ultrafine-grained (UFG) Al alloys exhibit excellent mechanical properties. However, joining UFG Al alloys at high temperature may result in the creation of grain coarsening and mechanical properties deterioration, which confines the industrial application of UFG Al alloys. The grain coarsening may be avoided when Al alloys are low-temperature soldered with Sn-based alloys, but joints soldered with Sn-based alloys exhibit low strength. This project attempts to strengthen the Sn-based filler metal layer with open-cell Ni foam, and enhance the interfacial wetting and metallurgic bonding between the Ni-foam/Sn composite solder and Al substrate with the assistance of ultrasonic waves. Effects of soldering parameter and Ni foam size on the microstructure and mechanical properties of Al alloy joints will be investigated. The relationship between microstructure and mechanical properties of Al alloy joints will be studied. The interfacial wetting and metallurgic reaction mechanisms between the Ni foam/Sn composite solder and the Al substrate will be revealed. The methodology and understanding developed in this project are helpful to fabricate high-performance UFG Al alloy joints soldered at low-temperature, and to further make clear the interfacial reaction behavior of soldered joints exposed to ultrasonic waves.