镁/铝异种金属超声辅助瞬间液相扩散连接机制研究

According to the lightweight needs in manufacturing industry the novelty method- ultrasonic-assisted transient liquid phase bonding (U-TLP) is used to join Magnesium/Aluminum dissimilar alloys as the joint embrittlement caused by IMCs is resolved by extrusion of excessive eutectic liquids. And the high strength Magnesium/Aluminum dissimilar joints can be obtained successfully within a few minutes without flux in atmosphere by using U-TLP method. First, the rule of acoustic induced plasticity in solid metal is studied and the removal mechanism of oxide film between solid interfaces is revealed. Second, the mathematical model of reaction kinetic of base metal and interlayer and numerical model of flow field analysis of reaction layer is set up. By means of adjusting the rule of interface reaction and flowing rule of liquid reaction layer the excessive eutectic liquids are extruded and the amount of IMCs are reduced remarkably, which helps to control the microstructure of joints. Third, the non-equilibrium solidification of the reaction layer is studied, and in particularly the research on the law of species, pattern and distribution of IMC in it is carried out. Finally, the fracture mechanism of Mg/reaction layer/Al joint is studied, and the corresponding relationship among U-TLP parameters, microstructure of joints and mechanical performance is set up. Aiming at hot spot- joining Magnesium/Aluminum dissimilar alloys the new technical method is approached and the relative theoretical and experimental foundation is provided through the implementation of this project.

针对制造领域中对轻量化的需求，本项目采用新方法-超声辅助瞬间液相扩散焊（U-TLP）实现大气环境下镁/铝异种金属无钎剂、低温、快速、高强度的连接，解决了因反应生成的金属间化合物（IMC）过多导致的接头变脆的问题。首先，揭示固态金属声致塑性规律及固/固界面氧化膜的去除机制。其次，建立中间层/母材动力学反应模型和声场激励作用下反应液相层的流动模型，通过调整界面反应规律与流场规律，有效挤出多余反应液相并降低钎缝中IMC比例，实现钎缝微观组织的可控连接。再次，研究声场、热场及流场复合作用下反应层的非平衡凝固规律特别是IMC的种类、形态及分布规律。最后，研究镁/中间层/铝U-TLP接头的断裂机制，建立U-TLP工艺参数（声学及钎焊）-接头组织-力学性能之间的响应关系。通过该项目的实施，为镁/铝异种金属的连接探索新的技术路径并提供相应的理论及实践基础。

镁合金与铝合金作为地球上储量最丰富的轻质金属，它们都被广泛应用在电子电器、汽车交通、航空航天、国防军工等领域来减轻构件重量。迄今为止，已采用激光焊、搅拌摩擦焊、钎焊和扩散焊等方法连接镁/铝异种合金。然而，在这些方法中，易产生Al3Mg2和Al12Mg17等脆性金属间化合物，导致接头连接性能较差。本项目首先搭建了超声辅助瞬间液相焊设备平台，通过该平台可以实现以下焊接参数：焊接温度范围：150-700℃，控温精度±1℃，超声波输出频率1kW，振动频率30kHz，振幅范围5-15μm，气压加压0-1.5 MPa。.采用以镍基及铜基复合中间层超声辅助瞬间液相扩散连接（U-TLP）MB8镁合金与2024铝合金，成功阻隔了镁、铝合金的直接接触，在大气环境下，380~400 ℃钎焊时获得了无缺陷、力学性能优良的MB8/2024异种金属接头。通过控制复合中间层的搭配形式，实现了以下的钎焊效果：（1）完全避免了了Mg-Al二元金属间化合物；（2）使镁合金及铝合金两侧的反应速度趋于一致，避免了镁合金的溶蚀；（3）有效调控了镁、铝合金两侧钎缝的物相；（4）钎缝剪切强度提升至95.3MPa（镍基）和85.3MPa（铜基）。