集磁器结构对磁脉冲辅助半固态钎焊接头组织和性能的影响

Effect of field shaper structure on microstructure and properties of magnetic pulse assisted semi-solid brazing joint

采用电磁-结构-流场耦合的多物理场耦合模拟方法,对比分析了等内径和带锥角两种集磁器条件下Cu/Al管的磁脉冲辅助半固态钎焊过程,考察了外管的变形行为和半固态钎料的剪切流变行为.结果表明,采用等内径集磁器时,钎料所受的剪切应力和相应的剪切流变速率在端部最高,底部次之,中部最弱,导致搭接区域内去膜效果存在差异,甚至影响界面冶金结合;而带锥角集磁器能更为合理地满足无钎剂钎焊对外管变形与钎料剪切流变的协调性需求,有效改善钎料流变行为,使剪切应力、剪切流变速率及去膜效果在整个搭接区域相对均匀,有利于提高界面连接质量.基于分析结果设计制造了改进的集磁器,进行了钎焊试验及相关测试分析.结果表明,相较于等内径集磁器,带锥角集磁器能有效改善Cu/Al接头的界面连接质量,细化搭接区域中部纤缝组织,并最终提高钎焊接头的抗剪强度.

The magnetic pulse assisted semi-solid brazing process of Cu/Al tubes with constant diameter field shaper and cone angle field shaper was analyzed by adopting the method of multi-physics coupling simulation of electromagnetic, structure and flow fields. The deformation behavior of outer tube and the shear flow behavior of semi-solid solder were investigated. The results shown that, the shear stress and corresponding shear flow velocity of solder were the highest at the top,followed by the bottom and the weakest in the middle by using constant diameter field shaper, which leads to the difference in removal of oxide film in overlap area, and even affects metallurgical bonding at the interface. The cone angle field shaper can more reasonably meet the requirements of the coordination between the deformation of outer tube and the shear rheology of solder without flux brazing, effectively improve the rheology behavior of solder and make the shear stress, shear flow velocity, removal effect of oxide film relatively uniform in the whole overlap area, which is beneficial to improve the quality of interface connection. Based on the analysis results, an improved field shaper was manufactured, and the brazing experiment and related tests were carried out. The results shown that,compared with constant diameter field shaper, the cone angle field shaper can effectively improve the interfacial bonding quality of Cu/Al joint, refine the grain of brazing seam, and finally improve the shear strength of brazing joint.