NiTi-Cu异种材料激光微连接机理及元素分布

Joining mechanism and element distribution in laser microweldingof NiTi-Cu dissimilar alloys

为实现NiTi形状记忆合金电致热驱动的功能特性,采用激光微连接技术对NiTi丝和铜板异种材料进行焊接,并利用光学显微镜、能谱分析仪等手段分析连接界面的微观结构和元素分布.基于ANSYS Fluent软件建立NiTi-Cu异种材料激光微连接三维计算流体力学仿真模型,分析了NiTi-Cu激光微连接过程中的温度场、流场演变和元素传输规律.结果表明,NiTi-Cu激光微连接过程主要分为激光在NiTi丝中的“钻孔”过程、对铜板的预热过程和在铜板中的“钻孔”过程.Ni,Ti,Cu元素混合主要发生于激光对铜板的“钻孔”过程中,元素在金属蒸气反冲压力和Marangoni涡流的驱动下相互混合,Cu元素进入熔池易形成低硬度的Cu-Ti金属间化合物,降低了脆性的NiTi金属间化合物形成的可能性.试验和仿真结果吻合较好,为优化NiTi-Cu异种材料的激光微连接工艺提供了重要的理论支撑.

To satisfy the thermo-driven requirements of NiTi shape memory alloys in different industrial applications,NiTi wire and Cu plate were welded by laser micro-welding technology.The microstructure and element distribution of the weld were experimentally studied using optical microscopy(OM)and energy dispersive spectrometer(EDS).Based on ANSYS Fluent software,a three-dimensional(3D)computational fluid dynamics(CFD)model for laser micro-welding of NiTi-Cu dissimilar alloys was established to analyze the evolutions of temperature and fluid flow fields and the element transport mechanism.The results indicate that the process of laser micro-welding can be mainly divided into 3 procedures,namely the"drilling"procedure of laser in NiTi wire,the preheating procedure of laser energy on Cu plate,and the"drilling"procedure of laser in Cu plate.The mixing of Ni,Ti,and Cu elements mainly occurs in the drilling process of laser in Cu plate,where the elements are mixing well under the driven of the metal vapor recoil pressure and Marangoni vortex.The Cu content in the molten pool is helpful to form low hardness Cu-Ti intermetallic compounds(IMCs),reducing the possibility of the formation of brittle Ni-Ti IMCs.The experimental and simulation results are in good agreement.The research provides important theoretical support for optimization of the laser micro-welding of NiTi-Cu dissimilar alloys.