基于同步辐射与第一性原理计算的Al/Cu钎焊界面组织与接头性能研究

Study of the Interfacial Microstructures and Properties at the Al/Cu Brazing Joints by Using Synchrotron Radiation and First-principles Calculations

界面脆性化合物对Al/Cu钎焊接头力学性能影响显著,明晰界面化合物的形成、生长行为与块体性质对调控界面组织与接头性能至关重要。本文借助同步辐射X射线成像技术对加热与冷却过程中Al/Cu钎焊界面组织演变进行动态表征,利用第一性原理计算对界面化合物的块体性质进行计算,研究了界面化合物的形成次序、模量与键合特征。结果表明,界面Al_(2)Cu与Al_(4)Cu_(9)化合物在冷却过程中形成,小平面枝晶状Al_(2)Cu化合物为初生相,从原始界面处凝固析出,且二次枝晶臂呈非对称性;与母材接触后发生扩散反应形成层状Al_(4)Cu_(9)化合物。界面化合物具有金属键与共价键的混合键合特征,Al_(4)Cu_(9)化合物具有较高的结合能、体积弹性模量、剪切模量、杨氏模量与硬度,可提高Al/Cu钎焊接头硬度,降低塑韧性。

Interfacial brittle compounds strongly affect the mechanical properties of Al/Cu brazing joints.It is important to determine the formation,growth behavior and bulk properties of interfacial compounds to further control the interfacial microstructures and properties of joints.In this paper,synchrotron radiation X-ray imaging was used to dynamically characterize the interfacial reactions at Al/Cu brazing joints,and first-principles calculations were subsequently performed to calculate the bulk properties of the interfacial compounds.The formation sequence,modulus and bonding characteristics of the compounds were investigated.The results show that layered Al_(4)Cu_(9)and faceted and dendritic Al_(2)Cu compounds form during cooling.The faceted and dendritic Al_(2)Cu compound is the primary phase and precipitates at the original interface,exhibiting the characteristics of asymmetric secondary dendrite arms.After the Al_(2)Cu compound contacts the base metal,the Al_(2)Cu compound reacts with the base metal to form the Al_(4)Cu_(9)compound.The interfacial compounds exhibit mixed bonding characteristics,including metallic and covalent bonding.Compared to those of the Al_(2)Cu compound,the Al_(4)Cu_(9)compound has a greater cohesive energy,bulk modulus,shear modulus,Young's modulus and hardness,enhancing the hardness of the joints and decreasing their toughness and plasticity.