镀锡银钎料扩散过渡区的物相和形成机制

Phase Composition and Formation Mechanism of Diffusion Transition Zone for Silver-based Brazing Alloys with Tin Coatings

采用温度梯度法对镀锡银钎料进行热扩散处理,形成了扩散过渡区。为了揭示镀锡银钎料扩散过渡区的形成机制和主要物相的形成过程,借助金相显微镜、扫描电镜(SEM)、能谱分析仪(EDS)、X射线衍射分析仪(XRD)对扩散过渡区的显微组织、Sn元素的面扫描分布、物相组成及形貌进行分析。研究表明,Sn元素在镀锡银钎料中分布均匀、无偏析,在扩散过渡区主要以棒状Ag_3Sn相和块状Cu_3Sn相存在。随着热扩散温度升高,Ag_3Sn相和Cu_3Sn相的相对衍射强度逐渐增大。Ag_3Sn相的形成过程分为三个阶段:Ag_3Sn颗粒相弥散分布、Ag_3Sn颗粒相互相接触合并、生成大块棒状化合物相。Cu_3Sn相主要是锡晶须生长冲破镀层的氧化膜,在张应力和压应力协同作用下形成。镀锡银钎料扩散过渡区的形成机制为"钎接、互扩散、亚稳态、合金化"。

Silver-based brazing alloys with tin coatings were thermally diffused using temperature gradient method, and diffu- sion transition zone would occur. In order to reveal the compound phases and its formation process of silver-based brazing alloys with tin coatings, the mierostrueture, mapping images of Sn, phase and morphology of diffusion transition zone were analyzed using the metallurgical microscope, scanning electron microscope （SEM）, energy dispersive spectrometer （EDS） and X-ray diffractometer （XRD）, respectively. The results show that Sn are uniformly distributed in the diffusion transition zone. The microstructure of dif- fusion transition zone are mainly composed of AgaSn phase and CuaSnphase. The relative diffraction intensity of AgaSn phase and Cua Snphase gradually increase with the increase of diffusion temperature. The formation process of Aga Sn phase can be divided into three stages, including Aga Sn particle phase disperse distribution, Aga Sn particle phase merging and AgaSn bulk compound phase generation. Because the coating oxidation is broke out through tin whisker growth and synergistic action is formed between tensile stress and compressive stress, Cua Snp phase will be appeared at the diffusion transition zone. The formation mechanism of diffusion transition zone can he summarized as brazing, mutual diffusion, metastability, alloying.