A356合金二次无氰浸锌层的微观组织研究

本文利用扫描电镜（SEM）和原子力显微镜（AFM）观察了一次浸锌和二次浸锌不同时间下浸锌层的微观形貌，建立了无氰多元浸锌全过程模型。结果表明铝及其合金的浸锌过程是锌晶粒在基体上不断形核和长大的过程。浸锌初期主要是晶核形成期，浸锌后期主要是晶粒生长期；金属离子放电的高活性中心在金属表面上的低能量点上，多元合金中的铁、镍和铜是锌晶粒生长的异质晶核；二次浸锌得到的锌晶粒比一次浸锌更细小、均匀和致密，对基体覆盖能力好。二次浸锌时间为20-30S时，浸锌层的微观形貌最好。

Morphology of Secondary Non-cyanide Zinc Coating Layer for A356 Alloys

Morphology of the zinc coating layer by single and secondary zinc coating at different time was studied by SEM. The model of zinc coating process in non-cyanied polybasic zinc coating solution was established. Zinc coating process on Al and its alloys was shown to be the nucleation and growth of zinc crystals on the substrates. The early zinc coating process was the nucleation, and the later stage was the growth of zinc crystals. The low-energy points on the metal surface were the high-activity discharge areas of metal ions. Fe, Ni and Cu in polybasic solution were heterogenous nuclei of the growth for zinc crystals. Finer, more uniform and denser zinc crystals were attained by secondary zinc coating with better covering capacity. Zinc coating layer with best morphology was a0proached by secondary zinc coating for 20- 30 seconds.