超声振动场对热浸镀稀土铝表面层厚度影响的动力学分析

Dynamics Analysis of Surface Layer Thickness Growth of Hot Dip RE-Al Coating under Ultrasonic Vibration Field

用溶剂法制备了稀土铝镀层,采用金相显微镜、扫描电镜观察测定了超声场对热浸镀稀土铝表面层厚度的影响,绘制了表面层厚度变化的动力学曲线。研究得知,稀土铝镀层由表面层和过渡层组成。通过厚度测定发现,过渡层厚度遵循抛物线生长规律,而表面层的厚度变化则明显不同。随着热浸稀土铝时间的延长,表面层厚度经历了先减少至谷值,然后增加到峰值,又减少至稳定值的3个阶段。每一阶段控制厚度变化的因素不同,将其变化过程分为由凝固 重熔控制的第Ⅰ阶段,由浸润 凝固控制的第Ⅱ阶段和完全由浸润控制的第Ⅲ阶段。不管是否施加超声场,表面层厚度变化的规律相似,只不过施加超声场后表面层厚度有不同程度的减小,同时表面层的组织变得更加均匀。

The hot dip REAl coating on A3 steel was carried out by promotion flux method. The influence of ultrasonic field on the growth of surface layer of HDA REAl coating has been studied by MOM and SEM, and the growth of surface layer with time has been drafted. The results show that the REAl coating on A3 steel is composed of surface layer and transition layer. It has been found that the thickness of transition layer changes with time according to a parabola rule while the change of surface layer thickness dose not. There exist three stages in the growth of surface layer with hot dip time. First, the thickness of surface layer declines to a valley point, then increases to a peak value as second stage, and then declines again to a nearly constant value in third stage. The controlling factors of the thickness change with time are different at three stages. In first stage (Ⅰ) the controlling factor is solidificationremelting of Al on AlFe interface, and in second stage (Ⅱ) it is soakingsolidification, while in third stage is soaking of melted Al into specimen surface. Under the same hot dip conditions, the regularity of thickness growth of surface layer in ultrasonic field is similar to that without ultrasonic field, but the thickness of surface layer is thinner and the surface microstructure becomes more uniform.