Mg对Zn--11%Al合金镀层凝固组织及合金层生长的影响

将工业纯铁分别在510℃的Zn-11%Al、Zn-11%Al-1.5%Mg、Zn-11%Al-3%Mg和Zn-11%Al-4.5%Mg合金熔池中进行不同时间的热浸镀,使用X射线衍射仪、扫描电子显微镜、能谱仪等仪器设备,研究Mg含量对Zn-11%Al合金镀层凝固组织和镀层中Fe-Al合金层生长的影响.结果表明：Zn-11%Al合金镀层凝固组织由富Al相和Zn/Al二元共晶组成；随着Zn-11%Al-x%Mg合金中Mg含量的增加,合金镀层的凝固组织中逐渐出现Zn/Al/MgZn2三元共晶、块状 MgZn2相和Al/MgZn2二元共晶.四种合金镀层中合金层主要由Fe2 Al5 Znx和FeAl3 Znx相组成,合金层的厚度随浸镀时间的增加而增加,Mg含量的增加使Fe-Al合金层生长速率指数和生长速率降低.在Zn-11%Al合金镀层中Fe-Al合金层形成的初期,可形成致密稳定的Fe-Al化合物层；热浸镀120 s后,扩散通道的移动使Fe-Al化合物层失稳破裂. Zn-11%Al-x%Mg合金中Mg元素可明显推迟液Zn进入镀层中Fe-Al合金层的时间,使Fe-Al合金层更加稳定和致密.

Effect of Mg on the solidification structure and growth of the intermetallic layer of a Zn--11%Al alloy coating

Zn-11%Al, Zn-11%Al-1. 5%Mg, Zn-11%Al-3%Mg and Zn-11%Al-4. 5%Mg alloy coatings were obtained by dipping pure iron in the alloy bath at 510℃ for different immersion time. The effects of Mg content on the solidification structure of the Zn-11%Al coating and the growth of the Fe-Al intermetallic layer in the alloy coating were investigated by X-ray diffraction, scanning electron microscopy and energy dispersive spectrometry. The results show that the solidification microstructure of the Zn-11%Al alloy coating is composed of Al-rich phase and Zn/Al ternary eutectic. With the increase of Mg content in the Zn-11%Al- x%Mg alloy, Zn/Al/MgZn2 ternary eutectic, blocky MgZn2 phase and Al/MgZn2 binary eutectic occur gradually. The intermetallic layers in the Zn-11%Al alloy coatings with different amounts of Mg consist of Fe2 Al5 Znx phase and FeAl3 Znx phase, and the thickness of the inter-metallic layer increases with the prolongation of immersion time. The increase of Mg content in the hot dip bath reduces the growth-rate index and the growth rate of the intermetallic layer. At the beginning of the hot dip process, a compact and stable Fe--Al alloy layer in the Zn--11%Al alloy coating form on the iron surface. After immersing for 120s, the Fe--Al intermetallic layer is instable and broken because of diffusion path movement. Mg element in the Zn--11%Al--x%Mg alloy can significantly delay the time of liquid zinc into the Fe--Al alloy layer, which makes the Fe--Al alloy layer be more stable and compact.