硅含量和浸镀温度对Zn-6%Al-3%Mg镀层表面层组织的影响

Influence of Si content and immersing temperature on surface structure of Zn-6%Al-3% Mg alloy coating

将纯铁片在不同硅含量和不同温度的Zn-6%Al-3%Mg(ZAM,质量分数)合金熔池中浸镀60 s,制备各种热浸镀ZAM合金镀层。采用DTA测试不同硅含量ZAM镀锌合金的开始凝固温度,利用扫描电镜、能谱仪和X线衍射仪等仪器观察分析各种合金镀层的表面组织。研究结果表明:硅元素的加入使镀层表面组织中粗大树枝状富Al相发生明显的细化,且硅含量越高树枝晶越细小;随着硅含量的增加,树枝状富Al相的体积分数下降,Zn/Al/Mg Zn2三元共晶组织体积分数增加;硅的加入使η-Zn相和Mg Zn2相在镀层表面组织中消失,同时镀层表面组织中出现了Mg_2Si颗粒。纯铁片在Zn-6%Al-3%Mg-0.1%Si熔池中浸镀60 s时,随着浸镀温度升高,镀层表面中的树枝状富Al相明显粗化,且其体积分数明显减少,在530℃浸镀后镀层中出现异常表层组织。

The ZAM alloy coatings were obtained by dipping pure iron specimens in Zn-6%Al-3%Mg（ZAM, mass fraction） baths with different Si contents at different temperatures for 60 s. The freezing points of ZAM alloys with different Si contents were analyzed by DTA test. The surface structure of various alloy coating was investigated by using scanning electron microscope coupled with energy dispersive spectroscopy and X-ray diffractometry. The results show that thick dendritic Al-rich phase in the surface structure is refined obviously by adding small amount of Si, and the dendrites become finer with the increase of Si content. The volume fraction of dendritic Al-rich phase falls and that of Zn/Al/Mg Zn2 ternary eutectic structure rises with the increase of Si content. η-Zn and Mg Zn2 phases disappear, while Mg2 Si particles grow in the surface structure because of the addition of Si. When dipping pure iron specimens in Zn-6%Al-3%Mg-0.1Si bath for 60 s, dendritic Al-rich phase in the surface structure becomes coarsening obviously and the volume fraction decreases with the increase of dipping temperature. Abnormal surface structure occurs when the dipping temperature is 530 ℃.