Zn-Al-Mg合金的凝固组织及其耐腐蚀性能

Microstructure and Corrosion Resistance of Solidified Zn-Al-Mg Alloys

在电阻炉中熔炼得到Zn-Al-Mg合金,然后分别在水冷、空冷和炉冷的条件下冷却到室温。采用SEM观察不同凝固方式下的Zn-Al-Mg合金微观组织,并采用电化学方法研究了凝固方式对样品耐腐蚀性能的影响。结果表明,Zn-Al-Mg合金的微观组织由富Zn的初晶组织以及Zn-Al-Mg共晶组织构成。采用炉冷方式得到的Zn-Al-Mg合金中的初晶组织尺寸最大,比例最高。随着合金凝固速度的提高,合金中的初晶组织显著细化,共晶组织所占比例增大,共晶组织从颗粒状转变为层片状。采用不同凝固方式得到的Zn-Al-Mg合金的自腐蚀电位相近,但是自腐蚀电流以及电化学阻抗谱有明显差异,炉冷方式的Zn-Al-Mg合金的自腐蚀电流最小,耐腐蚀性能最好。

Due to high protection performance for cut edges, much attention was focused on Zn-Al- Mg coating. Considering hot-dip galvanizing technology was widely applied for the Zn-Al-Mg coating, so- lidification should strongly influence its microstructure and corrosion properties. In this work, a Zn-Al-Mg alloy was melted in a resistance furnace and then cooled to room temperature with different solidification processes, including water quench, air cooling and furnace cooling. Scanning electron microscopy （SEM） was applied to analyzed the microstructure of the alloys solidified with different processes. Moreover, the effect of solidification on corrosion resistance was studied by electrochemical method. Results show that microstructure of the Zn-Al-Mg alloy consists of Zn-dch primary grains and eutectic of Zn, AI and Mg. It could be found that among others, the furnace cooled Zn-Al-Mg alloy presents the largest size and ratio of the primary grains. With the increasing solidification rate, the primary grains turn to be finer and more eutectic appears, besides, the eutectic transforms from granular-like to lamellar-like. Electrochemical test indicates that the corrosion potentials for all the alloys solidified with different ways are more or less the same level but their corrosion currents and plots of electrochemical impedance spectroscopy （EIS） are re- markable different. The corrosion current of the furnace cooled alloy is the smallest, which means the highest corrosion resistance.