铸态Mg-xAl(x=9, 12, 15)合金的组织结构及腐蚀行为研究

Investigation on the microstructure and corrosion behavior of the as-cast Mg-xAl(x=9, 12, 15) alloys

摘要:

通过半连续铸造的方法制备了Mg-xAl(x=9, 12, 15)合金。采用XRD、OM和SEM分析研究了Al含量对铸态Mg-Al合金的组织结构变化的影响。同时,利用浸泡腐蚀实验和动电位电化学极化曲线研究了Mg-xAl(x=9, 12, 15)合金的耐蚀行为。最后,通过SEM观察去除腐蚀产物后样品表面形貌,研究了其腐蚀机理。结果表明：三种合金材料的组织都是由α-Mg相和β-Mg₁₇Al₁₂相组成,而且β相含量随着Al含量的增多而增多。从而研究的三种合金中随β相的增多,合金的耐腐蚀性能逐渐增高,即Mg-15%Al合金的耐腐蚀性能最好,Mg-9%Al的最差。铸态Mg-Al合金在3.5%NaCl溶液中浸泡72小时后,表面都可以形成氧化膜,随着Al含量增高,膜层的稳定性增高。

关键词:铸造Mg-Al合金; 组织结构; 腐蚀行为

Abstract:

The Mg-xAl(x=9, 12, 15) alloys were prepared by meaning of semi-continuous casting. The effects of Al contents on evolution of microstructure of Mg-Al alloy were investigated used X-ray diffraction(XRD), optical microscopy(OM) and scanning electron microscopy(SEM). Meanwhile, the corrosion behaviors of Mg-xAl(x=9, 12, 15) alloys were studied by both hydrogen evolution and Potentiodynamic polarization curves. Moreover, the corrosion mechanism of Mg-xAl(x=9, 12, 15) alloys was also discussed in details based on the SEM corrosion morphologies of as-cast Mg-Al alloys after hydrogen evolution testing for 72 h in 3.5 wt.% NaCl without corrosion products. The results indicated that the microstructure of three alloys is composed of α-Mg phase and β-Mg₁₇Al₁₂ phase. Moreover, the content of beta phase increases with the increase of Al content. As a result, the corrosion resistance of the three alloys was enhanced with the increase of the β phase. The Mg-15%Al alloy has the best corrosion resistance, and Mg-9%Al is the worst. The oxide film formed on the all as cast Mg-Al alloys surface after hydrogen evolution testing for 72 h in 3.5 wt.% NaCl. Furthermore, the stability of the film increased with the increase of Al content.

Key words:As-cast Mg-Al alloy; Microstructure; Corrosion behavior