AZ91D合金中加入1%La(质量分数)后, 不但形成了条状的Al11La3相和块状的Al8LaMn4相, 而且在粗大α相(Mg17Al12) 周围形成了许多细小的层片状α相, 并使α相进一步网状化. 这些细小的层片状α相明显阻碍了腐蚀的扩展, 提高了AZ91D镁合金的耐蚀性. 条状的Al11La3相和块状的Al8LaMn4相都属于阴极耐蚀相. 其中Al11La3相由于较小的阴极面积, 对加速其周围镁基体的腐蚀不起明显作用; 而块状的Al8LaMn4相阴极面积较大, 与基体构成微电偶腐蚀, 加速了基体的腐蚀.
The microstructure, corrosion morphology and corrosion product of AZ91D and AZ91D-1.0La alloy were investigated. With the addition of 1% La in AZ91D, not only rod-like Al11La3 and blocky Al8LaMn4 phase, but also more fine laminar β phase-Mg17Al12 around large β phase particles formed. The fine laminar β phase obviously restrained the further development of corrosion, which greatly improved the corrosion resistance of AZ91D. Al11La3 phase was cathodic phase, but this phase did not accelerate corrosion of α matrix because Al11La3 was rod-like phases, which only offered a small cathodic area. However, blocky Al10Ce2Mn7 phase obviously accelerated corrosion of α matrix because of its large cathadic area. Al11La3 and Al8LaMn4 are corrosion resistant phases, but they could not restrain the development of corrosion because their distribution was not continuous.
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