Effect of Ca on Corrosion Resistance Behavior of as-Cast AZ91 Magnesium Alloys

摘要:

研究了0.5，1.0和1.5（质量分数，%，下同）的Ca对铸态AZ91镁合金微观组织和耐蚀性的影响。利用OM、SEM/EDS和XRD观察金相组织、进行微观分析和确定相组成。分别采用静态失重腐蚀、电化学腐蚀和盐雾腐蚀对不同成分的AZ91合金进行实验。结果表明，0.5Ca的存在没有形成任何新的金属间相，而是通过溶解于第二相和基质中抑制β-Mg17Al12相的不连续沉淀。AZ91-1.0Ca合金耐蚀性最好。AZ91-1.0Ca和AZ91-1.5Ca合金中出现了骨状的Al4Ca相，并且β相尺寸显著下降。在AZ91-1.0Ca合金中，β相分布十分均匀。因此，可以认为，随着不同含量Ca的加入，铸态AZ91镁合金耐蚀性的变化是由于其微观组织的变化而引起的。

Abstract:

The effects of Ca on the microstructures and the corrosion resistance of as-cast AZ91 alloys with contents of 0.5 wt%, 1.0 wt% and 1.5 wt% Ca were investigated. Constant immersion technique, potentiodynamic polarization and salt spray test were employed to determine the corrosion resistance of AZ91 alloys. Morphological characterization by optical microscope (OM), microanalysis by scanning electron microscopy (SEM)/energy dispersed spectroscopy (EDS) and phase identification by X-ray diffractometry (XRD) indicate that the presence of 0.5 wt% Ca does not form any new intermetallic phase but restrains the discontinuous precipitation of the β-Mg17Al12 phase through dissolution in both the second phase and magnesium matrix. The AZ91 alloy with the addition of 1.0 wt% Ca exhibits the optimal corrosion resistance. Al4Ca phase in bone-like morphology appears in the alloys with a larger quantity of Ca (1.0 wt% and 1.5 wt%), in line with a marked size reduction of the β-Mg17Al12 phase. The β-Mg17Al12 phase is distributed uniformly among the matrix of the AZ91-1.0Ca alloy. The variation of the corrosion resistance of the as-cast AZ91 alloys with the addition of Ca is attributed to the change of the microstructure.