Abstract
In this work, the use of zinc phosphate coating to protect AZ31 magnesium alloy against corrosion is discussed. In addition, the effect of solution temperature and immersion time as two important process parameters during phosphating on the surface properties and corrosion resistance was studied. The morphology and composition of phosphate films formed on Mg alloy was investigated by using scanning electron microscopy (SEM) and x-ray diffraction (XRD). The results show that the phosphate coatings mainly contain hopeite (Zn3[PO4]2·4H2O) and have flower- and slab-like crystals at lower and higher solution temperatures, respectively. Meantime, electrochemical impedance spectroscopy (EIS) and direct current (DC) polarization were used to assess the corrosion protection property. The EIS results indicate that the phosphate film formed at 60°C during 5 min immersion can greatly improve the corrosion resistance of the AZ31 magnesium alloy.
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