Works on exploring an environmentally clean method for producing an Mg,Al-hydrotalcite(Mg6Al2(OH) 16CO3·4H2O) layer and/or calcium carbonate(CaCO3) layer on Mg alloy in a carbonic acid solution system(aqueous HCO3-/CO3 2-or Ca 2+ /HCO3-) at 50℃ were reviewed.Conversion treatment for the Mg,Al-hydrotalcite conversion coating was as follows.Mg alloy was treated first in acidic HCO3-/CO3 2-aqueous for precursor layer formation on Mg alloy surface and then in alkaline HCO3-/CO3 2-aqueous to form a crystallized Mg,Al-hydrotalcite coating.Duration of an Mg,Al-hydrotalcite coating on Mg alloy surface was reduced from 12 h to 4 h by the conversion treatment.On the other hand,for reducing the formation time of CaCO3 coating on Mg alloy,the aqueous Ca 2+ /HCO3-with a saturated Ca 2+ content was employed for developing a CaCO3 coating on Mg alloy.A dense CaCO3 coating could yield on Mg alloy surface in 2 h.Corrosion rate(corrosion current density,Jcorr) of the Mg,Al-hydrotalcite-coated sample and CaCO3-coated AZ91D sample was 7-10μA/cm 2,roughly two orders less than the Jcorr of the as-diecast sample(about 200μA/cm 2) . No corrosion spot on the Mg,Al-hydrotalcite-coated sample and CaCO3-coated sample was observed after 72 h and 192 h salt spray test,respectively. Works on exploring an environmentally friendly method for producing an Mg, Al-hydrotalcite (Mg6Al2 (OH) 16CO3.4H2O) layer and / or calcium carbonate (CaCO3) layer on Mg alloy in a carbonic acid solution system (aqueous HCO3- / CO3 2 -or Ca 2+ / HCO 3 -) at 50 ° C were reviewed. Conversion treatment for the Mg, Al-hydrotalcite conversion coating was as follows. Mg alloy was treated first in acidic HCO3- / CO 3 2-aqueous for precursor layer formation on Mg alloy surface and then in alkaline HCO3- / CO3 2-aqueous to form a crystallized Mg, Al-hydrotalcite coating. Duration of an Mg, Al-hydrotalcite coating on Mg alloy surface reduced from 12 h to 4 h by the conversion treatment. On the other hand, for reducing the formation time of CaCO3 coating on Mg alloy, the aqueous Ca2 + / HCO3-with a saturated Ca2 + content was employed for developing a CaCO3 coating on Mg alloy. A dense CaCO3 coating could yield on Mg alloy surface in 2 h. Corrosion rate (corrosion current density, Jcorr) of the Mg, Al-hydrotalcite-coated sample and about 2 orders less than the Jcorr of the as-diecast sample (about 200 μA / cm 2). No corrosion spot on the Mg, Al-hydrotalcite-coated sample and CaCO 3 -coated sample was observed after 72 h and 192 h salt spray test, respectively.