Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/43489
標題: Applications of carbonic acid solution for developing conversion coatings on Mg alloy
作者: Yu, B.L.
汪俊延
Lin, J.K.
Uan, J.Y.
關鍵字: Mg alloy
AZ91D alloy
corrosion
conversion coating
carbonic acid
az91d magnesium alloy
corrosion-resistance
formation mechanism
zn
alloy
film
protection
performance
stannate
cerium
layer
期刊/報告no:: Transactions of Nonferrous Metals Society of China, Volume 20, Issue 7, Page(s) 1331-1339.
摘要: Works on exploring an environmentally clean method for producing an Mg,Al-hydrotalcite (Mg(6)Al(2)(OH)(16)CO(3)center dot 4H(2)O) layer and/or calcium carbonate (CaCO(3)) layer on Mg alloy in a carbonic acid solution system (aqueous HCO(3)(-)/CO(3)(2-) or Ca(2+)/HCO(3)(-)) at 50 degrees C were reviewed. Conversion treatment for the Mg,Al-hydrotalcite conversion coating was as follows. Mg alloy was treated first in acidic HCO(3)(-)/CO(3)(2-) aqueous for precursor layer formation on Mg alloy surface and then in alkaline HCO(3)(-)/CO(3)(2-) aqueous to form a crystallized Mg,Al-hydrotalcitc 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 CaCO(3) coating on Mg alloy, the aqueous Ca(2+)/HCO(3)(-) with a saturated Ca(2+) content was employed for developing a CaCO(3) coating on Mg alloy. A dense CaCO(3) coating could yield on Mg alloy surface in 2 h. Corrosion rate (corrosion current density, J(corr)) of the Mg,Al-hydrotalcite-coated sample and CaCO(3)-coated AZ91D sample was 7-10 mu A/cm(2), roughly two orders less than the J(corr) of the as-diecast sample (about 200 mu A/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.
URI: http://hdl.handle.net/11455/43489
ISSN: 1003-6326
文章連結: http://dx.doi.org/10.1016/s1003-6326(09)60300-9
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