過氧化氫對AZ31鎂合金硝酸鈰化成皮膜之影響

Effects of Hydrogen Peroxide on the Formation of Cerium Conversion Coatings on AZ31 Magnesium Alloys

本研究探討硝酸鈰溶液中添加過氧化氫對AZ31化成皮膜結構與成長之影響。添加過氧化氫，化成液由澄清透明轉為橙黃色，化成液中三價鈰離子氧化成四價鈰離子，所生成之化成皮膜為二氧化鈰。並且由於氫氣泡破裂所造成的震波，導致皮膜嚴重剝落，且皮膜脫落的程度隨化成溫度上昇而加劇。另外橫截面TEM觀察顯示，皮膜為多層結構，其中與底材相鄰的為多孔的氫氧化鎂，接著為二氧化鈰，其餘的為剝落的二氧化鈰層。

The present study details the effects of hydrogen peroxide in the cerium nitrate solution on the microstructure and growth of the conversion coating on AZ31 magnesium alloys. Adding hydrogen peroxide to the cerium nitrate solution changed its color from clear to orange; meanwhile Cr 3+ was oxidized to Ce 4+. The major overlay of the coating was cerium oxide that had peeled partially from the substrate due to hydrogen evolution at the interface. Increasing solution temperature from 30 to 60℃ resulted in more serious peeling, when the coating, as characterized by cross-sectional TEM, exhibited a multilayer structure. That is, a porous metal hydroxide layer covering intimately on the substrate, followed by a cerium oxide layer, and finally a couple of cerium oxide layers loosely stacking on the surface of the coating.