添加鎂離子對於鍍鋅鋼板磷酸鹽化成皮膜的影響

The Effect of Magnesium Ions in Phosphate Coatings on Hot-dip Galvanized Steels

六價鉻鈍化處理常用來提升熱浸鍍鋅鋼板（Hot-dip galvanized steel, GI）的抗蝕性，然而，六價鉻具有致癌性，同時嚴重污染生態環境，已嚴格限用，因此，開發無鉻鈍化處理之製程更形迫切。本研究探討添加鎂離子對於GI鋼板磷酸鹽皮膜微結構與性質之影響，以掃描式電子顯微鏡（SEM）、穿透式電子顯微鏡（TEM）、能量散佈光譜儀（EDS）及X光繞射儀（XRD）分析皮膜微結構、化學組成及其結晶構造，並藉由極化曲線及鹽霧試驗評估皮膜的抗蝕性。研究結果顯示，於磷酸鹽處理液中，添加適當含量的鎂離子，可有效減小磷酸鹽皮膜之晶粒大小及提升皮膜之覆蓋率，並進而提升鋼板之抗蝕性。

Hexavalent chromium based conversion coatings have been widely used to improve the corrosion resistance of hot-dip galvanized (GI) steels. However, hexavalent chromium is toxic and unfriendly to the environment. Therefore, a process of applying alternative chromium-free conversion coatings on GI steels is urgently and much needed. This study investigated the effect of Mg2+ on the microstructure and property of a phosphate coating on a GI steel. The morphology, chemical composition and crystalline structure of the coating were analyzed using SEM, TEM, EDS.and XRD. The corrosion resistance of the coating was evaluated by polarization analyses and salt spray tests. The results showed that adding a proper amount of magnesium ions to a phosphate solution could reduce the grain size of the phosphate coating and increase the coverage of the coating, which could in turn promote the corrosion resistance of the treated GI steel.