熱浸鍍鋁鐵鋁錳碳合金之研究

Abstract

鐵鋁錳碳合金經由熱浸鍍鋁處理後，其鍍層主要是由鋁層及介金屬層所構成。在本研究中，我們利用穿透式電子顯微鏡清楚地看到介金屬層的形態(morphology)是一種具有柱狀晶的細微多晶結構，其晶粒直徑大小平均只有200~220 nm，並且明確地鑑定出介金屬層為具有正交晶結構(orthorhombic structure)的(Fe,Mn)2Al5介金屬相，其晶格常數為a = 0.752 nm, b = 0.667 nm及c = 0.417 nm。另外，我們也清楚地看到在緊鄰基材的界面(interface)處，除了(Fe,Mn)2Al5介金屬相外，並沒有發現其它相的存在。當鐵鋁錳碳合金在進行熱浸鍍鋁過程中，鍍層中(Fe,Mn)2Al5介金屬層之成長為一種經由擴散所控制(diffusion-controlled)的成長機構。由於鐵鋁錳碳合金基材中合金成份的影響，使得(Fe,Mn)2Al5介金屬具有相當小的成長活化能13.9 KJ/mole，遠小於在一般碳鋼中Fe2Al5的155 KJ/mole。 在熱浸鍍鋁鍍層特性方面，藉由電化學極化曲線測試發現，經熱浸鍍鋁處理後的鐵鋁錳碳合金在5 % 氯化鈉水溶液中的腐蝕電流遠小於具有極佳抗腐蝕能力的304不鏽鋼。鹽霧試驗也實際地證實這項結果。另外，我們也發現，由於熱浸鍍鋁之鐵鋁錳碳合金在900℃高溫的大氣氣氛氧化過程中，在其表面會形成具有保護效果的α-Al2O3氧化層，因此不但顯著地提升其抗氧化能力，而且較316耐熱不鏽鋼來得更優異。

The aluminum layer and the intermetallic compound coating layer formed by hot dip aluminizing of Fe-Al-Mn-C alloy have been investigated. The morphology of the intermetallic compound had fine polycrystalline structure with columnar grains. The average grain size of the intermetallic compound was about 200 ~ 220 nm. Transmission electron microscopy examinations indicated that the intermetallic compound formed on the diffusion coating layer of the hot dip aluminum coated Fe-Al-Mn-C alloys was (Fe,Mn)2Al5. The (Fe,Mn)2Al5 has an orthorhombic structure with lattice parameters a = 0.752 nm, b = 0.667 nm and c = 0.417 nm. The (Fe,Mn)2Al5 could only be observed on the interface between the intermetallic compound layer and the substrate. The growth of the intermetallic layers was dominated by diffusion- controlled kinetics. The activation energy for the growth of the (Fe,Mn)2Al5 intermetallic phase was about 13.9 KJ mol-1, which was much lesser than that of the Fe2Al5 formed by hot dip aluminizing in carbon steel(Q = 155 KJ mol-1). By analyzing electrochemical polarization curves, it was found that the hot dip aluminum coated Fe-Al-Mn-C alloy could decrease the corrosion current density (Icorr) in 5 % NaCl solution, and the corrosion current density (Icorr) was much lesser than that of the commercial 304 stainless steel. Furthermore, the salt-spray test revealed that the corrosion resistance of the hot dip aluminum coated Fe-Al-Mn-C alloys was better than that of the commercial 304 stainless steel. Owing to the formation of theα-Al2O3, the high temperature oxidation resistance behavior of the hot dip aluminum coated Fe-Al-Mn-C alloy was superior to that of the commercial 316 stainless steel.