退火熱處理對熱浸鍍鋁鐵鋁錳碳合金鍍層的影響之研究

Abstract

本篇論文主要研究700℃和800℃退火熱處理對熱浸鍍鋁之鐵鋁錳碳合金鍍層中介金屬相的影響，並利用掃描穿透式電子顯微鏡觀察介金屬層的多晶組織結構，結果發現晶粒直徑大小從原本熱浸鍍鋁後的200~220 nm，在經過700℃和800℃退火熱處理30分鐘後，分別成長至600~800 nm及1200~1600 nm。介金屬層在退火熱處理過程中的成長亦被證實是一種由擴散所控制的成長機構。 熱浸鍍鋁鐵鋁錳碳合金在經700℃退火熱處理30分鐘後，介金屬層為具有正交晶結構(orthorhombic structure)的(Fe,Mn)2Al5單一介金屬相，然而，在800℃退火熱處理30分鐘後，會有一種A12 α-Mn在(Fe,Mn)2Al5介金屬相中析出，其中A12 α-Mn僅含有約24.4at.%的錳，明顯地比目前已在Al-Mn, Fe-Mn或Fe-Al-Mn-Cr合金中所發現的A12 α-Mn還要來得低許多，同時其存在的溫度卻高甚多。另外，800℃退火熱處理後，雖然在靠近鋁層的外層介金屬相與靠近基材的內層介金屬同樣為(Fe,Mn)2Al5相，但是隨著成份的擴散變化，從外層到內層(Fe,Mn)2Al5介金屬相的晶格常數會有變小的趨勢。 有關介金屬層的機械性質方面，我們發現在經過700℃和800℃退火熱處理30分鐘後，介金屬層硬度明顯地下降，因此在對其施加25gw荷重連續10秒條件下，並未在壓痕附近觀察到原本在未退火熱處理前所發現的微裂縫。

The effects of annealing treatments at 700℃ and 800℃ on the internetallic phases formed in the coating layer of the hot dip aluminized Fe-Al-Mn-C alloys have been investigated. Scanning transmission electron microscopy observations revealed that after hot dip aluminum coated Fe-Al-Mn-C alloys, the average grain size of the intermetallic phase was 200~220 nm, and then grew to about 600~800 nm and 1200~1600 nm after annealing treatments at 700℃ and 800℃ for 30 minutes. Experimental results showed that the growth of the intermetallic layers was dominated by diffusion-controlled kinetics during annealing treatment. After annealing treatment at 700℃ for 30 minutes, the intermetallic phase formed in the coating layer of the hot dip aluminized Fe-Al-Mn-C alloys was the single intermetallic phase (Fe,Mn)2Al5 with orthorhombic structure. In contrast to this observation, the A12 α-Mn would precipitate at the grain boundary of the intermetallic phase (Fe,Mn)2Al5 after annealing treatments at 800℃ for 30 minutes. EDS analyses indicated that the A12 α-Mn only contain about 24.4at.% manganese. Compared to Al-Mn, Fe-Mn, Fe-Al-Mn and Fe-Al-Mn-Cr alloys, it was found that the A12 α-Mn observed in the present alloy consisted of lower manganese and had a higher existing temperature. In addition, the lattice constant of the intermetallic phase (Fe,Mn)2Al5 from outer layer to inner layer would decrease with composition change caused by the diffusion process. Also, microhardness test revealed that the hardness of the intermetallic layer obviously decreased after annealing treatments at 700℃ and 800℃.