銅-24.8錳-30.0鋁合金相變化

Abstract

我們利用 STEM, EDS 對銅-24.8錳-30.0鋁合金相變化作一系列觀 察,發現其淬火狀態下的顯微結構呈現出 (B2+L21+L-J) 相的混合。 而在 淬火狀態下, B2相的存在從未被其他學者在銅-錳-鋁合金系統中發現過。 在此值得一提的是,L-J 相為劉增豐博士及鄭祥誠博士首度在 Cu2.2Mn0.8 Al合金中發現的新相,具有 orthorhombic 結構。 當我們對此合金 在 250℃至 700℃溫度範圍內施以不同時間的時效處理後發現, γ-brass 會在基地間析出, 與基地間呈 cubic-cubic 的方向關係;同時並發現到 L21 相 的量會隨著 γ-brass 析出量的增加而減少。當時效溫度範圍在 350℃ 至 450℃ 之間時,γ-brass 會以 cuboid 型狀在基地間均勻析出; 而時效溫度範圍提高至 500℃至 700℃時,γ-brass 則以塊狀析出。 We made a series of the STEM and EDS investigations on the phase transformations of the Cu-24.8Mn-30.0Al alloy. It was found that the as-quenched microstructure of the alloy was a mixture of (B2+L21+L-J) phases[1]. The existence of the B2 phase under the as-quenched condition has never been found by other workers in the Cu-Mn-Al alloy system. It is worthy to note that the L-J phase having an orthorhombic structure is a new phase which was found firstly by T.F. Liu and S.C.Jeng in a Cu2.2Mn0.8 Al alloy[2]. As the aging processes were performed at temperatures ranging from 250℃ to 700℃, the γ-brass precipitates were observed to occur within the matrix, and the orientation relationship between the γ-brass precipitate and the matrix is cubic to cubic. Along with the increase of the γ- brass precipitates, the quantity of the L21 phase decreased. The γ-brass precipitates have a cuboid shape as the aging temperatures were in the range of 350℃-450℃, while the γ- brass precipitates changed into a grainual shape as the aging temperatures raised to the range from 500℃ to 700℃.