Phase transformationsin an Cu-35Mn-25Al alloy

• Main Authors: Chu, Kuo Lin, 朱郭麟
• Other Authors: Liu Tzeng-Feng
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/72793166954131702577

碩士 === 國立交通大學 === 材料科學與工程研究所 === 85 === Phase transformations in the Cu-35Mn-25Al alloy have been investigated by using transmission electron microscope (TEM) and energy-dispersive X-ray spectrometer (EDS). In the as-quenched condition, the microstructure of the alloy was a mixture of ( L21+B2+L-J ) phases. The B2 phase with a fine particle shape was present within L21 domains. This feature has never been observed by other workers.The L-J phase is a new phase having an orthorhombic structure, which was found firstly by T. F. Liu and S. C. Jeng in a Cu2.2Mn0.8Al alloy.[2]When the alloy was aged at 300℃, the fine B2 particles grew and no evidence of the L-J phase could be detected. Therefore , the microstructure of the alloy at 300℃is a mixture of ( L21+B2 ) phases. When the alloy was aged at 500℃for short times, the shape of the B2 particles changed from particle into needle-like. The microstructure is still ( L21+B2 ) phases. However, when the aging time wasincreased at this temperature, two kinds of precipitates, namely γ- brass andβ- Mn, started to appear on the grain boundary. After prolonged aging at thistemperature, the grain boundary precipitation of(γ- brass + β- Mn) became predominant . Therefore, the stable microstructure of the alloy at 500℃is (γ- brass + β- Mn).The coexistence of the γ- brass and β- Mn precipitates has never been observed by other workers in the Cu- Mn-Al alloys. A further increase in the aging temperature up to 650℃ resulted in a rapid growth of theβ- Mn precipitates within L21 matrix and no γ- brass precipitates could be observed. Progressively higher temperature aging and quenching experiments indicated that when the alloy was aged at 680℃or above, the microstructure of the alloy was the same as that in the as-quenched condition.