(1. 中南大學(xué) 有色金屬材料科學(xué)與工程教育部重點(diǎn)實(shí)驗(yàn)室，長(zhǎng)沙 410083；
2. 中南大學(xué) 航空航天學(xué)院，長(zhǎng)沙 410083)
摘 要: 采用原位電阻法測(cè)得以不同速率連續(xù)冷卻2A12鋁合金的電阻率—溫度曲線(xiàn)，根據(jù)曲線(xiàn)斜率變化確定相變點(diǎn)及臨界冷卻速率，利用透射電鏡觀察連續(xù)冷卻過(guò)程特征溫度點(diǎn)的淬火組織，繪制出實(shí)驗(yàn)合金的連續(xù)冷卻轉(zhuǎn)變曲線(xiàn)(CCT圖)。結(jié)果表明：2A12合金連續(xù)冷卻相變主要集中在220~400 ℃的溫度區(qū)間，隨著冷卻速率的增加，相變結(jié)束溫度一直呈下降的趨勢(shì)，但相變開(kāi)始溫度在達(dá)到某冷卻速率時(shí)驟升，然后繼續(xù)降低，抑制相變的臨界冷卻速率稍大于38 ℃/s。慢速連續(xù)冷卻實(shí)驗(yàn)合金時(shí)，固溶度減小是引起電阻率變化的主要原因，固溶體脫溶的動(dòng)力學(xué)行為與等溫相變規(guī)律相似，可較好地用Johnson−Mehl−Avrami (JMA)方程描述。
關(guān)鍵字: 2A12鋁合金；原位電阻；相變；連續(xù)冷卻轉(zhuǎn)變
studied by using in-situ electrical resistivity measurement
（1. Educational Key Laboratory of Non-ferrous Metal Material Science and Engineering,
Central South University, Changsha 410083, China;
2. School of Aeronautics and Astronautics, Central South University, Changsha 410083, China）
Abstract:The electric resistivity versus temperature curves of 2A12 aluminum alloy were recorded during continuous cooling using the in-situ electrical resistivity measurement. The phase transformation temperatures and critical cooling rate without phase transition of the alloy can be obtained from the relationships of electrical resistivity vs temperature curves. TEM was applied to the microstructure observation during the continuous cooling process. CCT diagrams of the tested samples can be established. The results show that the phase transformations of the tested alloy mainly take place between 220 ℃ and 400 ℃. The phase transformation finishing temperature decreases with the increase of cooling rates. While the phase transformation starting temperature increases suddenly until the cooling rate reaches some value, then decreases with the increase of cooling rates. The critical cooling rate for preventing phase transformation is above 38 ℃/s. The decrease of solid solubility is the main reason for variation of electric resistivity with a low cooling rate of the alloy. The decomposition of solid solution of the alloy is similar with the isothermal phase transformation, which can be well described by the Johnson−Mehl−Avrami (JMA) equation.
Key words: 2A12 aluminum alloy; in-situ electric resistivity; phase transformation; continuous cooling
