(1. 國(guó)網(wǎng)湖南省電力有限公司 電力科學(xué)研究院，長(zhǎng)沙 411107 2. 中南大學(xué) 材料科學(xué)與工程學(xué)院，長(zhǎng)沙 410083； 3. 國(guó)網(wǎng)湖南電力有限公司 湘電試驗(yàn)研究院有限公司，長(zhǎng)沙 410004)
摘 要: 采用掃描電鏡和透射電鏡觀察、電阻率和硬度測(cè)試等手段，研究連續(xù)冷卻條件對(duì)7020合金時(shí)效組織性能的影響，并繪制實(shí)驗(yàn)合金的CCT圖。結(jié)果表明：實(shí)驗(yàn)合金的連續(xù)冷卻脫溶產(chǎn)物主要包括GP區(qū)、η′相和η相，高溫階段主要對(duì)應(yīng)η相在彌散粒子、晶界等異質(zhì)形核質(zhì)點(diǎn)上的優(yōu)先析出，中溫階段主要對(duì)應(yīng)η相在基體內(nèi)均勻析出，低溫階段則主要對(duì)應(yīng)GP區(qū)、η′相的析出，實(shí)驗(yàn)合金的臨界冷卻速率達(dá)到700 ℃/min以上。不同冷卻條件引起析出相組態(tài)的變化，導(dǎo)致合金的硬度和電阻率隨冷卻速率降低而發(fā)生相應(yīng)的變化。較慢冷卻速度下的脫溶會(huì)消耗溶質(zhì)原子，從而導(dǎo)致時(shí)效驅(qū)動(dòng)力下降，而合適的冷卻速率下形成的亞穩(wěn)相則可作為時(shí)效強(qiáng)化相的前驅(qū)體，能夠加速時(shí)效強(qiáng)化相析出，導(dǎo)致合金的時(shí)效硬化曲線峰值時(shí)間提前。
關(guān)鍵字: 7020合金；連續(xù)冷卻；顯微組織；CCT圖
（1. Electrical Power Research Institute, State Grid Hunan Electrical Power Company, Changsha 411107, China; 2. School of Materials Science and Engineering, Central South University, Changsha 410083, China; 3. Hunan Xiangdian Test Research Institute Co. Ltd., State Grid Hunan Electrical Power Company, Changsha 410004, China）
Abstract:The effect of continuous cooling process on aging microstructure and properties was investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), electrical resistivity and hardness test. The results show that the continuous cooling precipitations for 7020 alloy are GP zones, η and η′ phases. The high temperature transformation corresponds to the heterogeneous precipitation of η phase. The medium temperature zone corresponds to the homogeneous precipitation of η phase. While, GP zones and η′ phases are precipitated in the low temperature zones. The critical cooling rate for 7020 alloy inhibiting any cooling precipitates is more than 700 ℃/min. The hardness and electrical resistivity change with the extending of cooling ending time with the extending of cooling ending time, since the different microstructures induce by different cooling processes. The precipitation of metastable phases during the cooling process leaded to an earlier peak hardness value is observed. However, extremely slow cooling processes will lead to the significant consumption of alloy atoms, in which the driving force for aging precipitation decreases.
Key words: 7020 alloy; continuous cooling; microstructure; CCT diagram
