(1. 中南大學(xué) 材料科學(xué)與工程學(xué)院，長(zhǎng)沙 410083；
2. 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)
摘 要: 對(duì)7A04鋁合金固溶處理后的連續(xù)冷卻轉(zhuǎn)變(CCT圖)進(jìn)行測(cè)定。通過(guò)動(dòng)態(tài)電阻法測(cè)得冷卻過(guò)程的電阻—溫度曲線，根據(jù)曲線斜率的變化規(guī)律確定相變開(kāi)始點(diǎn)、結(jié)束點(diǎn)以及臨界冷卻速度所處范圍，繪制該合金的CCT圖，利用掃描電鏡和X射線衍射分析觀察連續(xù)冷卻過(guò)程中合金的組織轉(zhuǎn)變。結(jié)果表明：電阻對(duì)連續(xù)冷卻過(guò)程的組織變化敏感，動(dòng)態(tài)電阻法測(cè)得的CCT圖是可信的；經(jīng)470℃、1 h固溶處理后，抑制相變發(fā)生的臨界冷卻速度低于35.37 ℃/s，但高于9.96 ℃/s；隨著冷卻速度的增加，相變開(kāi)始溫度和結(jié)束溫度均降低，相變主要集中在150~400 ℃的溫度區(qū)間發(fā)生；快速冷卻時(shí)，合金保持較高的過(guò)飽和度，在60 ℃以下仍有相變發(fā)生，慢速冷卻時(shí)，MgZn2平衡相在晶內(nèi)和晶界大量析出并逐漸長(zhǎng)大和粗化。
關(guān)鍵字: 7A04鋁合金；CCT圖；動(dòng)態(tài)電阻；相變
of 7A04 aluminum alloy
（1. School of Materials Science and Engineering, Central South University, Changsha 410083, China;
2. Key Laboratory of Nonferrous Metals Materials Science and Engineering, Ministry of Education,
Central South University, Changsha 410083, China）
Abstract:The continuous cooling transformation (CCT) curves of aluminum alloy 7A04 were measured. The electrical resistance—temperature curves during the continuous cooling processes were obtained by in-situ resistance measurement. The starting and finishing temperatures of the phase transformation and critical cooling rate range were established by analyzing the slope change of the obtained curves, and then CCT curves were drawn. The microstructure evolution of the alloy during cooling process was observed by SEM and XRD. The results show that the electrical resistivity of the sample is sensitive to the microstructure change produced by continuous cooling transformation, and the CCT curves obtained by in-situ resistance measurement are credible. After solution treated at 470 ℃ for 1 h the critical cooling rate to prevent the phase transformation of the samples is above 9.96 ℃/s but below 35.37 ℃/s, the phase transformation starting and finishing temperatures decrease with increasing cooling rates and it mainly happens in the temperature range of 150−400 ℃. High speed cooling leads to high concentration of solute thus the phase reaction happens even below 60 ℃, and low speed cooling brings precipitation, growth and coarsening of MgZn2 equilibrium phase in the grains and at the grain boundaries.
Key words: 7A04 aluminum alloy; continuous cooling transformation curves; in-situ electrical resistance; phase transformation
