( 1. 西南科技大學(xué) 材料科學(xué)與工程學(xué)院， 綿陽 621002;
2. 重慶大學(xué) 材料科學(xué)與工程學(xué)院， 重慶 400044)
摘 要: 通過Gleeble高溫?zé)崮M實(shí)驗(yàn)， 采用加工圖理論分析了AZ31鎂合金在中溫變形過程中的流變失穩(wěn)特征。 結(jié)果表明： AZ31鎂合金在250 ℃進(jìn)行塑性變形時(shí)， 應(yīng)變速率不同將出現(xiàn)不同的變形組織，其規(guī)律與一般金屬的存在顯著差別； 在低應(yīng)變速率（小于0.15 s-1）條件下， 顯微組織出現(xiàn)大晶粒被細(xì)小晶粒包圍的“項(xiàng)鏈”組織特征；當(dāng)變形量足夠大時(shí)， 塑性變形協(xié)調(diào)機(jī)制不能滿足， 出現(xiàn)流變失穩(wěn)， 試樣開裂； 隨著應(yīng)變速率的提高， 由于孿生變形機(jī)制的激活， 大晶粒產(chǎn)生孿生變形， 使晶界處的應(yīng)力集中得到緩解，塑性流變過程逐漸穩(wěn)定。
關(guān)鍵字: 鎂合金； 加工圖； 塑性； 孿生
（ 1. School of Materials Science and Engineering,
Southwest University of Science and Technology, Mianyang 621002，China;
2. School of Materials Science and Engineering,
Chongqing University, Chongqing 400044， China）
Abstract: The instability flow characteristics of AZ31 magnesium alloy at moderate temperature was analyzed by Gleeble simulation test at elevated temperatures. The results show that the microstructures after deformation at 250 ℃ change markedly with the variety of strain rates, which is different from other metal materials. At low strain rates (less than 0.15 s-1), the necklace microstructures, where large grains are encircled with fine grains, scatter over the deformation regions of samples, and then result in cracks in samples with increasing strain because of flow instability. The reason is that the continuity of plastic deformation is breached by necklace microstructures. However, the plastic flow becomes stable gradually, as the strain rate increases, owing to activation of twinning deformation to release the concentration of stress at grains boundaries.
Key words: magnesium alloy; processing map; ductility; twinning
