(1. 中南大學 材料科學與工程學院，長沙 410083；
2. 中南大學 有色金屬材料科學與工程教育部重點實驗室，長沙 410083；
3. 包頭職業(yè)技術學院，包頭 014030；
4. 中南大學 輕質(zhì)高強結(jié)構材料國家重點實驗室，長沙 410083；
5. 河南省緊固連接技術重點實驗室，信陽 464000)
摘 要: 采用Kahn撕裂實驗，結(jié)合金相、掃描電鏡、掃描透射電鏡、數(shù)字圖像相關法和電子背散射衍射等手段，研究了Cu含量對Al-9.0Zn-1.5Mg-xCu合金斷裂韌性的影響規(guī)律。結(jié)果表明：隨著Cu含量從0%增大到2.6%(質(zhì)量分數(shù))，合金斷裂韌性先逐漸增大，在Cu含量為1.0%~1.3%時達到最高值，而后大幅減小。隨著Cu含量從0%增大到1.0%~1.3%，合金的再結(jié)晶晶粒面積分數(shù)逐漸增大，導致裂紋形核過程的變形量和穿過再結(jié)晶晶粒擴展的比例增大；裂紋單位面積形核功(UIE)和單位面積擴展功(UPE)逐漸增大。Cu含量為2.6%時，合金殘余第二相的面積分數(shù)、晶界上部分η相的尺寸增大，導致裂紋形核過程的變形量減小；η′強化相的間距減小，導致晶內(nèi)-晶界強度差和裂紋沿再結(jié)晶晶界擴展的比例明顯增大；UIE和UPE均大幅減小。
關鍵字: Al-Zn-Mg-Cu合金；Cu含量；斷裂韌性；裂紋形核功；裂紋擴展功
（1. School of Materials Science and Engineering, Central South University, Changsha 410083, China;
2. Key Laboratory of Non-ferrous Metals Materials Science and Engineering, Ministry of Education, Central South University, Changsha 410083, China;
3. Baotou Vocational & Technical College, Baotou 014030, China;
4. National Key Laboratory of Light and High Strength Structural Materials, Central South University, Changsha 410083, China;
5. Henan Key Laboratory of Fastening Connection Technology, Xinyang 464000, China）
Abstract:The effect of Cu content on the fracture toughness of Al-9.0Zn-1.5Mg-xCu alloys was investigated by means of Kahn-tear test, optical microscopy (OM), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), digital image correlation (DIC), and electron backscattered diffractionometry (EBSD). With the increase of Cu content from 0% to 2.6% (mass fraction), the fracture toughness of alloys first increases, reaching the maximum value at 1.0%-1.3%, and then decreases greatly. With the increase of Cu content from 0% to 1.0%-1.3%, the area fraction of recrystallized grains increases gradually, leading to an increase in the deformation amount during crack initiation and the proportion of transgranular fracture; therefore, unit initiation energy (UIE) and unit propagation energy (UPE) increase gradually. When Cu content is 2.6%, the area fraction of residual phase increases and there are some large η phase particles at grain boundaries, leading to a decrease in deformation amount during crack initiation; the spacing of η′ strengthening precipitates decreases, leading to an increase in the strength difference between the grain interior and the grain boundary and therefore higher proportion of intergranular fracture. As a result, UIE and UPE decrease greatly.
Key words: Al-Zn-Mg-Cu alloy; Cu content; fracture toughness; unit initiation energy; unit propagation energy
