(1. 清華大學(xué) 新材料國際研發(fā)中心，北京100084；
2. 清華大學(xué) 機(jī)械工程系，北京100084；
3. 清華大學(xué) 航天航空學(xué)院，北京100084)
摘 要: 運(yùn)用固體與分子經(jīng)驗(yàn)電子理論(EET)的計(jì)算結(jié)果分別建立Al-Si、Mg-Al兩種合金熔體的剩余化學(xué)鍵的局域價電子結(jié)構(gòu)基本單元即殘余鍵結(jié)構(gòu)模型，從壓力對熔體結(jié)構(gòu)作用的層面，分析熱力學(xué)平衡相圖中最大固溶點(diǎn)和共晶點(diǎn)發(fā)生偏移的本質(zhì)原因，并指出壓力作用下熱力學(xué)平衡相圖的變化是合金熔體微觀結(jié)構(gòu)信息變化的宏觀反映。結(jié)果表明：壓力作用抑制了合金熔體中Si-Si、Al12殘余鍵結(jié)構(gòu)的擴(kuò)散速率，使其不容易“捕捉”到周圍的殘余鍵結(jié)構(gòu)或游動原子，因而形成偏聚的可能性大為減小；而處于“懸空”狀態(tài)的Al鍵會以周圍Mg原子為“橋”將Al12殘余鍵結(jié)構(gòu)連接起來形成包含Mg17Al12結(jié)構(gòu)的原子集團(tuán)，為自發(fā)產(chǎn)生β(Mg17Al12)相凝固核心提供“有效晶胚”，從而使Mg-Mg、Mg-Al原子集團(tuán)內(nèi)Al原子的數(shù)量相對減少。
關(guān)鍵字: Al-Si合金；Mg-Al合金；壓力；殘余鍵結(jié)構(gòu)模型；熔體結(jié)構(gòu)；非平衡相圖
（1. Advanced Materials International R&D Center, Tsinghua University, Beijing 100084, China;
2. Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China;
3. School of Aerospace, Tsinghua University, Beijing 100084, China）
Abstract:By using the calculated results of EET theory, the local valence electron structure elements of residual chemical bonds of Al-Si and Mg-Al alloy melts, that is, the residual bond structure models, were established. From the viewpoint of effect of pressure on melt structure, the essential reason of deviation phenomenon for maximum solution point and eutectic point in thermodynamics equilibrium phase diagram was analysed. Moreover, under pressure condition, the change of thermodynamics equilibrium phase diagram was macroscopic reflection of microstructure change of alloy melt. The results show that the pressure function reduces the diffusion rates of Si-Si and Al12 residual bond structures in alloy melt, making them not easy to capture the other residual bond structures and wandering atoms around them, so the possibility of segregation is decreased greatly. However, taking Mg atoms as “bridge”, the “dangling” Al bonds will connect with Al12 residual bond structures, forming the atomic clusters including Mg17Al12 structures, which supply “effective crystal embryo” for forming β(Mg17Al12) phase spontaneously, and reduce the Al quantity in the Mg-Mg and Mg-Al atom clusters.
Key words: Al-Si alloy; Mg-Al alloy; pressure; residual bond structure model; melt structure; non-equilibrium phase diagram
