本文關(guān)鍵詞：鎂鋁合金凝固特性與固液界面結(jié)構(gòu)的分子動力學研究　出處：《南昌大學》2016年碩士論文　論文類型：學位論文

  更多相關(guān)文章： 分子動力學方法 凝固特性 固液界面結(jié)構(gòu) 異質(zhì)形核

【摘要】：鎂合金作為21世紀極具潛力和應用價值的綠色工程材料,具有好的切削加工性能、比強度高以及抗沖擊、阻尼性能好等眾多優(yōu)點,在航空航天材料、軍事、醫(yī)藥化工、金屬壓鑄件和汽車工業(yè)等領(lǐng)域得到了廣泛的應用。但是由于鎂合金的塑性和成形性能較差,限制了其應用和發(fā)展。同時隨著科學技術(shù)領(lǐng)域的不斷創(chuàng)新與進步,對材料性能的要求越來越高,以實驗手段為主的材料研究方法存在許多局限性,已經(jīng)難以滿足現(xiàn)階段對材料研發(fā)的要求,所以通過計算機模擬新技術(shù)來深入探索新材料的優(yōu)良性能成為一種趨勢。分子動力學模擬技術(shù)可以觀察金屬熔體在高速凝固過程中原子的微觀結(jié)構(gòu)變化,在對材料宏觀性質(zhì)的計算上也具有很高的準確度,逐漸成為材料研究領(lǐng)域的重要手段。本文以鎂鋁合金作為研究對象,采用基于嵌入式原子法的分子動力學方法,針對鎂鋁合金凝固特性以及固液界面結(jié)構(gòu)開展理論計算和實驗研究,相互驗證,以揭示鎂熔體中溶質(zhì)原子對異質(zhì)形核界面的影響機制。利用基于嵌入式原子法的分子動力學方法,采用徑向分布函數(shù)、雙體分布函數(shù)、均方根位移、體系總能量以及VMD分子動力學可視化分析等微觀結(jié)構(gòu)分析與表征方法,對純Mg熔體、Mg-3Al合金、Mg-6Al合金和Mg-9Al合金液固轉(zhuǎn)變過程微觀結(jié)構(gòu)的演化機理進行了分析。當冷卻速率為1×1013K/s時,Mg-3Al合金、Mg-6Al合金和Mg-9Al合金最終都形成了原子排列有序的晶體結(jié)構(gòu),只是初始轉(zhuǎn)變溫度稍有不同,Mg-3Al合金在體系溫度降至497K時已經(jīng)呈現(xiàn)晶體結(jié)構(gòu)特征,Mg-6Al合金和Mg-9Al合金液固轉(zhuǎn)變溫度分別為647K和747K。此外Mg-Al合金中Mg原子跟Al原子之間具有更強的成鍵傾向。均方根位移(MSD)和系統(tǒng)總能量的分析也進一步驗證了徑向分布函數(shù)(RDF)的結(jié)果。通過VMD分子動力學可視化分析可以直觀的觀察到體系的晶化情況,最終體系都形成了原子排列有序的晶體結(jié)構(gòu),并且隨著合金體系中鋁含量的增加,體系的晶化程度也在提高。采用分子動力學方法研究了Mg/Mg-3Al合金體系固液界面的結(jié)構(gòu),通過可視化軟件Ovito記錄了不同時刻的原子位置文件,繪出了所模擬體系原子的位置圖像,從而能夠定性的分析固液界面處原子的排列情況,在溫度調(diào)整到680K時,從5000步開始,雖然Mg-3Al合金區(qū)域原子還是處于無序狀態(tài),但是靠近固液界面處的液體區(qū)域開始呈現(xiàn)一些有序性,并且發(fā)現(xiàn)Al原子有向界面處擴散的趨勢。隨著弛豫時間的增加,基體上半部分靠近固液界面處的幾層原子已經(jīng)出現(xiàn)了一定的有序度,這也跟液體附著在固體基底時的情況一致,并且合金中的Al原子也處于有序排列狀態(tài),占據(jù)著Mg原子的位置。固液共存體系弛豫1200000步后,體系處于兩相平衡狀態(tài),靠近固液界面處的液態(tài)區(qū)域原子存在明顯的有序度。采用OM、SEM和EDS等分析測試手段對鎂合金中初生相與共晶相界面的組織與成分分布進行實驗觀測和分析,討論了Mg晶粒密排面取向?qū)簿L及Al元素分布的影響。結(jié)果表明,不同Mg的密排面跟Mg-9Al合金形成的界面對溶質(zhì)原子分布的影響不一樣,純Mg的(0001)密排面與Mg-9Al合金熔體形成的固液界面更能促進共晶組織的生長,合金液中Al溶質(zhì)元素沿著垂直于固液界面方向的擴散也更活躍。
[Abstract]:Magnesium alloy as green engineering materials in twenty-first Century and potential application value, has good cutting performance, high strength, impact resistance, good damping property and many other advantages, in aerospace materials, military, medicine and chemical industry, metal castings and automotive industry and other fields has been widely used. But because of the plastic and the poor formability of magnesium alloy, limit its application and development. With the continuous innovation and progress in the field of science and technology, on the material properties of the increasingly high demand, the research methods of materials to experiment mainly means there are many limitations, has been difficult to meet the requirements of materials research and development stage, so to explore excellent the performance of new materials has become a trend of new technology by computer simulation. Molecular dynamics simulation can be observed in high speed metal melt solidification process of atoms in micro structure change In the calculation, on the macroscopic properties of the material also has a high degree of accuracy, has gradually become an important means in the field of materials research. In this paper, magnesium alloy as the research object, using molecular dynamics method based on embedded atom method, based on the theoretical calculation and experimental study, carry out the solidification characteristics of magnesium alloy and the solid-liquid interface structure of mutual authentication in order to reveal the influence mechanism of solute atoms in magnesium melt on heterogeneous nucleation interface. Using molecular dynamics method based on embedded atom method, the radial distribution function, pair distribution function, mean square displacement, total energy and VMD molecular dynamics visualization analysis of microscopic structure analysis and characterization methods of pure Mg melt of Mg-3Al alloy. Mg-6Al alloy and Mg-9Al alloy in liquid-solid transformation process of microstructure evolution mechanism is analyzed. When the cooling rate is 1 * 1013K/s, Mg-3Al alloy, Mg -6Al alloy and Mg-9Al alloy are eventually formed the atomic arrangement of crystal structure and orderly, but the initial transition temperature is slightly different, Mg-3Al alloy to 497K temperature in the system has characteristics of crystal structure, Mg-6Al alloy and Mg-9Al alloy in liquid-solid transition temperature were 647K and 747K. in the bond between Mg atom in Mg-Al alloy with Al the atom has stronger. RMS displacement (MSD) and analysis of the total energy of the system is further validated by radial distribution function (RDF). The results by VMD molecular dynamics visualization analysis can be directly observed crystallization system, final system has formed the atomic arrangement of crystal structure and orderly, and with the increase of aluminum content the alloy system, the crystallization degree of the system is also improved. The structure of Mg/Mg-3Al alloy system of the solid-liquid interface by molecular dynamics method, through visual software O Vito has recorded the atomic location file of different time, draw the position image simulation system of atoms, so as to the arrangement of atoms at the solid-liquid interface and qualitative analysis, the temperature adjustment to 680K, from the beginning of the 5000 step, although the Mg-3Al alloy still in the disordered state of atoms, but the liquid region near the solid-liquid interface start showing some order, and found that Al atoms diffuse into the interface of the trend. With the increase of the relaxation time, the matrix layers of atomic part near the solid-liquid interface has been ordered to some extent, it is attached to a solid substrate with the liquid of the line, and the Al atoms in the alloy in the ordered state, occupy the position of the Mg atom. The solid-liquid coexistence system of relaxation after the 1200000 step, the system in the two-phase equilibrium liquid near the region of the atom at the solid-liquid interface are Ming Order of the display. By OM, SEM and EDS analysis method of magnesium alloy in primary and eutectic phase interface microstructure and composition distribution of the experimental observation and analysis, the influence of Mg grain orientation on the close packed plane distribution of eutectic growth and Al elements discussed. The results show that different Mg close packed plane with the formation of Mg-9Al alloy interface is not the same effect on the solute distribution, pure Mg (0001) dense solid-liquid interface surface and the formation of Mg-9Al alloy melt can promote the eutectic growth of Al alloy liquid solute diffusion along the direction perpendicular to the solid-liquid interface are more active.

【學位授予單位】：南昌大學
【學位級別】：碩士
【學位授予年份】：2016
【分類號】：TG292

【參考文獻】

相關(guān)期刊論文 前10條

1 鄧永和;文大東;彭超;韋彥丁;趙瑞;彭平;;二十面體團簇的遺傳:一個與快凝Cu_(56)Zr_(44)合金玻璃形成能力有關(guān)的動力學參數(shù)[J];物理學報;2016年06期

2 周化光;王猛;林鑫;黃衛(wèi)東;;基于臨界晶胚法的Ni固液界面能分子動力學計算[J];稀有金屬材料與工程;2013年06期

3 王利飛;黃光勝;李紅成;張華;;應變速率對AZ31B鎂合金板材組織和成型性能的影響(英文)[J];Transactions of Nonferrous Metals Society of China;2013年04期

4 鄭小青;楊洋;孫得彥;;模型二元有序合金固液界面結(jié)構(gòu)的分子動力學研究[J];物理學報;2013年01期

5 常芳娥;方雯;李娜;董廣志;趙志偉;堅增運;;鋁鎂合金固-液界面能分子動力學模擬與計算[J];西安工業(yè)大學學報;2012年06期

6 堅增運;陳極;常芳娥;曾召;何壇;介萬奇;;銀凝固過程中亞臨界晶核和晶體團簇的分子動力學模擬[J];中國科學:技術(shù)科學;2011年06期

7 丁文江;付彭懷;彭立明;蔣海燕;王迎新;吳國華;董杰;郭興伍;;先進鎂合金材料及其在航空航天領(lǐng)域中的應用[J];航天器環(huán)境工程;2011年02期

8 郭德成;李雙;閆孟澤;趙艷春;李之杰;;C_2團簇在金剛石(111)表面吸附結(jié)構(gòu)的分子動力學模擬[J];計算物理;2011年01期

9 梁永超;劉讓蘇;朱軒民;周麗麗;田澤安;劉全慧;;液態(tài)Mg_7Zn_3合金快速凝固過程中微觀結(jié)構(gòu)演變機理的模擬研究[J];物理學報;2010年11期

10 高廷紅;劉讓蘇;周麗麗;田澤安;謝泉;;液態(tài)Ca_7Mg_3合金快速凝固過程中團簇結(jié)構(gòu)的形成特性[J];物理化學學報;2009年10期

相關(guān)博士學位論文 前2條

1 鄭小青;有序合金固液界面結(jié)構(gòu)和動力學性質(zhì)的分子動力學研究[D];華東師范大學;2012年

2 高玉鳳;典型固液界面熱力學與動力學性質(zhì)的分子動力學研究[D];華東師范大學;2011年

，

本文編號：1426691