本文選題：AZ91鎂合金 + 快速凝固　； 參考：《南昌航空大學(xué)》2017年碩士論文

【摘要】：隨著傳統(tǒng)結(jié)構(gòu)材料朝輕量化、綠色化的方向發(fā)展,鎂合金憑借低密度、高比強度/比剛度及良好的阻尼性能等一系列優(yōu)點,廣泛應(yīng)用于航空航天、汽車電子等領(lǐng)域。然而傳統(tǒng)鑄態(tài)方法得到的鎂合金,普遍存在枝晶粗大、成分偏析、縮孔縮松等缺陷,限制了鎂合金在工業(yè)生產(chǎn)中的應(yīng)用。晶粒粗大及高溫晶界β相容易粗化是造成各種缺陷的首要原因。細化晶粒能夠提高合金高溫強度、抗蠕變性,降低組元偏析,抑制β脆性相粗大。因此,深入研究快冷鎂合金細晶組織制備工藝至關(guān)重要,分析微米及納米SiC顆粒參與銅�？炖銩Z91鎂合金的相關(guān)細化機理,以及揭示其對細晶合金高溫條件下晶粒長大行為的影響,對高性能鎂合金的制備具有重要價值。本文采用SiC顆粒孕育劑與快速凝固技術(shù)相結(jié)合的方式,研究了不同粒徑及含量SiC顆粒參與對快冷鎂合金細晶組織形貌和平均晶粒尺寸的影響,獲得鎂合金最優(yōu)細化方案。通過不同溫度與保溫時間固溶處理,結(jié)合合金顯微硬度分析,進一步研究SiC顆粒參與對快冷細晶鎂合金晶粒長大行為的影響。探討細晶合金高溫組織熱穩(wěn)定性,為合金高溫性能的改善提供理論依據(jù)。晶粒細化實驗表明,比常規(guī)凝固,銅�？炖浜辖鸾M織粒狀晶粒細小均勻。微米Si C顆粒的參與導(dǎo)致鎂合金凝固組織進一步細化,含量越高,細化效果越明顯,銅模內(nèi)徑2mm時,亞快速凝固AZ91+2wt%SiC(μm)細化效果最好。微米SiC顆粒促進銅�？炖銩Z91合金異質(zhì)形核,隨著凝固過程進行,多余SiC顆粒被推移到晶界處,釘扎晶界阻礙初生晶粒長大,從而合金組織更加細小彌散。并且微米SiC參與以及銅模內(nèi)徑的降低,快冷鎂合金顯微硬度得到顯著提高,其中當銅模內(nèi)徑2mm,微米SiC含量2wt%時,硬度值高達146Hv,相比鑄態(tài)提高92%。納米SiC顆粒參與下鎂合金顯微組織明顯細化,當納米SiC含量在1wt%時,銅�？炖浜辖鹌骄Я３叽缂毣�5μm,細化效果明顯優(yōu)于微米SiC參與下的快冷鎂合金。納米Si C顆粒在細晶組織中,一方面在晶體內(nèi)部提供異質(zhì)形核,另一方面出現(xiàn)在晶界邊緣釘扎晶界阻礙晶粒長大。固溶處理實驗表明,保溫2h,320℃、370℃時快冷鎂合金不完全固溶,400℃時處于完全固溶狀態(tài)。微米SiC顆粒參與,400℃固溶處理保溫時間由2h延長到8h,亞快速凝固AZ91+2wt%SiC合金平均晶粒尺寸由13μm僅增加到22μm,高溫條件下鎂合金晶粒異常長大得到有效抑制。微米SiC顆粒的存在,其對高溫晶界遷移過程中的釘扎效應(yīng),進一步提高了快冷合金組織熱穩(wěn)定性。細晶鎂合金經(jīng)固溶處理,晶界處離異共晶β相消失,合金硬度值下降。但亞快速凝固AZ91+2wt%SiC合金經(jīng)400℃+8h固溶處理后,組織中析出β-Mg17Al12沉淀相,提高了合金平均硬度值,最高可達111Hv,比同等條件下未添加微米SiC顆粒的AZ91合金提高了63.2%。
[Abstract]:With the development of traditional structural materials in the direction of lightweight and green, magnesium alloys have been widely used in aerospace, automotive electronics and other fields with a series of advantages such as low density, high specific strength / specific stiffness and good damping performance. However, the traditional as-cast magnesium alloy has many defects such as coarse dendrite, composition segregation, shrinkage porosity and so on, which limits the application of magnesium alloy in industrial production. Grain size and high temperature grain boundary 尾 -phase coarsening are the primary causes of various defects. Grain refinement can improve the high temperature strength, creep resistance, reduce segregation of components and inhibit the coarse 尾 -brittle phase. Therefore, it is very important to study the preparation process of fine grain structure of rapidly cooled magnesium alloy. The mechanism of micron and nanometer SiC particles involved in the refinement of AZ91 magnesium alloy is analyzed. It is of great value for the preparation of high performance magnesium alloys to reveal its influence on the grain growth behavior of fine grained alloys at high temperature. In this paper, the effects of different particle size and content of SiC particles on microstructure and average grain size of rapidly cooled magnesium alloy were studied by combining SiC particle inoculant with rapid solidification technology. The optimal refinement scheme of magnesium alloy was obtained. The effect of SiC particles on the grain growth behavior of rapidly cooled magnesium alloys was further studied by solution treatment at different temperatures and holding time, combined with microhardness analysis. The thermal stability of fine-grained alloy at high temperature is discussed, which provides a theoretical basis for improving the high-temperature properties of the alloy. The grain refinement experiments show that the microstructure of the alloy is fine and uniform compared with that of conventional solidification. The participation of micron sic particles leads to further refinement of solidified microstructure of magnesium alloys. The higher the content, the more obvious the refining effect is. The subrapid solidification AZ91 2wt sic (渭 m) has the best refining effect when the internal diameter of copper die is 2mm. The micron SiC particles promote the heterogeneous nucleation of rapidly cooled AZ91 alloys in copper mold. With the solidification process, the superfluous SiC particles are moved to the grain boundaries, and the grain boundaries are pinned to prevent the primary grains from growing, thus the microstructure of the alloy becomes more fine and dispersed. With the participation of micron SiC and the decrease of the inner diameter of copper die, the microhardness of rapidly cooled magnesium alloy was significantly improved. When the copper die diameter was 2mm and the micron SiC content was 2wt%, the hardness value was up to 146Hv, which was 92HV higher than that of as-cast magnesium alloy. The microstructure of magnesium alloy was obviously refined with the participation of nanometer SiC particles, and the average grain size of rapidly cooled copper mold alloy was 5 渭 m when the content of nanometer SiC was 1 wt%, which was better than that of rapidly cooled magnesium alloy with micron SiC. Nanocrystalline sic particles in fine grain structure provide heterogeneous nucleation in the crystal on the one hand, and pinning grain boundary at the grain boundary on the other, hinders grain growth. The experimental results of solid solution treatment show that the rapidly cooled magnesium alloy is in the state of complete solution at 400 鈩，

本文編號：1970694