碳化硅颗粒参与下快冷镁合金细晶组织制备及热稳定性研究

发布时间：2018-06-03 00:05

  本文选题：AZ91镁合金 + 快速凝固　； 参考：《南昌航空大学》2017年硕士论文

【摘要】：随着传统结构材料朝轻量化、绿色化的方向发展,镁合金凭借低密度、高比强度/比刚度及良好的阻尼性能等一系列优点,广泛应用于航空航天、汽车电子等领域。然而传统铸态方法得到的镁合金,普遍存在枝晶粗大、成分偏析、缩孔缩松等缺陷,限制了镁合金在工业生产中的应用。晶粒粗大及高温晶界β相容易粗化是造成各种缺陷的首要原因。细化晶粒能够提高合金高温强度、抗蠕变性,降低组元偏析,抑制β脆性相粗大。因此,深入研究快冷镁合金细晶组织制备工艺至关重要,分析微米及纳米SiC颗粒参与铜模快冷AZ91镁合金的相关细化机理,以及揭示其对细晶合金高温条件下晶粒长大行为的影响,对高性能镁合金的制备具有重要价值。本文采用SiC颗粒孕育剂与快速凝固技术相结合的方式,研究了不同粒径及含量SiC颗粒参与对快冷镁合金细晶组织形貌和平均晶粒尺寸的影响,获得镁合金最优细化方案。通过不同温度与保温时间固溶处理,结合合金显微硬度分析,进一步研究SiC颗粒参与对快冷细晶镁合金晶粒长大行为的影响。探讨细晶合金高温组织热稳定性,为合金高温性能的改善提供理论依据。晶粒细化实验表明,比常规凝固,铜模快冷合金组织粒状晶粒细小均匀。微米Si C颗粒的参与导致镁合金凝固组织进一步细化,含量越高,细化效果越明显,铜模内径2mm时,亚快速凝固AZ91+2wt%SiC(μm)细化效果最好。微米SiC颗粒促进铜模快冷AZ91合金异质形核,随着凝固过程进行,多余SiC颗粒被推移到晶界处,钉扎晶界阻碍初生晶粒长大,从而合金组织更加细小弥散。并且微米SiC参与以及铜模内径的降低,快冷镁合金显微硬度得到显著提高,其中当铜模内径2mm,微米SiC含量2wt%时,硬度值高达146Hv,相比铸态提高92%。纳米SiC颗粒参与下镁合金显微组织明显细化,当纳米SiC含量在1wt%时,铜模快冷合金平均晶粒尺寸细化至5μm,细化效果明显优于微米SiC参与下的快冷镁合金。纳米Si C颗粒在细晶组织中,一方面在晶体内部提供异质形核,另一方面出现在晶界边缘钉扎晶界阻碍晶粒长大。固溶处理实验表明,保温2h,320℃、370℃时快冷镁合金不完全固溶,400℃时处于完全固溶状态。微米SiC颗粒参与,400℃固溶处理保温时间由2h延长到8h,亚快速凝固AZ91+2wt%SiC合金平均晶粒尺寸由13μm仅增加到22μm,高温条件下镁合金晶粒异常长大得到有效抑制。微米SiC颗粒的存在,其对高温晶界迁移过程中的钉扎效应,进一步提高了快冷合金组织热稳定性。细晶镁合金经固溶处理,晶界处离异共晶β相消失,合金硬度值下降。但亚快速凝固AZ91+2wt%SiC合金经400℃+8h固溶处理后,组织中析出β-Mg17Al12沉淀相,提高了合金平均硬度值,最高可达111Hv,比同等条件下未添加微米SiC颗粒的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，

本文编号：1970694