【作者】 李黎；

【导师】 李建国；

【作者基本信息】 清华大学 ， 材料科学与工程， 2005， 硕士

【摘要】 针对目前国际上对于低成本 AlTiC 中间合金细化剂的迫切需求及传统制备办法中存在的问题,本文采用新的思路,在制备过程中引入超声场,以 99.7%工业纯铝、石墨和工业氟钛酸钾为主要原料,在低温下快速合成 TiC 粒子,并意图通过超声场的空化效应和声流效应影响 AlTiC 的组织,以实现促进细化剂合成过程和改善 TiC 团聚程度的双重目的。对经同一工艺条件制备的细化剂,用JSM-6301 场发射扫描电镜对合成反应各阶段的 AlTiC 中间合金样品进行了显微组织观察和 EDS 能谱分析,并与未经过超声处理的样品进行了对比分析;将AlTiC 中间合金细化剂添加到 99.8%纯铝中,并进行晶粒细化效果和形核核心的对比观察。在 TiC 合成热力学条件和动力学机制研究的基础上,本文使用扫描电镜和透射电镜观察了TiC 粒子在制备过程中不同阶段的形态,并提出证据证明 K₂TiF₆与石墨在铝液中直接反应是 TiC 粒子的主要生成机制。在超声场制备 AlTiC 中间合金的基础上,本文通过成分控制和组织控制不断探索具有理想细化效果的合金制备工艺。成分控制是组织控制的基础,其中 C的加入是成分控制中最困难也是最关键的一步,它成为 AlTiC 中间合金制备以及推广应用的最大制约因素。通过改变石墨的原始粒度和添加量,研究了这些因素对中间合金组织和细化性能的影响。通过添加 Mn、Cr 等元素,制备出多种 Al-Mg-Si 系合金;并获得了此系列自制合金的力学性能;用透射电镜研究了 Mg、Si、Mn 和 Cr 等元素对本系列Al-Mg-Si 合金组织和性能的影响;测定出 β ’’相和锰铬析出物的晶体结构,并初步探讨了 β ’’相的析出机制。更多还原

【Abstract】 Based on the demand for low-cost AlTiC alloys and benefited fromresearch work of my predecessors, an innovative method was designed forpreparing AlTiC master alloy under ultrasonic field as well as low melttemperature (1073K-1173K), using 99.7% commercial alloy, graphite andK2TiF6. The introduction of ultrasonic vibrations into melt facilitates thesynthesis process of AlTiC and disperses the agglomeration groups composedby TiC particles. The preparation process of AlTiC master alloy wasinvestigated by SEM with EDS. The effectiveness of ultrasonic field wasconfirmed by the comparison of grain refining efficiency of 99.8%commercial aluminum. Also, experiment results indicate that direct reactionbetween Carbon and K2TiF6 dominated the TiC synthesis process compared toother reaction models.Towards to the further improvement of refining ability, the AlTiCfabrication process was optimized through the control of graphite amount andsize, because C addition has been proved to be crucial for this synthesisprocess. Analysis was performed on the influence of graphite size andamount.Part of thesis was focused on the effect of alloy composition onprecipitates of the Al-Mg-Si alloys refined by AlTiC. The influence of Si, Mg,Mn, Cr additions on alloy microstructure and properties was analyzed usingTEM and HRTEM. The crystal structures of precipitates in Al-Mg-Si alloyswere determined by selected area diffraction pattern and fast Fouriertransforms pattern. The precipitation sequence of various kinds of metastablephases in Al-Mg-Si alloy was discussed.更多还原