题目：对高速冷却条件下Al-Si合金动力学相图的探索与发展

报告人：邱冬 高级讲师（RMIT University/皇家墨尔本理工大学）

时间：2024年7月15日（周一）下午2:00

地点：师昌绪楼403会议室

对高速冷却条件下Al-Si合金动力学相图的探索与发展

以激光粉床熔融（L-PBF）为代表的金属增材制造技术，其凝固过程通常伴随远高于砂型铸造的冷却速度(10⁴～10⁶ K/s)。高冷速除了可以细化凝固组织，对凝固组织中的物相组成及其占比也与近平衡凝固条件下有显著的区别。在过去的文献和教科书中，与冷速相关的相变动力学研究主要集中在固态相变，而对凝固过程中的动力学研究相对薄弱，尤其是对近共晶成分下的合金凝固组织缺乏系统性的研究。本工作以近共晶Al-10wt%Si合金为模型合金系统考察了高压压铸（HPDC）条件下和激光粉床熔融条件下凝固组织中出生-Al相与共晶组织的比例，共晶产物的成分，共晶反应的过冷度，以及Si在-Al相中的过饱和固溶度。在此基础上，运用Scheil-Gulliver模型，初步建立了二元Al-Si合金的“动力学相图”以及各个关键参量随冷速变化的经验公式。这些开创性的工作对于在增材制造条件下其它合金凝固组织的预测，组织建模以及性能评估都具有很强的指导意义。

Topic of the report: 

Revisiting the Al-Si phase diagram upon a broad range of cooling rates 

The emerging metal additive manufacturing (AM) usually features a much higher cooling rate during solidification (10⁴～10⁶ K/s) than that in conventional sand casting. The high cooling rate does not only refine the microstructure but can also induce a substantial change on the phase constituents and their fraction, which is far from what is derived from equilibrium phase diagram. Therefore, it poses a great challenge to predict the actual phase constituents and their fraction in the as-fabricated AM components. In this study, a near eutectic Al-10wt%Si model alloy was fabricated using high-pressure die casting (HPDC) and powder bed fusion-laser beam (PBF-LB) processes. After comprehensive microstructure characterization, considerable differences were identified in Al-Si eutectic volume fractions, eutectic Si composition, eutectic undercooling, and the solubility of Si in the Al matrix with the increase of cooling rate. A series of empirical relationships were developed relating to cooling rate and microstructure. Based on the Scheil-Gulliver analysis, a ‘kinetic phase diagram’ is proposed for the Al-Si system to precisely reflect the cooling rate effect on the as-fabricated samples' phase constituents and their constituents. This is an original study that, for the first time, systematically investigated the effect of cooling rate in a wide range (10^-3 to 10⁶ K/s) on the microstructure formation of near eutectic Al-Si alloys. The developed empirical relationships will primarily benefit but not be limited to microstructure modelling, process design, and alloy development when a high cooling rate is accompanied.  

个人简介：

邱冬博士为澳大利亚皇家墨尔本理工大学高级讲师。自2005年起长期从事镁合金、铝合金、锌合金以及铁素体/奥氏体钢等多种工程合金凝固过程中高效晶粒细化剂的开发。2015年开始从事适合增材制造特点的新型工程合金的设计与开发，以及对3D打印过程中微观组织的调控与优化。截止到2023年4月，邱冬博士共主持1项，参与4项澳大利亚自然科学基金课题（ARC Discovery Project）和1项应用创新基金课题（ARC Linkage Project），发表了110篇经同行评议的期刊论文，其中包括1篇发表在Nature上，3篇发表在Nature Communications上，以及18篇发表在国际物理冶金领域知名期刊Acta Materialia上；在Scopus搜索引擎上论文被引用总数达5800余次，H因子为39。来访人之前已经与中国科学院金属研究所杨柯、任玲团队有过合作，在Nature Communications、International Journal of Plasticity等期刊共同发表文章4篇，此次来访中国科学院金属研究所希望就先进钛合金增材制造相关课题展开深入交流，继续深化双方的学术合作。