Tailored formation of novel reinforcement in laser additive manufactured aluminum matrix nanocomposites and its strengthening mechanisms on mechanical properties

陶瓷颗粒增强铝基复合材料（AMC）的显著缺点之一是在强度增加的同时塑性下降。将增强体尺寸减小到纳米尺度是解决AMC强度和塑性之间矛盾的一条很有前途的途径。在本项目中，基于粉末的激光增材制造（LAM）工艺，包括选择性激光熔化（SLM）和激光金属沉积（LMD）应用于处理铝基纳米复合材料通过一个完整的熔化和固化机制。考虑到LAM的高升温速率和高冷却速率的特点以及由此产生的非平衡冶金机制，实现了再析出纳米陶瓷增强体的可控发展和分散。本项目从理论上研究了非平衡Marangoni流作用下激光诱导熔池内温度场、速度场和溶质场及其对纳米陶瓷增强相生长和分散的综合影响，提出了具有独特微观结构和分布特征的纳米增强相的激光控制形成机制。定量研究了增强陶瓷和铝基体的种类和含量、粉末的物理性能以及激光加工工艺参数对纳米陶瓷增强相结晶和生长行为的影响，为获得纳米增强相的可控微观结构提供了材料和工艺方法。研究了激光增材制造AMCs零件的力学性能（特别是拉伸强度和塑性），阐明了纳米增强Al基复合材料的强化机理。一个过程？微结构因此，建立了性能关系，从而能够成功地生产具有定制的增强结构和改善的机械性能的AMC部件。本课题强调“设计材料”、“定制工艺”和“性能可控”的集成，为高性能AMC部件的LAM提供了科学的理论依据和关键策略。

One of the significant drawbacks for ceramic particle reinforced aluminum matrix composites (AMCs) is the decrease of ductility accompanied with the increase in strength. Decreasing the size of reinforcement to nanoscale is a promising approach to solve the contradiction between strength and ductility of AMCs. In the present project, powder-based laser additive manufacturing (LAM) processes including selective laser melting (SLM) and laser metal deposition (LMD) are applied to process Al-based nanocomposites through a complete melting and solidification mechanism. The unique feature of LAM of high heating and cooling rates and resultant non-equilibrium metallurgical mechanism are considered, in order to realize the controllable development and dispersion of re-precipitated nanoscale ceramic reinforcement. This project theoretically studies the temperature, velocity, and solute fields and their combined effect on the growth and dispersion of nanoscale ceramic reinforcing phases within laser-induced molten pool under the action of non-equilibrium Marangoni flow, thereby proposing the laser-controlled formation mechanisms of nanoscale reinforcing phases with unique microstructure and distribution features. The influence of the category and contents of reinforcing ceramics and Al-matrix, the physical properties of powder, and the applied laser processing parameters on the crystallization and growth behaviors of nanoscale ceramic reinforcing phases is quantitatively studied, in order to propose the material and process methods to obtain the controllable microstructures of nanoscale reinforcement. The mechanical properties (especially tensile strength and ductility) of laser additive manufactured AMCs parts are studied and the underlying strengthening mechanisms of nanoscale reinforcement to Al-matrix are elucidated. A process¿microstructure¿performance relationship is accordingly established to enable the successful production of AMCs parts with tailored reinforcement architecture and improved mechanical performance. The integration of 'designed material', 'tailored process', and 'controllable performance' is emphasized in this project, providing the scientific theoretical basis and key strategy for LAM of high-performance AMCs components.