低热输入激光沉积颗粒增强铝基复合材料声致界面复合机理

The serious interface reaction is the crucial problem for the laser deposition of particle reinforced aluminum matrix composites, which can badly reduce the mechanical properties. To resolve this issue, a new method by applying non-contact and removable electromagnetic ultrasonic wave into the liquid pool molten by laser with low heat input is proposed here. The interface reactions can be suppressed by reducing laser heat input. After the ultrasonic vibration is applied into the molten pool, the interface between ceramic particles and the liquid Al alloy would be cleaned and activated at relative low temperature, and then direct bonding at the interface can be realized. A mathematical model for coupled ultrasonic field and temperature field in laser molten pool will be established. The effect of ultrasound energy on the physical, chemical and mechanical performance of molten pool will be investigated. The cavitation behavior and regulation mechanism in laser molten pool will be focused. With the effects of ultrasonic cavitation and acoustic streaming, the interfacial behavior between ceramic particles and Al alloy, such as the oxide film removing, wetting, bonding process and mechanical characteristic of the interface, will be illuminated. Under ultrasonic treatment, the relationship of the fracture behavior and mechanical properties of aluminum matrix composites on the interface structure, microstructure and component of deposited layer will be revealed. By optimizing the electromagnetic ultrasonic assisted laser deposited process, a new technical method for additive manufacturing for complicated structure aluminum matrix composites is expected to approach.

针对激光沉积颗粒增强铝基复合材料存在界面化合物导致力学性能严重降低的问题，本项目提出在低热输入的激光沉积方法中施加非接触、可移动式电磁超声波。通过降低激光热输入抑制界面反应，在液态熔池中施加超声振动可清理并活化陶瓷颗粒和液态铝合金的界面，促进陶瓷颗粒与液态铝合金的润湿复合，实现复合材料液固界面的牢固结合。本项目拟通过建立超声波作用下激光熔池声场、温度场耦合数学模型，研究声能对熔池物理、化学及力学性能的作用机制。着重研究激光熔池内的声空化行为及其调控机理，阐明声空化及声流作用下，陶瓷颗粒与铝合金之间去膜润湿过程、界面结合机制及界面力学性能等界面行为。揭示声场条件下，沉积层界面结构、组织状态、合金成分与铝基复合材料断裂行为及力学性能之间的内在规律，优化并完善电磁超声辅助激光沉积工艺，为复杂结构铝基复合材料的增材制造探索新的技术途径。

采用超声波辅助激光熔化沉积法制备了铝硅合金及其SiC颗粒增强铝基复合材料，围绕增材制备试样致密化成形工艺、组织细化机制、合金元素对界面反应的影响及组织与力学性能的关系等方面开展研究，主要取得以下研究成果：(1)模拟了超声振动条件下激光熔化沉积固态母材表面的声压分布特征，探索了超声激励振幅、超声频率及试件尺寸等工艺参数对母材表面振动分布特征的影响规律。(2)研究了激光熔化沉积铝硅合金及其复合材料气孔的形成机理，超声参数、激光参数及粉末物性对孔洞的影响规律，揭示了激光熔池内声致除气机理。(3)研究了硅含量对碳化硅陶瓷颗粒与铝基体界面反应的影响规律，阐明了超声波作用下组织细化机制。(4)分析了制备工艺及工艺参数对沉积层显微硬度、拉伸性能及断口形貌的影响规律，揭示了激光增材工艺-宏观成形-微观组织-力学性能的相互作用关系。这些研究成果均可为高性能铝硅合金及其颗粒增强铝基复合材料的激光增材制备提供必要的理论基础及技术支持。