高强铝锂合金的激光选区熔化成形关键技术基础研究

Aluminum-lithium alloy, with high strength and widespread application prospect, is a perfect kind of alternate for traditional high strength aluminum alloy. Selective laser melting (SLM) is a promising method to provide a rapid integrated manufacturing method for them. However, the Al-Li alloy is easy to oxidize, has great hot cracking susceptibility and contains lots of burning alloy elements. Therefore, fabrication of Al-Li alloy with high power laser suffers from high porosity, cracking, burning loss of elements and decrease of strength. Under such condition, the SLM of Al-Li alloy is very difficult and the properties of the fabricated parts are hard to control. This project is proposed to reveal the key technologies, including the interaction mechanism of laser & Al-Li alloy powder, characteritics of the molten pool flowing, solidification microstructure and formation mechanism of metallurgical defects, heat treatment technology by investigating the unsteady interaction between laser and Al alloy powder. By using the technolgies, such as, baking powder for twice in vacuum and taking the diluted plasma to protect the molten pool and the high temperature metal to eliminate the hazard of oxidization generated in the process, using preheating and short line-segment scanning to extend the life time of the molten pool to reducing the formation of gas hole, taking strictly control measure of oxygen content in the gaseous environment and adding trace elements to inhibit the formation of hot crack, homogenizing the laser energy distribution in the laser spot and alloy composition design to reduce the burning loss of the alloying elements, the fabrication of Al-Li alloy using SLM is expected to be successful and the properties of fabrication parts are expected to be controlled.

高强铝锂合金是新一代取代高强铝合金的理想材料，应用前景广泛。激光选区熔化成形技术（Selective Laser Melting，SLM）有望为其复杂零件提供一种整体高精度制造方法。但铝锂合金在高功率激光作用下极易产生气孔、裂纹、元素烧损和强度下降等问题，控形控性难度大。本项目通过研究激光与Al-Cu-Li铝锂合金粉末的非定常相互作用，揭示其相互作用机制；通过研究高斯光束和均匀光束下SLM成形的熔池流动特性、非平衡凝固组织及冶金缺陷形成机理及控制方法，热处理技术及其对性能影响等关键技术，实现SLM成形和质量控制。拟采用真空二次烘焙和稀薄等离子体“保护”等方法来减少粉末氧化和成形气氛氧化的危害、预热和短线段扫描来延长熔池存在时间以减少气孔、严格控制气氛中的氧含量和微合金化技术来抑制热裂纹、采用均匀光斑和合金元素预补偿来调控合金元素的烧损等技术方案，实现高强铝锂合金的SLM良好成形和性能控制。

将铝锂合金与激光选区熔化（selective laser melting，SLM）成形技术结合制造复杂零件，可以同时结合轻质材料和轻质结构的优点，实现双重轻量化的效果。针对SLM成形铝锂合金裂纹敏感性高的问题，本项目建立了SLM成形2195铝锂合金裂纹敏感性模型，理论分析了工艺参数对裂纹形成的影响，最终获得了无裂纹且致密的优化工艺参数，实现了高性能成形。针对SLM成形2195铝锂合金沉积效率低的问题，开展了基于变质处理的SLM成形高强铝锂合金成分设计研究，采用铸造工艺和激光表面工程技术，快速且低成本地得到了抗裂效果好、沉积效率高的新型铝锂合金粉末。针对该新型铝锂合金粉末，研究了其SLM成形的非平衡凝固组织，阐明了变质处理对显微组织和力学性能的影响，并建立其基本热处理工艺规范，其综合性能在现有高强铝合金增材制造领域处于领先水平。本项目为铝锂合金的SLM成形研究奠定理论基础并提供关键技术支撑，有望在航空航天等轻量化需求高的领域获得广泛应用。