选区激光熔化增材制造专用高强度Al-Mg-Sc-Zr合金成分设计及性能调控

The additive manufacturing of traditional aluminum alloys usually exhibit metallurgical defects, unfavorable mechanical property and low plasticity, which induce a long-time puzzled technical bottleneck for the application of additive manufacturing in lightweight field, such as aerospace etc. Breaking through the conventional thinking of fine-grain strengthening of additive manufacturing aluminum alloys, this project proposes developing Sc containing aluminum alloys with excellent strength and toughness by synergetic nano-precipitation and fine-grain strengthening. The applicant has already developed Al-Mg-Sc-Zr alloy with tensile strength 460MPa but there exists cracks in printed sample. Based on this difficulty, this project plans to disclose the effecting mechanism of alloy composition on the crack-sensitivity by combinations of calculations of phase diagram and crack-sensitivity and experimental research, then the anti-crack composition is anticipated to be obtained. Based on this basis, the project plan to illuminate the effecting mechanisms of rare earth microalloying, such as Sc, Zr ect on the nano-sized Al3(Sc, Zr) precipitation behavior and the grain refinement mechanism; then clarify the strength and plasticity synergetic improving mechanisms by nano-precipitation and grain refinement, in order to obtain the alloy compositional designing theory of high-strength aluminum alloys with tensile strength exceeding 530MPa and tensile ratio surpassing 12%. Over all, this project will develop prototypes from alloy compositional design, powder atomization preparation to shaping technology with international advanced level for powder-bed additive manufacturing.

传统牌号铝合金粉末床增材制造极易产生冶金缺陷、性能不高、塑性低，已成为长期困扰增材制造在航空航天等轻量化高强度复杂构件应用的技术瓶颈。本项目打破传统铝合金增材制造仅靠细晶强化的单一思路，提出开发基于细晶与纳米析出协同强韧化的SLM专用含钪高强铝合金。本项目在前期已开发出打印态拉伸强度460MPa的Al-Mg-Sc-Zr基础上，从激光熔池易裂的难点出发，通过相图和裂纹敏感因子计算，揭示合金成分对裂纹敏感性的影响机制，结合实验获得抗裂的合金成分区间；在此基础上阐明Sc、Zr等稀土微合金化设计对纳米Al3(Sc,Zr)相析出特征的影响行为，以及晶粒细化机理；探明纳米析出与晶粒细化对增材制造构件强度-塑性协同提升机制，获得拉伸≥530MPa、延伸率≥12%超高强度铝合金成分设计原理，发展具有国际先进水平的粉末床增材制造专用Al-Mg-Sc-Zr合金粉体成分设计、雾化制备及构件成形技术原型。

增材制造高强度铝合金构件在航空航天和轨道交通等轻量化复杂结构装备上应用广泛。增材制造低钪含量的铝镁合金易产生裂纹缺陷，且强度和塑性等综合力学性能有待提升。本项目围绕裂纹形成机理与阻裂、非平衡组织演化机理、力学性能调控三个方面开展研究。第一，揭示了SLM增材制造Al-Mg合金热裂行为及形成机理，阐明了Mg和Si元素添加及含量对裂纹的影响规律，计算了裂纹敏感因子，通过晶粒细化和降低裂纹敏感性抑制裂纹，获得了无裂纹SLM增材Al-Mg-Sc合金配方。该原理在SLM增材2系与7系合金的阻裂方面也显示出一定适用性。第二，在阻裂基础上进一步调整成分，SLM制备Al-Mg-Sc合金具有超细尺寸胞(胞直径300-600 nm)和胞内共格Al3(Sc,Zr)纳米颗粒(2-15 nm)。在胞状亚晶界或柱状亚晶界处形成直径为10-100 nm的Al-Mg2Si共晶。开展了SLM增材Al-Mg-Sc合金在不同温度、时间的热处理实验，采用TEM观测了纳米析出相种类、尺度及分布规律。第三，系统研究了SLM增材Al-Mg-Sc合金纳米析出强化行为，揭示纳米析出规律对力学性能影响行为。开发的一种钪含量0.5wt%高强度铝镁合金热处理后抗拉强度超过530MPa，屈服超510MPa，延伸率超12%。进一步降低Sc含量至0.3wt%，其抗拉强度达493MPa，屈服达391Mpa，延伸率为13%。设计了1-3 wt. % TiC改性Al-Mg-Sc复合粉末，定向能量沉积样品拉伸强度为354.95-361.51MPa，伸长率为10.46-14.10%。采用气雾化制备出了高品质粉体并打印出合格铝合金零件，在轨道交通、航天和增材制造企业取得了应用或应用验证。