喷射沉积连续挤压制备高硅铝合金的微观组织演变及强化机制研究

Hypereutectic Al-Si alloys are attractive candidate materials for automotive, aerospace and electronics applications due to their excellent properties, such as high strength to weight ratio, high wear resistance, and low coefficient of thermal expansion. Spray deposition has been considered to be more suitable for the manufacture of such materials than other methods, and hot extrusion is usually used to densify the spray deposited preform. However, in the case of high alloying levels, large amount of hard and non-deformable particles restricts the movement of dislocations, hence, plastic deformation becomes difficult. Spray Conform (SC), a novel near net shape process will be used to manufacture Al-20Si-5Fe alloy in this project. That is, liquid metals are atomized into small droplets by inert gas and deposited into the groove of the extrusion wheel, and then, the deposited preform at high temperature is directly extruded by continuous extrusion machine. The combination of finite element simulation and experimental study will be used to study the formation and evolution of the microstructure of the alloy during SC in order to achieve the precise control of microstructure. Tensile property of the alloy will be investigated. With the result, the effect of the microstructure on the tensile property and the strengthening mechanism of the alloy will be researched. The project will reveal the formation mechanism of microstructure of high-silicon aluminum alloy prepared by SC, the nature of alloy strengthening, and the correlation among process parameters and microstructure and mechanical properties. The study on the preparation of hypereutectic Al-Si alloy has important academic significance and practical value. It will promote the development of SC, and provide a scientific basis for the continuous preparation of high performance alloy.

高硅铝合金具有比强度高、耐磨性好且热膨胀系数小等特点，广泛应用于汽车、航天和电子工业。采用喷射沉积法制备此类合金时，易出现因形变能力差而使沉积坯致密化困难的问题。本项目拟采用喷射沉积连续挤压新技术制备Al-20Si-5Fe合金，即将合金熔液喷射沉积在连续挤压机轮槽内，处于高温状态的沉积坯直接经连续挤压形成高致密的铝硅合金。采用有限元模拟与实验研究相结合的方法，研究合金在喷射沉积连续挤压过程中微观组织的形成及演变规律，以实现对合金微观组织的精确控制。研究合金的拉伸性能，结合基体组织和第二相特征，研究显微组织对拉伸性能的影响，以及合金的强化机制。项目将揭示高硅铝合金在喷射沉积连续挤压过程中微观组织的形成机制，以及合金强化的本质，并建立工艺-组织-性能间的关联。项目研究成果对高合金材料的制备具有重要的学术意义和实际应用意义，将促进喷射沉积连续挤压技术的发展，为高性能合金的连续制备提供科学依据。

高硅铝合金具有比强度高、耐磨性好且热膨胀系数小等特点，广泛应用于汽车、航天和电子工业。项目采用喷射沉积连续挤压（spray Conform, SC）新技术制备系列高硅（高铁）铝合金，系统研究了熔体温度、雾化气体压力和挤压比等对高硅铝合金微观组织及性能的影响，研究了合金在SC过程中微观组织的形成及演变规律，测试了合金的拉伸性能和磨损性能，并结合第二相特征研究了显微组织对拉伸性能和耐磨性能的影响，以及合金的强化机制和磨损机制。.研究表明，在采用SC法制备高硅铝合金时，合适的雾化气体压力为0.2-0.4MPa；当Si含量超过25%，或Fe含量超过3%（Si含量为20%）时，挤压比应小于4；SC态Al-20Si-5Fe合金的微观组织与平衡凝固组织和传统喷射沉积组织均不相同：富铁相主要为呈板条状的亚稳相δ-Al9FeSi3，初晶硅相呈颗粒状或块状且含有Al和Fe元素，共晶硅相和ɑ-Al基体中的成分也偏离了平衡状态；呈颗粒状的共晶硅相和尺寸细小的初晶硅相可抑制合金的过早失效，利于将高硅铝合金的抗拉强度极大值推向更高的硅含量；SC法制备的高硅铝合金的强度水平介于挤压铸造和快速凝固制品之间，其主要强化机制为硅相（初晶硅和共晶硅）引起的弥散强化，以及由铝基体与硅相间热膨胀系数的差异引起的热失配强化；细小、规整且分布均匀的硅相不仅会增加高硅铝合金的硬度水平，也会降低其磨损率和摩擦系数，SC态高硅铝合金的主要磨损机制为磨粒磨损和剥层磨损。.项目研究成果对高合金材料的制备具有重要的学术意义和实际应用意义，并将促进SC技术的发展，为高性能合金的连续制备提供科学依据。