剩余液相在金属半固态加工过程中的二次凝固行为与作用机理

According to the theory of solidification, the products without porosity defects can be obtained by semisolid processing because of its particular solidification process of the non-dendritic. The secondary solidification process of semisolid alloy with half solid and half liquid influences significantly on the formability, microstructure, defects and properties of final products. According to particularity of different alloy system in secondary solidification process, the secondary solidification behavior of remnant liquid of the semisolid alloys during semisolid processing will be focused in this project, which the alloys include solid solution alloy, hypo-eutectic alloy, and peritectic alloy.The thermal simulator and change of solidification path are used in the experiments. So the solidification process and resulting microstructure of the remnant liquid will be investigated of the three types of alloy under quasi-equilibrium and non-equilibrium condition with varied solid liquid fraction ratio, cooling rate, and forming condition. Then the relationship between microstructure of secondary solidification and mechanical properties will be also explored. Besides, the nucleation of primary solid phase, growth stability of interface between the primary solid phase and the remaining liquid, the diffusion and distribution behavior of the solute during the secondary solidification of semisolid alloys will be also focused on the theoretical research, and the influence mechanism of solid/liquid fraction, solidification route on the secondary solidification behavior of remnant liquid will be investigated. So that the real effect of remnant liquid on formability, microstructure and properties of the semisolid alloys will be also revealed. Subsequently, the obstacle and bottleneck of application of semisolid processing in the industrial application will be solved, and then the research results will be introduced into the optimization and regulation for semisolid processing. Finally, the project will provide a reliable theory and experimental date for the production of precision component and microstructure control with semisolid processing technology in the industrial production.

半固态金属成形以其特殊的非枝晶凝固方式，理论上可获得无孔洞类缺陷的产品。具有一半固相和一半液相的半固态合金的二次凝固对成形性、组织、缺陷和性能都有非常重要的影响。针对不同合金体系在二次凝固过程中的特殊性，本项目以固溶、亚共晶和包晶合金半固态成形过程中剩余液相的二次凝固行为为研究对象，采用热模拟机和凝固路径改变等技术手段，研究三类合金在准平衡和非平衡条件下浆料固液相体积比、冷却速率和成形条件下剩余液相的二次凝固过程和组织，探讨二次凝固组织与力学性能之间的关系；以半固态浆料在二次凝固中初生固溶体相形核与长大的界面稳定性、溶质扩散与再分配行为为重点，研究固液相体积比、凝固路径对剩余液相二次凝固行为的影响机制，揭示剩余液相对半固态合金成形性、组织、性能的真实作用。在理论上解决半固态成形推广应用的障碍和瓶颈，并将其引入半固态成形工艺的优化调控中，为获得精密零件及组织控制提供理论和实验依据。

针对不同合金体系在半固态成形过程的二次凝固过程中的特殊性，本项目以固溶、亚共晶和包晶合金半固态成形过程中剩余液相的二次凝固行为为研究对象，采用热模拟机和凝固路径改变等技术手段，研究了固液相体积比、冷却速率和成形条件对三类合金半固态浆料二次凝固过程的影响规律，以及浆料在准平衡和非平衡条件下的凝固行为，探讨了凝固组织与铸件力学性能之间的关系。并研究了固液相体积比、凝固路径对剩余液相二次凝固行为的影响机制，揭示了剩余液相对半固态合金成形性、组织、性能的真实作用。为工业实践采用半固态成形技术获得良好组织和精密零件提供理论和实验依据，对优化半固态成形工艺设计、提高金属半固态成形件力学性能具有一定的指导意义。