液锻连挤-熔化激活制备镁基复合材料半固态坯及触变成形研究

Based on the research foundation of the applicant, a new process of preparing magnesium matrix composites semi-solid billets is proposed to promote the application of semi-solid processing in forming magnesium matrix composites. The new process is characterized by liquid infiltration, liquid forging, continuous extrusion, melting activation during partial remelting and thixoforming. The essence of liquid forging plus continuous extrusion is to apply a high pressure on magnesium matrix composites prepared by liquid infiltration. Crystallization and freezing of magnesium matrix composites treated by liquid infiltration are occurred under a high pressure. Once freezing is completed, magnesium matrix composites are subjected to continuous hot extrusion. When the magnesium matrix composites treated by extrusion are reheated to the semi-solid temperature zone for short times, fine and spheroidal solid grains uniformly surrounded by liquid are obtained. The research subjects mainly involves five aspects. They are Al2O3sfoSiCp/AZ91D prepared by liquid forging plus continuous extrusion, designing the integrated device for liquid forging plus continuous and experiment, the formation mechanism of spheroidal solid grains in the semi-solid state and kinetic model, mechanical behavior and rheological behavior of magnesium matrix composites in the semi-solid state and thixoforming. The research meanings is to supply a new process for preparing magnesium matrix composites semi-solid billets and to compensate the shotcomings of present processes for preparing metal matrix composites semi-solid billets. Moreover, the new process is favorable for promoting the application of magnesium matrix composites.

为了推动半固态加工技术在成形镁基复合材料中的应用，申请人在多年研究的基础上，以Al2O3sfoSiCp/AZ91D为研究对象，提出了液锻连挤-熔化激活制备镁基复合材料半固态坯料的工艺方法。液锻连挤的实质是对液态浸渗制备的复合材料施以高压，使其在压力作用下结晶凝固；凝固一旦结束，立即进入挤压变形，使枝晶破碎。当复合材料重新加热到金属基体固液两相区进行短时间保温处理，便可获得均匀、细小的半固态球状组织。触变成形后，即可获得形状复杂、性能优良的镁基复合材料构件。研究内容涉及了浸渗液态模锻法制备复合材料、液锻连挤一体化装置设计与实验、球状组织形成机制及动力学模型研究、复合材料在半固态下的力学行为及流变行为研究、触变成形等五个方面。研究意义在于开辟了一条制备镁基复合材料半固态坯的新途径，弥补现有半固态坯制坯方法的不足，从而丰富半固态成形技术，推动镁基复合材料的广泛应用。

针对镁基复合材料近净成形困难，提出了液锻连挤制备镁基复合材料半固态坯料-触变模锻成形的方法。本项目采用实验法研究了液锻连挤一体化，给出了坯料挤压速率、坯料温度与坯料挤压质量的对应关系；揭示了二次重熔过程中组织演变规律、球状半固态组织的形成机制；建立了半固态组织晶粒长大的动力学方程，给出了晶内液相的形成和迁移的物理模型。采用半固态等温压缩试验，给出了温度、应力与应变的关系，建立了镁基复合材料半固态压缩本构模型，揭示了剪切速率、表观粘度与固相率的对应关系，镁基复合材料半固态坯料呈现出“剪切变稀”的特性。开发了触变模锻成形装备，实现兵器装备壳体、筒体等构件的近净成形。本项目为半固态成形技术在镁基复合材料的应用开辟了新路。