高性能镁合金纳米混杂复合材料的动态力学行为及细观强韧化机理

Study on dynamic mechanical behavior and strengthening-toughening mechanisms of magnesium alloy based nanocomposites is the new development trends of the deeper research and utilization of lightweight alloys. Carbon nanotubes (CNTs) and silicon carbide (SiC) nanoparticulates hybrid reinforced AZ91 magnesium alloy matrix composites with prominent mechanical properties have been fabricated by self-designed semisolid stirring assisted ultrasonic cavitation and surface modification of nanosized reinforcements in our previous studies.Based on this, the present study will be focused on the dynamic mechanical behavior and strengthening-toughening mechanisms of the magnesium alloy based nanocomposites filled with nanosized hybrid reinforcements.In the experiment,the macroscopic-microscopic tensile behaviors and the effects of temperature and strain rate on the tensile constitutive relation of the magnesium alloy based nanocomposites with different hybrid ratios are investigated. Effect laws of different factors such as hybrid ratios, distribution, surface modification of nanosized hybrid reinforcements, and their interfacial adhesion with magnesium alloy matrix on tensile deformation and tensile failure mechanism are discussed, and the constitutive equation and mechanical property parameters of the heterogeneous nanocomposites are determined. In addition,the effects of interfacial modification on micromechanical behaviors of CNTs and nano-SiC hybrid reinforced magnesium alloy based composites are also considered.In theory and numerical simulation, the effects of different fractal box dimensions, hybrid ratios of nanosized hybrid reinforcements, and the interfacial bond strength of the reinforcements and matrix on the mechanical properties of the hybrid composites are numerically researched by using the actual microstructure-based finite element method according to the fractal and homogenization theory as well as digital image processing technology. Finally, the validity of all kinds of microstructure models will be analyzed and a novel theoretical strengthening-toughening model for nanosized hybrid reinforcements will be established by combining with the results of experiments.The present study is of great theoretic and innovating significance to enrich the theories for metal matrix nanocomposites and to expand the application fields of the lightweight alloys.

镁合金纳米复合材料的动态力学行为及强韧化机理研究是开展轻质合金更深层次研究和应用所面临的挑战。在前期采用自行设计的超声搅拌和纳米材料改性方法，制备出具有优良综合力学性能的碳纳米管和纳米SiC混杂增强AZ91镁合金复合材料。在此基础上拟着重研究该类复合材料的动态力学行为及强韧化机理：在实验上，研究不同纳米混杂复合材料的宏细观拉伸特性及其温度和应变率效应等，探讨不同纳米混杂比、分布和纳米表面改性及界面状况等因素对材料拉伸变形影响规律及其拉伸破坏机理，确定其本构及力学性能参数。在理论和数值模拟方面，运用分形、均匀化理论及数字图像处理技术，通过基于实际微观结构的有限元法，计算研究不同分布维数、混杂比、界面结合等因素对其力学性能影响规律，结合实验分析各种细观结构模型的有效性，并建立一种新型纳米混杂强韧化理论模型。本研究对于丰富纳米复合材料理论和扩展轻质合金应用领域有着重要的意义，且具有明显的创新性。

作为一种新型的轻质纳米复合材料，碳纳米管和纳米碳化硅混杂增强AZ91D镁合金复合材料有可能成为高温高速冲击下汽车和航空航天部件及军事装置的潜在运用材料，镁基纳米复合材料的动态力学行为及强韧化机理问题在复合材料宏细观力学及其多尺度分析中受到了国内外学者的高度重视。我们针对上述问题进行了深入研究。首先，采用电子万能试验机和带有加热装置的分离式霍普金森拉杆实验装置对高能超声辅助半固态搅拌铸造法制备的碳纳米管和纳米碳化硅总体积百分数为1.0 vol%及不同混杂比的AZ91D镁合金基纳米混杂复合材料及其基体镁合金的准静态和高温动态拉伸行为进行了实验研究，获得了温度和应变速率对复合材料动态拉伸响应的影响规律，并基于对原始实验数据的温度修正以及考虑温度与应变率之间的耦合作用拟合得到了在温度处于293～523K、应变率处于0.001/s～2316/s 范围内的修正 Johnson-Cook (J-C) 塑性和破坏本构；基于动态实验数据建立的复合材料应变率和温度耦合的修正本构模型，开发了镁基复合材料J-C本构子程序，采用该子程序进行的霍普金森拉杆数值模拟结果与实验数据吻合得较好；基于复合材料纳米尺度界面本构和动载下细观力学模拟研究成果，提出了纳米复合材料中基体和纳米增强相之间的界面效应、 纳米增强相尺寸效应以及纳米混杂增强体之间的协同作用导致镁合金纳米复合材料的强化，使得其在高温动态拉伸时仍具有较高的动态力学性能，首次建立了纳米尺度的界面特性对动态拉伸响应的定量影响规律；完成了一部有特色的纳米表面工程及力学专著，在国内已被较多地使用。