纳米SiC颗粒增强Mg-Al-Si复合材料ECAP过程中多相交互作用及高温蠕变行为研究

Magnesium matrix composites have become the most potential material for aerospace and automotive applications due to their light weight、high strength and high temperature properties. However, the coarse Chinese script type Mg2Si in as-cast Mg-Al-Si matrix composites greatly dissevers the matrix and leads to the decrease of the ultimate tensile strength and the elongation. This detrimental effect is more apparent with the increasing Mg2Si content. While the addition of nano-sized SiC particles (nano-SiCp) can refine the grains of the matrix and Mg2Si, resulting in simultaneous improvement in tensile strengths and elongation. In this project，the nano-SiCp and in-situ synthesized Mg2Si particles co-reinforced magnesium matrix composites with fine grains, uniform particle distribution and higher tensile strengths and elongation was fabricated by adding the nano-SiCp in as-cast Mg-Al-Si matrix composites and combining with equal-channel angular pressing (ECAP) process.The relations of microstructure and mechanical properties of n-SiCp and in-situ synthesized Mg2Si particles co-reinforced magnesium matrix composites after ECAP will be analyzed and Multiphase interaction mechanism during ECAP will be revealed. In addition, the high temperature creep mechanism and creep fracture mechanism of the n-SiCp and in-situ synthesized Mg2Si particles co-reinforced fine grained magnesium matrix composites will be illustrated through the way of investigating its creep property, microstructure evolution during creep and calculating stress exponent and creep activation energy after creep test. The investigation of this project will have important theoretical value on the development, microstructures and mechanical properties control of high strength magnesium matrix composite.

基于轻质高强和优良的高温性能优势，镁基复合材料成为航空航天及汽车等民用行业最具发展潜力的材料。但铸态Mg-Al-Si复合材料中原位自生Mg2Si呈粗大汉字状，严重割裂基体，Mg2Si量越多，力学性能降幅越大，限制了其广泛应用。纳米SiCp能细化晶粒，同时提高材料强塑性。本项目提出在Mg-Al-Si复合材料中添加纳米SiCp，结合等通道转角挤压(ECAP)技术，制备出颗粒细小、分布均匀且强塑性同步提高的细晶镁基复合材料。研究纳米SiCp和原位自生Mg2Si复合增强镁基复合材料ECAP变形后组织与力学性能关系，揭示多尺寸多种类颗粒在ECAP过程中与基体的交互作用机理；研究细晶镁基复合材料高温蠕变性能及蠕变过程中组织演变规律，计算复合材料应力指数和蠕变激活能，阐明多尺寸多种类颗粒增强细晶镁基复合材料的高温蠕变和断裂机制。这对高强镁基复合材料的开发、组织和性能控制，具有重要理论指导意义。

Mg-Al-Si 复合材料由于在镁合金中原位自生引入高温稳定相Mg2Si而具有轻质高强和优良的高温性能优势，成为了为汽车发动机打造的第一代镁基复合材料。但铸态原位自生 Mg2Si 呈粗大汉字状，严重割裂基体，Mg2Si 含量越多，力学性能降幅越大，限制了其广泛应用。而纳米 SiCp 能细化晶粒，同时提高材料强塑性。本项目提出在 Mg-Al-Si 复合材料中添加纳米 SiCp，结合等通道转角挤压 (ECAP)技术，制备出颗粒细小、分布均匀且强塑性同步提高的细晶镁基复合材料。结果表明：制备Mg-Al-Si 复合材料时，Si含量不易超过1%，否则容易出现粗大多角状Mg2Si 颗粒，严重降低复合材料性能。通过半固态搅拌结合超声处理可以顺利实现纳米 SiCp 的引入和均匀分布；添加纳米 SiCp可以有效细化镁基复合材料基体晶粒和Mg2Si 颗粒，使得Mg-Al-Si 复合材料强塑性同时得到提高；等通道转角挤压可显著细化基体晶粒，使Mg-15Al-1Si复合材料基体晶粒由80μm锐减至5.98μm，碎化粗大Mg2Si 颗粒至~3μm微米；纳米 SiCp的添加在ECAP过程中对位错起到有效钉扎作用，可以有效促进等通道转角挤压对基体晶粒的细化（同工艺下基体晶粒26.68µm(Mg9Al-1Si)减小到18.21µm(Mg9Al-1Si-1SiC)）和Mg2Si 颗粒的碎化。微米Mg2Si和纳米 SiCp复合增强的镁基复合材料性能（Mg-9Al-1Si-1SiC：UTS,255MPa、YS,161MPa和δ,7.9%）显著高于单一颗粒增强的复合材料力学性能（Mg9Al-1Si：UTS,242MPa、YS,155MPa和δ,6.2%）;通过计算复合材料的蠕变应力指数 n 及激活能 Q表明，n 伴随温度的上升而增大； Q 伴随应力的增大而增大；4道次等通道挤压的单一Mg2Si增强的ZS32复合材料蠕变机制是位错攀移；微米Mg2Si和纳米 SiCp复合增强的镁基复合材料的应力指数在5.51-6.89之间，在(448~498K)/(70~90MPa)试验条件下，蠕变机制是位错攀移和第二相交互协同作用机制。本项目的研究成果为纳米颗粒增强镁基复合材料的制备和工业应用推广提供了一种可行的实验方法，为高性能镁基复合材料的开发、组织和性能控制提供了实验依据和理论指导。