【作者】 梁立超；

【导师】 刘正； 姚建强；

【作者基本信息】 沈阳工业大学 ， 材料工程， 2006， 硕士

【摘要】 本文以AZ91镁合金为基体,并以平均颗粒尺寸2μm的SiC颗粒为增强相,采用全液态搅拌铸造法制备了颗粒增强镁基复合材料SiC_P/AZ91。通过对不同加工处理状态包括铸态、固溶态、固溶+时效态、热挤压态的SiC_P/AZ91复合材料的力学性能测试以及显微组织观察,并利用扫描电子显微镜和x-射线衍射等检测手段对复合材料进行断口分析和相分析,研究了基体晶粒大小和析出相的变化以及增强相颗粒在基体中的分布,探讨了SiC_P/AZ91复合材料的增强机制、耐磨损机理以及拉伸断裂行为。 显微组织观察结果表明,加入微米尺度的SiC增强颗粒明显细化了AZ91基体合金的晶粒,增强颗粒较均匀地分布在基体中。铸态SiC_P/AZ91复合材料在不同实验温度下的抗拉强度和屈服强度均高于铸态AZ91基体镁合金的,相应的SiC颗粒增强机理主要是初生α-Mg相在SiC颗粒表面非均质形核及SiC颗粒阻碍初生α-Mg相生长而对基体产生的细化以及基体合金中的位错增殖机制;SiC_P/AZ91复合材料经过热处理后其在不同实验温度下的抗拉强度和屈服强度均有所提高,尤其是经过固溶+时效处理后,强度的提高更为明显;对铸态SiC_P/AZ91复合材料进行热挤压亦可显著提高复合材料的室温、高温抗拉强度和屈服强度,而且热挤压后的复合材料在高温时仍可保持相当高的抗拉强度和屈服强度;与AZ91基体合金相比,SiC_P/AZ91复合材料表现出更好的室温耐磨损性能;此外,SiC_P/AZ91复合材料的延伸率较小,而且受实验温度的影响不明显,即使在200℃的实验温度下,SiC_P/AZ91复合材料的延伸率仅比室温下的略有增加。 拉伸断口形貌观察与分析显示,SiC_P/AZ91复合材料的低温拉伸断口主要由解理面和撕裂棱组成,具有明显的脆性断裂的特征,而在较高实验温度下,复合材料的拉伸断口主要由解理台阶、撕裂棱和小尺寸的韧窝组成,表现为韧脆混合断裂特征。更多还原

【Abstract】 The SiCp/AZ91 magnesium matrix composite, i.e. AZ91 magnesium alloy reinforced by SiC particulates with average sizes of 2 μm, has been fabricated using fluxless casting technique. Mechanical properties of the SiCp/AZ91 composite at different temperatures and under various hot processed conditions including as-cast, solution treatment, solution plus aging treatment, hot-extrusion were determined. Microstructures of the SiCp/AZ91 composite with different hot processed statuses were observed. Analysis on the tensile fracture surfaces and phase constituent of the SiCp/AZ91 composite was performed by scanning electron microscope and x-ray diffraction technique. Subsequently, the change in grain size and precipitate of the AZ91 matrix alloy as well as the distribution of reinforcing particulates in the matrix were studied. The particulate reinforcing and wear-resistant mechanism as well as tensile fracture behavior in the SiCp/AZ91 magnesium matrix composite was investigated and discussed.The observations on the microstructures showed that the addition of SiC particulates could considerably refine the grains in the AZ91 alloy matrix, and the distribution of the SiC particulates in the matrix was very homogenous. It was found that both ultimate tensile and yield strengths of as-cast SiCp/AZ91 composite at different testing temperatures were higher than those of as-cast AZ91 matrix alloy. There are two kinds of strengthening mechanism in particulate reinforcing magnesium composites. One is refinement of matrix grains caused by both heterogeneous nucleation of a-Mg phase on the surface of the SiC particulates and prohibited growth of a-Mg grains. The other is the increased dislocation density in the matrix. Heat treatment could enhance both ultimate tensile and yield strengths of the SiCp/AZ91 composite at different testing temperatures. The amplitude of the increase in the strength of was more significant for the SiCp/AZ91 composite subjected to the solution plus aging treatment. Hot-extrusion for the SiCp/AZ91 composite could considerably enhance its ultimate tensile and yield strengths at room and elevated temperatures, and the hot-extruded composite could remain the very high strengths. Compared with the AZ91 matrix alloy, the SiCp/AZ91 composite exhibited the better wear-resistance. In addition, the SiCp/AZ91 composite had lower fracture elongationcompared with the AZ91 matrix alloy. And the testing temperature had no significant effect on the elongation of the SiCp/AZ91 composite. Even at the testing temperature of 200°C, the fracture elongation was a little enhanced for the SiCp/AZ91 composite.At the room temperature, the cleavage plane and tearing ridge, which was usually taken as typical brittle fracture features, could be seen on the tensile fracture surfaces of the SiCp/AZ91 composite. At the elevated temperatures, however, the tensile fracture surface of the SiCp/AZ91 composite was composed of the cleavage plane, tearing ridge and dimple with small size. It implied that the SiCp/AZ91 composite showed a mixed ductile and brittle fracture feature.更多还原