【作者】 蹇海根；

【导师】 姜锋；

【作者基本信息】 中南大学 ， 材料物理与化学， 2010， 博士

【摘要】 结合高强B93铝合金的国产化研制,利用室温拉伸、金相(OM)、扫描电镜(SEM)、透射电子显微镜(TEM)、差热分析和X射线衍射(XRD)等分析手段,研究了不同状态下高强B93合金性能和组织的变化规律,优化了热处理制度。重点研究了B93合金棒材的疲劳性能及断裂行为,采用背散射电子衍射(EBSD)技术研究合金疲劳裂纹扩展过程的晶体学机制。结合工业化生产条件,采用热模拟技术研究了合金的热加工工艺,采用ANSYS有限元模拟与实验的方法研究了合金淬火工艺,制订的热加工与固溶、时效热处理已用于工厂指导该合金的批量生产。论文研究获得以下主要结论：(1)通过对B93合金棒材进行热模拟研究,建立了该合金高温塑性变形流变应力本构方程,确定了合金加工图中不稳定性流变区域,优化了可加工温度和应变速率,获得的最佳工艺参数能为合金棒材大批量工业化生产提供了支持。(2)对大规格B93合金棒材的淬火温度场进行了有限元模拟,确定棒材的淬透层深度和临界淬火冷却速度,评定了合金棒材的淬火敏感性,建立了大规格B93合金棒材淬火冷却速率-性能-微结构之间关系。(3)对B93合金棒材的大量疲劳试验数据进行统计分析,计算了B93合金棒材的中值S-N曲线和存活率为99.9%的p-S-N曲线方程,全面了解该合金棒材的综合疲劳性能。(4)通过疲劳断口形貌观察及疲劳裂纹扩展的EBSD分析,研究了B93合金棒材疲劳裂纹的萌生、扩展以及断裂机制,并从晶体学角度提出了新的疲劳裂纹扩展晶体学模型。(5)利用ANSYS有限元模拟技术,分析含裂纹的B93合金棒材中的应力分布情况,计算出应力强度因子,结合K判据初步揭示裂纹的运动状态,从而评定B93合金棒材的服役安全可靠性。更多还原

【Abstract】 Based on production researches on high strength B93 aluminum alloy, the properties and evoloution of microstructures of B93 alloy under various conditions were studied by using tensile testing, optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), differential scanning calorimetry (DSC) and X-ray diffraction, and the technology for heat treatment was optimized. Intensive studies were made on the fatigue property and fracture behaviours of B93 alloy bars, and the crystallographic mechanism of fatigue crack propagation were investigated by using electron back-scattered diffraction (EBSD) techniques. Besides, considering industrial production, the hot working process of this kind of alloy was studied by using thermal simulation techniques and the quenching process was investigated by combining ANSYS finite element modelling and experiments. Technics of hot working and solution, aging treatment obtained from these have already been applied to give directions in factory production. The research have come to the conclusion that:(1) The flow stress constitutive equation of alloy during pyroplastic deformation was established by carrying on thermal simulation researches of B93 alloy bars. Hence unstable flow areas in processing map have been determined and processing temperature and strain rate were optimized. The optimal processing parameter provide support for mass commercial production of alloy bars.(2) Finite element modelling of quenching temperature field of large scale B93 alloy bars contributes to determine the depth of quenching layer and critical cooling rate, and evaluate the quench sensitivity of alloy bars. Thereby the relationship among cooling rate, property and microstructure of large scale B93 alloy bars was established.(3) The S-N curve and equation of p-S-N curve (with a survivability of 99.99%) of B93 alloy bars were obtained from statistical analysis of mass fatigue tests data.(4) Mechanisms of fatigue crack initiation, propagation, and fracture were investigated by using fracture morphology observation and EBSD analysis of fatigue crack, and a new crystallographic model of fatigue crack propagation was given.(5) Stress distribution condition of B93 alloy bars with cracks was analyzed by ANSYS finite element modelling techniques and the stress intensity factor was figured out. Combining the stress intensity factor and K criterion, the motion state of crack could be revealed, which helps evaluate safe reliability of B93 alloy bars.更多还原