超高强铝合金Al-12Zn-2.4Mg-1.2Cu热变形特性及应用研究

发布时间：2018-05-15 23:03

  本文选题：超高强铝合金 + 变形特性　； 参考：《中北大学》2016年博士论文

【摘要】：超高强铝合金具有高的比强度和硬度、耐久且经济、易于加工、较好的耐腐蚀性能和较高的韧性等优点,已成为航空和航天、兵器、交通运输等行业首选结构材料之一。以自主研发的超高强铝合金(Al-12Zn-2.4Mg-1.2Cu-0.3Zr-0.05 Ni)为研究对象,通过热模拟试验展开合金的热变形特性研究;在开展不同工艺参数对合金力学性能影响的基础上,以某型号用心部双凸盘形零件作为应用目标构件,针对其高服役性能和性能均一性要求,结合合金自身应力敏感性特点,提出了状态参量(?'和?)和过程参量(W??)作为均匀性评价指标,开展成形方案设计及成形均匀性研究;采用灰色关联理论与正交试验法相结合的优化设计方法,借助于数值仿真技术,开展了目标构件均匀成形工艺参数优化设计研究;最后,进行了成形试验和构件性能均一性研究。通过热模拟试验,开展了合金热变形特性研究;通过构建热加工图,获得了不同真应变下的最佳变形工艺参数窗口;在经典Arrhenius模型的基础上,采用应变补偿和应变速率敏感指数修正相结合的方法,构建了综合考虑应变补偿和应变速率指数修正的模型。与经典模型相比,预测精度提高了24.88%。基于流变曲线和加工硬化率理论,开展了合金动态再结晶临界条件研究,构建了合金发生动态再结晶临界应力和应变条件模型。借助于金相检测技术,开展了不同变形条件下的动态再结晶微观组织观察与表征研究,结果表明:合金的再结晶晶粒平均尺寸随温度的升高、应变速率的降低而增大;随温度的降低、应变速率的增加而减小。在此基础上,借助于定量金相分析技术和形态学图像处理技术,建立了合金的微观组织模型,为后续数值仿真研究提供材料模型。通过挤压比试验,开展了不同工艺参数下合金力学性能响应研究,结果表明:变形温度和挤压比对合金力学性能具有较显著的影响。与初始挤压棒材室温力学性能(抗拉强度700-720MPa)相比,经二次变形后的抗拉强度提高了7.9%-15.6%。针对目标构件高服役性能及均一性要求,结合合金自身应力敏感性特点,从微观结构和能量状态角度,提出了状态参量(等效应变面密度均匀因子,?)、(等效应力面密度均匀因子,?')和过程参量(等效耗散功增量面密度均匀因子,?W?)作为成形均匀性评价指标。并依据状态参量,进行了目标构件成形方案设计,制定出多道次等温成形方案。首次采用了灰色关联度与正交试验法相结合的工艺参数优化设计方法,通过连续工序下多个变形参数、应力和应变状态结果以及能量分布状态结果的灰色关联度分析,实现了多评价指标的关联集成,解决了正交试验法无法开展多评价指标下成形工艺参数优化设计难题。在此基础上,获得多道次等温成形工艺参数组合和连续工序下不同因素对成形均匀性影响的显著关系。最后,进行了目标构件的成形试验和微观组织与性能测试表征研究。结果表明:所制定的多道次等温成形(case2)工艺方案合理可行。case2方案成形构件的室温抗拉强度均值大于730MPa,伸长率均值大于5%;较单道次成形(case1)方案分别提高了5.3%和2.3%。case2方案成形构件的力学性能在要求取样的方向上无显著差异(P-value=0.168806),有效保障了成形构件力学性能一致性;且微观组织中再结晶体积分数更高,平均晶粒尺寸更加细小,有效保障了成形构件微观组织的均匀性。case1方案成形构件的抗拉强度在要求取样的方向存在显著差异(P-value=0.780749)。采用case2方案和优化设计后的工艺参数制备出了力学性能一致性较好的构件,为该合金在目标构件均匀成形及工程化应用奠定了基础。
[Abstract]:Ultra high strength aluminum alloy has the advantages of high specific strength and hardness, durable and economical, easy to process, good corrosion resistance and high toughness. It has become one of the preferred structural materials in aviation and aerospace, weapons, transportation and other industries. The research object is Al-12Zn-2.4Mg-1.2Cu-0.3Zr-0.05 Ni, which is developed independently. On the basis of the influence of different technological parameters on the mechanical properties of the alloy, the double convex disc parts of a certain type of heart were used as the target component, and the state parameters (? ') were put forward on the basis of the characteristics of the high service performance and uniformity of the alloy and the stress sensitivity characteristics of the alloy. And?) and process parameters (W?) as the index of uniformity evaluation, the design of forming scheme and the study of forming uniformity are carried out. The optimization design method which combines the grey relation theory with the orthogonal test method and the numerical simulation technology is used to carry out the optimization design of the uniform forming process parameters of the target component. Finally, the forming test and the forming test are carried out. The thermal deformation characteristics of the alloy were studied by the thermal simulation test. Through the construction of the thermal processing diagram, the optimum parameters window of the deformation process under different true strain was obtained. On the basis of the classic Arrhenius model, the combination of strain compensation and strain rate sensitivity index correction was used to construct a comprehensive test. In comparison with the classical model, the prediction accuracy of the model is improved by 24.88%. based on the rheological curve and the theory of machining hardening rate. The critical conditions for dynamic recrystallization of the alloy are studied, and the critical stress and strain condition model of the alloy's dynamic recrystallization is constructed. The microstructure observation and characterization of dynamic recrystallization under different deformation conditions show that the average size of recrystallized grain increases with the increase of temperature and strain rate, and decreases with the increase of temperature and strain rate. On this basis, the quantitative metallographic analysis and morphological image processing are used. The microstructure model of the alloy was established, and the material model was provided for the subsequent numerical simulation. The mechanical properties of the alloy under the different process parameters were studied by the extrusion ratio test. The results showed that the deformation temperature and extrusion ratio had a significant influence on the mechanical properties of the alloy. Compared with the tensile strength 700-720MPa, the tensile strength after two times of deformation increases the high service performance and homogeneity of the target member by 7.9%-15.6%.. According to the characteristics of the stress sensitivity of the alloy, the state parameters (equivalent strain surface density uniformity factor,?) are proposed from the micro structure and energy state. The process parameters (the equivalent of the equivalent dissipative energy increment surface density factor, W?) are used as the evaluation index of the forming uniformity. The forming scheme of the target component is designed according to the state parameters, and the multi-channel isothermal forming scheme is formulated. The method of optimizing the process parameters combining the grey correlation with the orthogonal test method is first adopted. The grey correlation analysis of multiple deformation parameters, stress and strain state results and energy distribution state results in the continuous process has realized the association integration of multi evaluation index, and solved the problem of optimization design for forming process parameters under the multi evaluation index of orthogonal test. On this basis, the multi pass isothermal forming process was obtained. The significant relationship between the parameters combination and the influence of different factors on the forming uniformity in the continuous process. Finally, the forming test of the target component and the characterization of the microstructure and performance test are carried out. The results show that the multi pass isothermal forming (case2) process is reasonable and feasible, and the mean of the tensile strength of the forming component at room temperature is larger than that of the.Case2 scheme. In 730MPa, the average elongation is greater than 5%, and the mechanical properties of the 5.3% and 2.3%.case2 schemes have no significant difference (P-value=0.168806) in the direction of sampling, which can effectively guarantee the mechanical properties of the forming components, and the volume fraction of the recrystallization in the microstructures is higher, and the average grain size is higher. The size is more small and the microstructure uniformity of the forming component is effectively guaranteed. The tensile strength of the.Case1 forming component is significantly different in the direction of the required sampling (P-value=0.780749). The components with good mechanical properties are prepared by using the case2 scheme and the optimized design parameters, which is the alloy in the target component. The foundation of the homogenization and engineering application is laid.

【学位授予单位】：中北大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG146.21
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本文编号：1894325