7055铝合金厚板淬火—预拉伸残余应力演变及预测研究

发布时间：2018-07-01 15:35

本文选题：7055铝合金厚板 + 有限元模拟　；参考：《北京有色金属研究总院》2017年博士论文

【摘要】：7xxx系铝合金具有高强、高韧及综合性能优异等特点,被广泛应用于航空航天领域。随着大规格整体结构件的发展与应用,高性能7xxx系铝合金厚板的需求日益迫切。铝合金厚板残余应力的控制是该领域的研究难点之一。本文以航空用超高强7055铝合金大规格厚板为研究对象,结合有限元模拟和实验测试,系统研究了残余应力分布与演变规律及其影响因素,研究了厚板残余应力表征方法,建立了厚板淬火残余应力分布预测综合方法,探索了不均匀淬火对残余应力的影响规律,为工厂大规格7055铝合金厚板淬火-预拉伸过程中残余应力控制提供可靠的参考。利用ANSYS有限元软件建立了 7055铝合金厚板淬火-预拉伸残余应力有限元模型。通过实验测试确定了 7055铝合金厚板的热物性参数,利用实验和反算法获得了淬火过程中的换热边界条件。研究了淬火残余应力分布及演变规律,淬火残余应力为"外压内拉"分布,拉压转换点位于四分之一厚度位置,厚板内为平面均匀应力状态,仅在厚度方向存在应力梯度。研究了预拉伸对残余应力分布的影响规律,应力消减率随着预拉伸量的增大呈先迅速增大后缓慢增大的趋势。7055铝合金厚板残余应力实验测试与数值模拟综合研究表明:对不同宽度厚板表面应力的测试结果显示出,采用钻孔法与X射线衍射法均具有较好的稳定性和准确性;X射线衍射法表面应力测试结果与有限元模拟结果吻合较好,中子衍射法内应力测试结果与有限元模拟结果基本吻合,验证了有限元模型的准确性;对不同淬火介质参数的厚板进行残余应力表征,采用钻孔法和裂纹柔度法测得的表面应力水平吻合较好,裂纹柔度法内应力测试结果与有限元模拟基本吻合,验证了裂纹柔度法测试的准确性。由此,提出了表面应力测试方法优选原则,建立了基于钻孔法、X射线衍射法和裂纹柔度法的7055铝合金厚板小规格试样残余应力综合表征方法。研究了淬火介质参数对换热系数的影响规律:随着水温或PAG浓度的升高,换热系数水平逐渐降低;随着喷淋水流量的升高,换热系数水平逐渐升高;各淬火介质的换热能力顺序为1 0%NaCl+KNO3溶液20℃水13.76L/min喷淋15%PAG溶液。研究了淬火介质参数对7055铝合金厚板淬火残余应力的影响规律:随着水温的升高,淬火残余应力逐渐降低;随着PAG浓度的升高,淬火残余应力逐渐降低;在各淬火介质参数下7055铝合金厚板淬火残余应力水平为10%NaCl+KNO3溶液20℃水5%PAG溶液。系统研究了尺寸因素对7055铝合金厚板淬火残余应力的影响规律。尺寸因素对应力水平的影响规律为:当长度和宽度较小时应力水平存在峰值,当长厚比和宽厚比均6时,应力水平趋于稳定。尺寸因素对应力分布的影响规律为:应力水平随着长度的增大基本不变,但波动区域比例逐渐减小;随着宽度的增大,应力水平与波动区域比例均逐渐减小;随着厚度的增大,应力水平与波动区域比例均逐渐增大。提出了长向和宽向残余应力分布预测方法,通过该方法和5×5×1模型的长向和宽向淬火残余应力分布,可预测x×y×1模型的长向和宽向淬火残余应力分布,其中x≥y≥5。通过对不同宽度7055铝合金厚板表面淬火残余应力的测试与模拟研究,验证了长向和宽向应力分布预测方法是可行的。通过研究不同厚度和不同淬火介质参数厚板的厚向应力分布函数和心部应力水平预测模型,建立了厚向淬火残余应力分布预测模型。结合长向和宽向应力分布预测方法以及厚向应力分布预测模型,建立了 7055铝合金厚板淬火残余应力分布预测综合方法,利用小规格试样淬火残余应力分布和大规格厚板表面中心点应力水平可预测大规格7055铝合金厚板淬火残余应力分布。研究了不均匀淬火对7055铝合金厚板残余应力分布的影响规律:当厚板上下表面不对称淬火时,厚向应力分布介于上、下表面平均换热系数对应应力分布之间,中心两侧不对称,应力水平相当于上表面与下表面平均换热系数对应应力水平的平均值;同一表面不均匀淬火时,表面应力分布与不均匀换热系数分布类似,应力水平相当于平均换热系数对应的应力水平,而心部应力分布近似为均匀应力分布状态,应力水平相当于线性分布两极值的心部应力水平的平均值。大规格7055铝合金厚板表面淬火残余应力实测结果的分布线型与多段线性不均匀淬火残余应力分布线型相似。同时研究了预拉伸对不均匀淬火残余应力分布的影响规律,预拉伸对不均匀淬火的心部应力不均匀性具有调控作用,但对表面应力不均匀性无调控作用。
[Abstract]:7xxx aluminum alloy has been widely used in aerospace field because of its high strength, high toughness and excellent comprehensive performance. With the development and application of large size integral parts, the demand for high performance 7xxx system aluminum alloy thick plate is increasingly urgent. The control of residual stress of aluminum alloy thick plate is one of the difficult problems in this field. The large thickness plate of strong 7055 aluminum alloy is studied. Combined with the finite element simulation and experimental test, the residual stress distribution and evolution law and its influencing factors are systematically studied. The residual stress characterization method of the thick plate is studied. The comprehensive method for predicting the residual stress distribution of the thick plate quenching is established, and the influence of the uneven quenching on the residual stress is explored. A reliable reference is provided for the residual stress control in the process of quenching and predrawing of large size 7055 aluminum alloy thick plate of the factory. The finite element model of quenching and prestretching residual stress of 7055 aluminum alloy thick plate is established by ANSYS finite element software. The thermal physical parameters of the 7055 aluminum alloy thick plate are determined by experimental test, and the experiment and inverse algorithm are used. The heat transfer boundary conditions in the quenching process are obtained. The distribution and evolution of the residual stress of quenching are studied. The residual stress of quenching is "external pressure internal pull" distribution, the transition point of tension and pressure is located in the 1/4 thickness position, the thick plate is a plane uniform stress state, and the stress gradient only exists in the direction of thickness. The distribution of residual stress in pretension is studied. The stress reduction rate increases rapidly and then increases slowly with the increase of pretension, the experimental test and numerical simulation of the residual stress of.7055 aluminum alloy thick plate show that the test results of the stress on the surface of thick plates with different width show that both the drilling method and the X ray diffraction method have good stability and good stability. The results of the surface stress test of X ray diffraction method are in good agreement with the finite element simulation results. The results of the stress test in the neutron diffraction method agree with the finite element simulation results basically. The accuracy of the finite element model is verified. The residual stress of the thick plate with different quenching medium parameters is characterized by the drilling method and the crack flexibility method. The surface stress level is in good agreement. The test results of the internal stress of the crack flexibility method are basically consistent with the finite element simulation, and the accuracy of the test of the crack flexibility method is verified. Therefore, the optimization principle of the surface stress testing method is put forward, and the remnants of the small size sample of 7055 aluminum alloy thick plate based on the drilling method, the X ray diffraction method and the split pattern flexibility method are established. The influence of the quenching medium parameters on the heat transfer coefficient is studied. With the increase of water temperature or PAG concentration, the heat transfer coefficient level gradually decreases. With the increase of the flow rate of spray water, the heat transfer coefficient level increases gradually; the heat transfer capacity of each quenching medium is 1 0%NaCl+KNO3 solution at 20 C 13.76L/min spray 15%PAG The influence of quenching medium parameters on the residual stress of 7055 aluminum alloy thick plate quenching is studied. With the increase of water temperature, the residual stress of quenching gradually decreases. With the increase of PAG concentration, the residual stress of quenching gradually decreases, and the residual stress level of 7055 aluminum alloy thick plate quenched under the parameters of each quenching medium is 10%NaCl+KNO3 solution 20 C 5 water. The influence law of size factors on the residual stress of 7055 aluminum alloy thick plate quenching is studied systematically. The influence law of dimension factors on the stress level is that when the stress level of length and width is at the peak value, when the length to thickness ratio and the width to thickness ratio are 6, the stress level tends to be stable. The influence law of size factors on the stress distribution is that: the stress distribution is the following: the effect of the size factor on the force distribution is: the stress distribution is the following: the effect of the size factor on the force distribution is: the stress distribution is the following: the effect of the size factor on the force distribution is: the stress distribution is the following: the effect of the size factor on the force distribution is: the stress distribution is the following: the effect of the size factor on the force distribution is: the stress distribution is the following: the effect of the size factor on the force distribution is: the stress distribution is the following: the effect of the size factor on the force distribution is: the stress distribution is the following With the increase of the width, the ratio of stress level and fluctuating region gradually decreases with the increase of the width. With the increase of thickness, the ratio of stress level and fluctuation region gradually increases. The prediction method of long direction and wide residual stress distribution is put forward, through this method and 5 x 5 x 1. The distribution of the residual stress in the long direction and wide direction quenching of the model can be used to predict the residual stress distribution in the long direction and wide direction quenching of the x x y x 1 model. In the test and Simulation of the surface quenching residual stress of the 7055 aluminum alloy thick plate with different width, the prediction method of the long direction and wide stress distribution is proved to be feasible by the study of the difference between the long direction and the wide direction quenching of the model. The method of the prediction of the long and wide stress distribution is proved to be feasible. The thick direction stress distribution function of thick plate with different quenching medium parameters and the prediction model of the stress level of the heart are established. The prediction model of the residual stress distribution in the thick quenching is set up. The prediction of the residual stress distribution of the 7055 aluminum alloy thick plate quenching is established by combining the prediction method of the long and wide stress distribution and the prediction model of the thick stress distribution. The residual stress distribution of the large size 7055 aluminum alloy thick plate can be predicted by the residual stress distribution and the center point stress level of the large size plate surface. The influence of the uneven quenching on the residual stress distribution of the 7055 aluminum alloy thick plate is studied. The distribution of the thick stress distribution when the upper and lower surface of the thick plate is quenched asymmetrically. On the upper surface, the average heat transfer coefficient of the lower surface corresponds to the stress distribution, and the stress level is equal to the average stress level corresponding to the average heat transfer coefficient between the upper and the lower surfaces. The surface stress distribution is similar to that of the non uniform heat transfer system when the same surface is unevenly quenched, and the stress level is equivalent to the average heat transfer system. The stress level of the center is approximately equal to the uniform stress distribution, and the stress level is equal to the average of the two extremes of the linear distribution. The distribution line of the measured results of the surface quenching residual stress of the large size 7055 aluminum alloy thick plate is similar to that of the multi segment linear unevenly quenched residual stress distribution line. The effect of pretension on the distribution of residual stress in non uniform quenching is studied. The pretension has a control effect on the stress inhomogeneity of the unevenly quenched heart, but it has no control effect on the surface stress inhomogeneity.
【学位授予单位】：北京有色金属研究总院
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG146.21;TG166.3

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