【作者】 刘佳；

【导师】 龚海； 周逵；

【作者基本信息】 中南大学 ， 机械（专业学位）， 2024， 硕士

【摘要】 2219铝合金作为一种轻质化高强度铝合金,被广泛应用于液体火箭推进器箱以储存液体燃料,铸造作为箱体制造的首道工艺,铸锭的初始状态直接影响后续的工艺进行和构件性能,铸锭的晶粒尺寸作为评价构件质量的指标之一,与材料性能息息相关。因此需要获得晶粒尺寸信息进而调控后续的制造工艺。本文针对破坏性试验检测晶粒尺寸周期长且不能评价工件整体晶粒尺寸的问题,研究超声波在2219铝合金铸锭中的传播特性,并对超声表征铸锭晶粒尺寸的整体检测方式进行探究。分析超声声速、时频域衰减系数、背散射特征值与铸锭平均晶粒尺寸之间的关系,最终建立2219铝合金铸锭晶粒尺寸的超声评价模型,主要研究内容有以下几方面:1、超声波在铸锭多晶体结构中的传播特性研究。利用MATLAB和COMSOL建立了2219铝合金晶体结构的仿真模型,解释了晶体的各向异性是导致声波散射的主要原因。分析了检测频率、晶粒尺寸、晶粒形貌及激励方式对衰减系数、声速的影响。当晶粒尺寸与波长接近时,晶粒尺寸与衰减系数、声速之间存在线性关系,为利用超声特性表征晶粒尺寸提供了理论指导。2、2219铝合金铸锭晶粒尺寸表征的超声特征信号研究。通过金相分析得出,从铸锭外缘至心部,晶粒尺寸逐渐增大的分布规律。建立了不同频率下、不同晶粒尺寸对应的时域衰减特性、声速、频域衰减特性和频域背散射特征值的变化关系式,为铸锭晶粒尺寸分布的超声表征提供了方法指导。3、2219铝合金铸锭晶粒尺寸分布的超声频域表征方法研究。根据铸锭的晶粒尺寸分布规律,针对端面检测采用了频域衰减法表征晶粒尺寸;针对柱面检测,通过分析不同深度对应的背散射信号,提出了一种频域背散射特征差异法以表征不同深度区域的平均晶粒尺寸,评价误差均在20μm之内。图83幅,表27个,参考文献91篇。更多还原

【Abstract】 As a lightweight and high-strength aluminum alloy,2219aluminum alloy is widely used in liquid rocket propellant tanks for storing liquid fuel.Casting is the first process for manufacturing the tank,and the initial state of the ingot directly affects the subsequent process and component performance.Grain size,as an evaluation of the quality of the component as one of the indexes,is closely related to the material properties.Therefore,it is necessary to obtain the grain size information to regulate the subsequent manufacturing process.In this thesis,aiming for issues that the destructive test has failed to evaluate the overall grain size of the workpiece and had a long cycle,ultrasonic propagation characteristics in 2219 aluminum alloy ingots are studied,and the overall detection method is explored for ultrasonic characterization of the ingot grain size.The correlation between the grain size of the ingot and ultrasonic characters is analyzed,including ultrasonic sound velocity,attenuation coefficient in both the time domain and the frequency domain,and backscattering signal eigenvalues.Finally,the ultrasonic evaluation models are established for the grain size of 2219aluminum alloy ingot,the main research content has the following aspects:1.Research on propagation characteristics of ultrasonic wave in the ingot polycrystalline structure.The simulation model of 2219 aluminum alloy crystal structure is established by using MATLAB and COMSOL,which explains that the anisotropy of the crystal is the main reason for the scattering of the acoustic wave.The attenuation coefficient and sound velocity are analyzed concerning the effects of detection frequency,grain size,grain morphology,and excitation direction.When the grain size is close to the wavelength,there is a linear relationship between the grain size and the attenuation coefficient and the speed of sound,which provides a theoretical basis for the use of ultrasonic properties to characterize the grain size.2.Research on 2219 aluminum alloy ingot grain size characterization by ultrasonic characteristic signal.By metallographic analysis,it is concluded that from the outer edge to the center of the ingot,the grain size gradually increases in the distribution law.The relationship equations of time-domain attenuation characteristics,sound velocity,frequency-domain attenuation characteristics,and frequency-domain backscattering signal eigenvalues corresponding to different grain sizes at different frequencies are established,which provide methodological guidance for the ultrasonic characterization of ingot multi-grain size distribution.3.Research on the ultrasonic frequency domain characterization methods for the grain size distribution of 2219 aluminum alloy ingot.According to the grain size distribution law of ingot,the frequency domain attenuation method was adopted to characterize the grain size for axial detection;for radial detection,a method based on the difference of frequency-domain backscattering eigenvalues is proposed to characterize the average grain size in different depth areas by analyzing the backscattering signals corresponding to different depths.Both the evaluation errors by the characterization methods are all less than 20μm.更多还原