高低频协同振动下Al-Si合金熔液去氢机理与振源控制研究

发布时间：2018-06-17 06:12

本文选题：Al-Si合金 + 去氢　；参考：《山东大学》2016年硕士论文

【摘要】：Al-Si合金材料因其质量轻、强度高和导热性、流动性好等优点,广泛的应用于诸多领域。根据分析,铝合金中溶解的气体有85%为氢气,熔体的“含气量”可近似等同于“含氢量”。由于液态Al-Si合金的氢溶解度较高,当熔体冷却至固态时,氢溶解度将大大降低,从而过饱和的氢将释放,在铸件内部形成分散性的细小气孔,致使铸件的力学性能、抗疲劳性能、耐腐蚀性、延展性均大大降低。因此,除气(去氢)是增强Al-Si合金的综合机械性能的主要措施。本文为优化精炼品质,提高氢净化率,主要内容如下：(1)分析了Al-Si合金熔体中氢的动力行为。通过在滨州活塞公司进行的BH122A牌号的Al-Si合金精炼后回氢规律测定实验,验证了氩气搅拌除气后的回氢规律。为减少熔体回氢,进一步提高氢净化率,确定了基于超声振动的二次除气方法；(2)通过对Al-Si合金熔液中声场规律的研究,确定了工具杆下方的声压场分布场；通过对空化阈值特性的研究,确定了有效空化作用范围,此外,通过对瞬态空化与稳态空化规律的研究,确定了在熔体去氢过程中稳态空化将起到重要作用,为气泡上浮模型的建立提供了必要条件；(3)气泡的生长与上浮规律,是影响Al-Si合金熔体除气效果的关键因素。基于Rayleigh-Plesset二阶微分方程对气泡生长规律进行了研究。考虑由于超声除气的过程中气泡将不断上浮,本文基于Rayleigh-Plesset方程与Stocks模型,建立了气泡上浮全程气泡壁运动的模型；(4)利用Matlab对气泡上浮全程气泡壁运动的模型进行了仿真研究：以气泡的半径变化倍数、上升时间及振荡剧烈程度(以气泡半径最大值与最小值的差值来描述)等为考核数据,通过不同高低频施振频率与施振时间下与超声独立施振作用下仿真结果的对比研究结果表明：协同振动下气泡上浮时间可缩短28.8%,振荡更为剧烈,从机理上证明了提高去氢效果的有效性；(5)本文以压电陶瓷超声换能器为高频振源,超磁致伸缩换能器为低频振源,为使GMA振动系统在10-50Hz内可控,产生稳定的正弦波形。本文基于经典P-I模型,结合相角补偿模型,建立了动态复合前馈补偿系统,相角补偿结合改进型P-I模型的控制方法提高了P-I模型的适用频域,迟滞补偿实验表明该控制方法可有效减小迟滞系统的非线性误差,但在高频情况下,模型精度会受到一定影响。实验结果表明,最大误差容易产生在滞环的拐点附近,即信号的极值点附近。为Al-Si合金超声与低频结合振动除气,提供了可行的控制方案与理论基础。本文主要创新点如下：(1)补充以前研究的局限。基于Rayleigh-Plesset方程与Stocks模型,建立了气泡上浮全程的运动的模型；(2)利用Matlab进行了仿真研究,通过高低频结合施振与超声独立施振作用下气泡的半径变化倍数,上升时间,振荡剧烈程度的对比,确定更有利于气泡的上浮和振荡的高低频振动优化参数组合(功率、频率、作用时间)；(3)基于经典P-I模型,结合相角补偿模型,建立了GMA动态复合前馈补偿系统,相角补偿结合改进型P-I模型的控制方法提高了P-I模型的适用频域,有效改善了低频振动的波形。研究结果的意义：(1)本文研究了Al-Si合金的去氢机理,提出的声场作用下的气泡上浮模型能直观体现声波对气泡的激励作用,对于了解声波除气的机理和本质有一定的理论意义。(2)本文提出的GMA控制方法,能显著改善振源波形,为搭建高低频复合振动,提供了有效的控制方法,具有一定的应用意义。
[Abstract]:Al-Si alloy material is widely used in many fields because of its light quality, high strength, good thermal conductivity and good fluidity. According to analysis, 85% of the dissolved gas in aluminum alloy is hydrogen, and the "gas content" of the melt can be approximately equal to "hydrogen content". Because of the high hydrogen solubility of liquid Al-Si alloy, when the melt is cooled to solid, hydrogen is used. The solubility will be greatly reduced, thus the supersaturated hydrogen will be released and the dispersed small pores are formed inside the castings, which greatly reduce the mechanical properties, fatigue resistance, corrosion resistance and ductility of the castings. Therefore, degassing (dehydrogenation) is the main measure to enhance the comprehensive mechanical properties of Al-Si alloys. This paper is to optimize the refining quality and improve the hydrogen. The main contents are as follows: (1) the dynamic behavior of hydrogen in Al-Si alloy melts was analyzed. The law of hydrogen recovery after argon stirring was verified by the test of the recovery of hydrogen after refining the BH122A grade of Al-Si alloy in the Piston Corp of Binzhou. The two degassing method is moved; (2) the distribution field of sound pressure field under the tool bar is determined by the study of the sound field law in the molten liquid of Al-Si alloy. The effective cavitation range is determined by the study of the characteristics of the cavitation threshold. In addition, through the study of the law of transient cavitation and steady cavitation, the steady state in the process of dehydrogenation of the melt is determined. Cavitation will play an important role and provide necessary conditions for the establishment of bubble floating model. (3) the growth and floating law of bubbles are the key factors affecting the degassing effect of Al-Si alloy melt. Based on the two order differential equation of the bubble, the bubble growth law is studied. On the basis of the Rayleigh-Plesset equation and the Stocks model, the model of bubble wall motion is established in this paper. (4) a simulation study of the bubble wall motion model by using Matlab is carried out by using the radius of the bubble radius, the rise time and the intensity of vibration (the maximum and the minimum of the bubble radius). Compared with the simulation results under the action of different high frequency vibration frequency and vibration time and ultrasonic independent vibration, the results show that the floating time of bubbles can be shortened by 28.8% and the oscillation is more intense under the cooperative vibration. The effectiveness of improving the dehydrogenation effect is proved in mechanism. (5) this paper is based on the piezoelectricity. The ceramic ultrasonic transducer is a high frequency oscillator, and the super magnetostrictive transducer is a low frequency oscillator. In order to make the GMA vibration system controllable in the 10-50Hz and produce a stable sinusoidal waveform. Based on the classic P-I model and the phase angle compensation model, a dynamic compound feedforward compensation system is established. The phase angle compensation and the improved P-I model are improved. The P-I model is applied to the frequency domain and the hysteresis compensation experiment shows that the control method can effectively reduce the nonlinear error of the hysteresis system, but the model accuracy will be affected by the high frequency. The experimental results show that the maximum error is easily produced near the turning point of the hysteresis loop, that is, near the extreme point of the signal. It is the combination of the ultrasonic and low frequency of the Al-Si alloy. Vibration degassing provides a feasible control scheme and theoretical basis. The main innovation points of this paper are as follows: (1) supplement the limitations of previous studies. Based on the Rayleigh-Plesset equation and Stocks model, a model of the movement of the whole process of bubble floating is established. (2) the simulation study is carried out by using Matlab, and the combined vibration and ultrasonic vibration of the high and low frequencies are used for the independent vibration of vibration. On the basis of the classical P-I model and the phase angle compensation model, a GMA dynamic compound feedforward compensation system is established based on the classical P-I model and the phase angle compensation mode, and the phase angle compensation combination is combined. The control method of the improved P-I model improves the applicable frequency domain of the P-I model and effectively improves the waveform of the low frequency vibration. The significance of the research results is as follows: (1) the dehydrogenation mechanism of Al-Si alloy is studied in this paper. The bubble floating model under the action of sound field can directly reflect the excitation effect of sound waves on the bubble and the mechanism of understanding the acoustic degassing of sound waves. And the essence has some theoretical significance. (2) the GMA control method proposed in this paper can significantly improve the waveform of the vibration source. It provides an effective control method for building high frequency complex vibration. It has some practical significance.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG292

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