| Magnesium alloy has a lot of advantages, such as low density, high specific stiffness, specific modulus and good electromagnetic shielding. Widespread application of magnesium alloy in automotive and other industries is good for lightweight design. Moreover, fuel oil consumption will be reduced; as a result, the carbon emissions will be reduced as well. It will also be of great benefit for establishing friendly environment. Our country has the largest reserves, production and exportation of magnesium alloys. Based on the support of National Technology R&D Program in the12th Five-year Plan of China and the Canada-China-USA Collaborative Research&Development Project, the research on NVH characteristics of magnesium alloy was conducted systematically in this paper.Experiments on the damping characteristics of AZ31B magnesium alloy and AZ31B magnesium alloy with anti-corrosion process were conducted by impulse response decay method and their damping loss factors were obtained and compared. The experimental results indicate that the epoxy resin coating produced by the electrophoretic deposition process is the reason for the enhancement of the damping loss factor of the samples with anti-corrosion process. Transverse rigidities of AZ31magnesium alloy and AZ31B magnesium alloy with different thickness were investigated by three-point supporting method, and their Young’s moduli were also obtained. The stifness-to-density ratios of AZ31magnesium alloy and AZ31B magnesium alloy were studied and compared with that of aluminum and steel samples, which have the same surface density. The results indicate that the stiffness-to-density ratio of magnesium alloy is93.2%of that of the steel sample, and is20.6%higher than that of aluminum sample. The transverse rigidities of the friction stir welded AZ31B magnesium alloy joints under various welding parameters were obtained by the three-point method.The sound insulation characteristics of AZ31magnesium alloy with different structures, including2mm-thick and4mm-thick single layer AZ31magnesium alloy plate, single layer AZ31magnesium alloy plate with porous material covered, single layer AZ31magnesium alloy plate with small holes and double layer AZ31magnesium alloy plate. In addition, the effect of different anti-corrosion processes and friction stir welding on the sound transmission of AZ31B magnesium alloy were studied as well. The experimental results indicate that transvers rigidities of AZ31B magnesium alloy were enhanced and reduced by the anti-corrosion process and the friction stir welding, respetively. Moreover, the anti-corrosion process improved the damping performance of AZ31B magnesium alloy. Therefore, the sound transmission loss of samples with anti-corrosion was improved, while reduced by the friction stir welding. Error is introduced in the Discrete Calculation Method proposed by Hashimoto for sound radiation research, and this was proved by introducing a new method for the calculation of the radiation impedance.The combination of the new method for sound radiation impedance calculation and the discrete calculation method was used to study the acoustic radiation properties of AZ31magnesium. The sound radiation power and radiation efficiency of magnesium alloy were obtained and compared with that of the steel and aluminum alloy specimens, which have the same surface density as that of the magnesium alloy samples.Based on the combination of gradient optimization theory and finite element method, composite magnesium alloy plates, including the AZ31magnesium alloy with porous materials covered, the AZ31magnesium alloy with both pore material layer and foam layer covered, were optimized. For the double layer composite magnesium alloy structure, the noise reduction of the optimized model is4.89dB higher than that of the original model. And the porous materials lost weight by3.8%, from4.59g reduced to4.42g. As for the three layer composite magnesium alloy structure, the maximum noise reduction of the optimized model is4.57dB higher than that of the original one. And the total weight of pore material and foam material decreased from7.653g to7.626g,a cut of0.35%.Structure optimization design was carried on AZ31magnesium alloy dash panel by the combination of topology optimization and shape optimization. Then the acoustic and vibration characteristics of both the original and the optimized magnesium alloy dash panels were studied by finite element method and boundary element method, and the comparative study was also carried out. The comparative study results show that the transmission sound power level of the optimized model (Optl and Opt2) is24.8dB lower than that of the original. Opt2model lose weight by4.24%. Optimization design not only improves the sound performance of magnesium alloy dash panel, but also reduces the weight of the structure, and makes the lightweight design come true. The random vibration analysises were conducted on the magnesium alloy dash panels before and after optimization by large mass method. The vibration responses of magnesium alloy dash panels were exported and set as boundary condition for the sound radiation research by boundary element method, and the results indicate that the sound radiation power of the optimized model are significantly lower than that of the original model. The sound radiation power level of Optl and Opt2are lower35.25dB and35.78dB, respectively, than that of the original model. Obviously, optimization of the magnesium alloy dash panel is efficient for the sound radiation reduction under random vibration. |
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